Abstract: This master’s thesis first describes the operating principle of the Z-source inverter and presents several examples of converter topologies with an input impedance network for better comparison with the SSI. Then the operating principle and topology of SSI are described, as well as the utilized PWM methods. Equations for the calculation of inductor current and capacitor voltage ripples of the SSI, known from the literature, are given. For the given input parameters, the required inductance and capacitance values are calculated considering the utilized PWM methods. Attention is drawn to the influence of the magnetic saturation of the inductor on its inductance when the respective current increases, and the corresponding effective inductance curve was experimentally determined as a function of the inductor’s current. A model of an ideal three-phase SSI was built in the MATLAB-Simulink environment so as to obtain simulations results for the four considered PWM methods. Then a laboratory prototype of the three-phase SSI-based system was realized and experimental tests were carried, again with the four considered PWM methods. Also, additional experimental tests were carried with the MSVPWM method, which previously proved to be the best, and the obtained results were compared with the expected results, i.e., those based on theoretical considerations and previously performed simulations. As part of the experimental tests, the operating temperature of the system components was additionally determined using a thermal imaging camera in order to determine whether there are any deviations from the permitted values in this regard.

Abstract: U ovoj doktorskoj disertaciji predstavljen je napredni regulacijski sustav prekidačkog reluktantnog generatora s asimetričnim mosnim pretvaračem čiji je cilj minimizacija gubitaka generatora. Izrađen je napredni model prekidačkog reluktantnog generatora koji uključuje međuinduktivne veze između susjednih namota generatora, gubitke u željezu te remanentni magnetski tok. Svi potrebni ulazni podaci za izradu ovog modela dobiveni su eksperimentalno na laboratorijskoj maketi regulacijskog sustava s prekidačkim reluktantnim generatorom. Rezultati dobiveni korištenjem naprednog simulacijskog modela regulacijskog sustava s prekidačkim reluktantnim generatorom, utemeljenom na naprednom matematičkom modelu ovog stroja koji uključuje međuinduktivitete, remanenciju i gubitke u željezu, najprije su uspoređeni s rezultatima dobivenim korištenjem klasičnog simulacijskog modela, u kojem su zanemareni spomenuti efekti, a potom i s eksperimentalnim rezultatima. Ustanovljeno je da se rezultati dobiveni naprednim modelom regulacijskog sustava bolje slažu s eksperimentalnim rezultatima. Naprednim modelom prekidačkog reluktantnog generatora utvrđena je izražena korelacija između srednje vrijednosti svih faznih struja i gubitaka u stroju. Ova korelacija potvrđena je i eksperimentalno. Budući da se srednja vrijednost svih faznih struja može jednostavno odrediti eksperimentalno, razvijen je algoritam pomaka i promatranja koji se temelji upravo na toj varijabli. Osnovna svrha ovog algoritma je pronaći optimalan položaj rotora pri kojem se uklapaju tranzistori u granama asimetričnog mosnog pretvarača da bi se postigli minimalni gubici u stroju. Algoritam koristi iznose i promjene srednjih vrijednosti svih faznih struja i promjenu položaja rotora pri kojem se uklapaju tranzistori iz prethodne iteracije da bi odredio iznos i smjer u kojem će se navedeni položaj promijeniti u sljedećoj iteraciji.

Abstract: The thesis describes the specificity of the axial electric motor with permanent magnets and compares it with a competitive radial electric motor. The main motor parameters that are key to the application of electric motor optimization are described and a table of slot and pole ratios is provided. Proper selection of the slot and pole ratio enables a high winding factor and a balanced system. The main characteristics of magnets are also described along with the method of their application within magnetic circuits in order to enable proper utilization of the magnetic mass. The application of SMC as a component of the stator of an axial electric motor is described and its advantages in application and manufacture are listed. Then, the basic equations of the electric motor are given, which show the dependence of power and torque on electrical quantities. Finally, the design of an axial electric motor with permanent magnets was carried out in the Solidworks software package and its EMS add-on. The YASA topology was chosen, which offers the advantages of shorter magnetic paths and lower losses. The selected slot-pole ratio offers a high winding factor and allows the use of optimal stator core dimensions for the selected magnetic flux. This ratio also allows the use of simple coils with smaller end windings without unnecessary accumulation of copper at too great a distance from the core. The selected magnets offer a large amount of flux with a third harmonic in the gap that will not be reflected in the gap due to the use of a star. The thickness of the plates is determined based on the ratio of the inner and outer radius and the magnetic induction in the gap in order to avoid excessive bending of the plates. By conducting simulations, it was determined that the axial electric motor offers very high values ​​of power density and efficiency with satisfactory field weakening.

Abstract: As the electricity demand constantly grows, the world is increasingly focusing on generating electrical energy from renewable sources, especially from wind and sun (fluctuating characteristic), whose share is continuously increasing. Additionally, market liberalization and various global crises can cause electricity prices fluctuations. One of the solutions to achieve a more secure and reliable power system due to the presence of a high share of fluctuating energy and the improvement due to electricity price volatility, is the energy storage use. In addition, it is necessary to develop efficient methods for optimizing the energy storage operation in order to achieve the desired goal. In this doctoral dissertation, a optimization model for energy storage operation in a market-oriented power system, is developed. The model does not focus on the specifics of individual technology, but optimizes the storage operation primarily for the daily charging and discharging cycle. The model was developed using the optimization technique of mixed-integer linear programming. The development of the general model aims to enable the user can make various simulations and optimizations of the energy storage in a market conditions, such as the optimization of the storage system only, the energy storage with some additional production sources and the overall system with all production sources. The model takes into account the operation of other commonly used production plants by modeling the operation of a single representative production plant that approximates of all other plants of the same type. The applicability of the developed model is presented through four groups of calculations. In the first group of calculations, the influence of one storage parameter on the storage optimal operating mode, was investigated. In the second group, it was shown what influence the energy storage has on the reduction of costs, due to the undelivered energy of production companies. The third group have analysed the impact of energy storage size on the operation of the overall system. The fourth group of the calculations have investigated the influence of the power system structure on the energy storage operation, specifically the increase in the share of storage hydropower plants production and the share of intermittent renewable energy production.

Abstract: In the introductory part of the paper, the reasons for voltage regulation in the distribution network are explained, which is necessary for the purpose of ensuring, on average, equal amounts of voltage for network users as close as possible to the nominal value. Then the entire electric power system is described, what it consists of and how it is divided, all the way to the end users, i.e. consumers. In the third chapter, the need for voltage regulation is described more precisely and some general methods of voltage regulation of the distribution network are given. After presenting the general methods of voltage regulation, the fourth chapter explains in more detail the methods of passive and active regulation, such as automatic regulation of the HV or MV bus of the main substation, voltage compensation, voltage regulation using active sources in the network, optimization algorithm. In the last part of the work, the optimization of the voltage conditions and the position of the transformer switches was carried out using mathematical programming. The optimization was performed on a modified IEEE 33-bus model extended with distributed sources. After the analyzes carried out, we can notice an improvement in voltage conditions along the entire network.

Abstract: The paper presents a tool for calculating the profitability of investment in small photovoltaic power plants. At the beginning of the paper, the basic goals of European countries regarding consumption from renewable energy sources are presented. Then the basic parts of the photovoltaic system (photovoltaic cell, photovoltaic module, inverter and meter) are described and the methods of connecting solar power plants to the power grid are described too. This is followed by a section in which incentives and laws are presented for the purpose of encouraging ever-increasing production from renewable energy sources, including solar energy. Then, the procedure for calculating solar radiation (Liu-Jordan, Klein method) is described, which is later used in the cost-effectiveness calculation tool. The last chapter presents the basic economic parameters used in solar power plant profitability analyzes (discounting, internal rate of return method, present value method, future value method,…). Also a tool (excel document) for calculating the profitability of investments in solar power plants are presented, which was applied at several locations in Croatia. The calculation results are tabulated and commented on for each location.

Abstract: Electricity generation through distributed sources is increasingly used in the power system. Some benefits of this method of production are: production of electricity with less environmental pollution, lower price of electricity (thus higher economic profitability), higher quality of delivered electricity, potentially reduced investment in the electricity system. In this paper, we examine the pros and cons of integrating a distributed energy source into the electricity grid. In the second chapter, we talked about renewable electricity producers. In the third chapter, we dealt with the impact of renewable energy sources on the power system as well as the impacts on short circuits and losses in the network. The fourth chapter deals with the connection of the distributed system to the electricity network. An overview of the conditions and rules for connection and optimization of the connected distributed source is given. In the fifth chapter we talk about the challenges and solutions in production through distributed sources. Also, the principle of parallel and island operation of the source and the prevention of the negative effect of the distributed source on the electricity system are explained. In the sixth chapter, we made an analysis of a part of the power system to whose busbars we connected two wind power plants and two photovoltaic power plants. We have processed two cases: when the listed distributed sources are switched off, and when they work with their maximum power, and we have shown the impact of these sources on voltage conditions and labor losses in the network

Abstract: THE IMAPCT OF ELECTRIC VEHICLE CHARGING STATION CONNECTION ON THE ELECTRICAL NETWORK AND THE POSSIBILITY OF IMPROVING NETWORK CONDITIONS THROUGH OPTIMAL CHARGING

Abstract: In this paper, the SOC of two lead-acid batteries of different ages and capacities of 75 Ah was estimated at the simulation level. The SOC was estimated using the open-circuit voltage method and the Coulomb counter method. Battery models based on an equivalent circuit were used in the simulations, namely the standard GNL model and a new, modified GNL battery model. The paper first describes different battery models and methods for estimating SOC that can be found in the literature. Then, based on experimental measurements, the parameters of resistors and capacitors in the models used were determined, as well as the characteristics of the dependence of SOC on the open-circuit voltage. The model used for the simulations was implemented in the MATLAB-Simulink software package. All components used, their roles and the corresponding parameter values ​​were listed and described. Then, the voltage responses of the battery models used were simulated, which were compared with the experimentally recorded responses, and the SOC responses. The results of SOC estimation using the Coulomb counter method were considered as reference and compared with the results of SOC estimation using the open circuit voltage method. The need for creating a modified GNL model with its associated components was explained, and the values ​​of the integral of the absolute error of voltage and SOC obtained with the considered models were determined and compared, as well as the percentage error of the SOC value obtained based on these models. Finally, a discrete SOC estimator was created, which can be experimentally implemented for real-time SOC estimation.

Abstract: This doctoral dissertation presents three new control systems with a quasi-Z-type inverter powered by a photovoltaic source. The first system is battery-free and the inverter operates in grid connection, while the other two systems are battery-operated and the inverter operates in one case in grid connection and in the other in island mode. A new pulse-width modulation was used to control the quasi-Z-type inverter, with an added third harmonic and an implemented dead time, in which the start of the firing state is synchronized with the start of the zero state and which results in a significant reduction in semiconductor losses. Two new algorithms for calculating semiconductor losses of a quasi-Z-type inverter controlled by the new pulse-width modulation were developed, the accuracy of which was experimentally verified. The first new control system with a quasi-Z-type inverter powered by a photovoltaic source and connected to the electrical grid ensures tracking of the maximum power point without oscillations and without measuring the current of the photovoltaic source. The simulation analysis of this system was performed for a new dynamic model of a photovoltaic source with two diodes and taking into account the effect of the depletion region capacity and the diffusion capacity of each diode. The second new regulation system with batteries assisted by a quasi-Z-type inverter in island mode uses the battery current instead of the source current to search for the maximum power point of the photovoltaic source, while the third new regulation system with batteries assisted by a quasi-Z-type inverter, in grid mode, uses the d-component of the grid current vector for the same purpose. Experimentally confirmed transfer functions obtained based on a new linearized average mathematical model of the system were used to synthesize both battery-based regulation systems.

Abstract: In the first, introductory chapter, the transformer was mentioned as the main element of this thesis. The aim of the thesis and the division into chapters are explained too. The second chapter is theoretical and contains a description of the transformer and its characteristics, including its nominal values. In the continuation of the second chapter, as part of the short-circuit and no-load operating states, the experiments during these operating states, which were preformed in the next chapter, are explained. The third chapter is the practical part of the thesis, in which a total of 4 measurements were made in 2 operating states of the transformer: short-circuit and no-load state of the transformer in positive and zero sequence. From those 4 measurements, 4 tables with results were obtained, which in the fourth chapter will be used for modeling that three-phase two-winding transformer in the EMTP – RV software package. The entire modeling process in the software package EMTP – RV of the three-phase two-winding transformer on which the measurements were preformed is described in the fourth chapter. In each of the subchapters, it is explained how the user windows should be filled within the elements of the scheme representing the basic characteristics of the transformer, the transverse branch and the saturation of the transformer. The final, fifth chapter contains the conclusion of the thesis.

Abstract: In this thesis, MPPT methods for a PV system with a buck converter, a programmable load and batteries are analyzed at the experimental level. The analysis considers two direct MPPT methods (P&O and IC) and two indirect MPPT methods (constant voltage method and fixed power factor method). First, the basic features and types of PV modules are described, as well as the influence of changes in insolation and temperature on the power characteristics of PV modules. Furthermore, the buck converter and the operating mode used in the analysis are described, and then the MPPT methods and their algorithms are discussed. Then, all elements and parameters used to realize the laboratory model are described in detail. A programmable DC source was used as a PV module emulator, while a programmable AC/DC load was used to simulate the load, to which lead-acid batteries were connected in parallel. The model of the control algorithm was created in MATLAB Simulink, with the use of appropriate blocks from the dSpace library for the acquisition of measured signals and the generation of control PWM pulses, which enable the execution of the algorithm in real time using the DS1104 card. At the very end, recorded dynamic experimental responses for the considered MPPT methods and associated static characteristics are presented and commented on, and the most promising MPPT methods for the considered system were determined by comparing the obtained results.

Abstract: Solar power plants are most often connected to the distribution system, and their use leads to a load on the power grid in terms of voltage stability, frequency stability, voltage harmonics, etc. This thesis examines the values ​​of the electricity quality parameters of the FESB solar power plant, in order to determine whether the parameters are within the permitted limits prescribed by the Croatian standard HRN EN 50160 and the Grid Rules of the Distribution System. The second chapter describes in general terms the quality of electricity defined by the HRN EN 50160 standard and the Grid Rules imposed by the distribution system operator. Electricity parameters are important indicators that determine its quality. In the event that one or more parameters are not met, and the most common cause may be the consumer, the power system is subject to a disturbance or/and system breakdown, and therefore the third chapter describes in detail the electricity quality parameters that need to be aligned with the HRN EN 50160 standard. The fourth chapter describes the FLUKE 435 device, the parts of which it consists of, and the function for using the device. In the last chapter, the values ​​of the parameters of the FESB solar power plant were tested using the FLUKE 435 device. First, the design of the FESB solar power plant was described, and then the testing of the mentioned parameters was started. Indicative values ​​of the parameters were obtained, which were graphically displayed and subsequently used to approach the analysis of the quality of electricity, in accordance with standards and regulations.

Abstract: In this thesis, the basic properties of PV cells are first described. By connecting PV cells, usually in series, a PV module is obtained, whose lifetime is typically 25 years. With PV systems, it is important that the cells are correctly connected to meet the voltage and current requirements and that they are protected from atmospheric influences. Then the ideal PV model with current source and diode as well as the photoelectric effect is described. Since power electronics converters are responsible for most of the power losses in a PV system, methods to improve PV system efficiency are also clarified. The basic requirements for connecting the PV source to the grid and protection are regulated by international standards, with islanding protection being perhaps the most technically demanding since the inverter must disconnect the PV system from the grid in a very short time after the grid is turned off. Converter topologies for connecting PV modules to the power grid consist of power optimizers and microinverters. As for the string exchanger, all processed topologies use the bridge topology (H-bridge) as a starting point and represent its upgrade. Central exchangers are explained using NPC topology. The methods of synchronization with the grid using Fourier analysis and using a phase-locked loop, which provides information about the phase angle and amplitude of the grid voltage, are also explained. The basic structure of the phase-locked loop, its block diagram and response are presented, and the corresponding key parameters are given.

Abstract: This thesis describes the working principle of the lead-acid battery and the associated basic definitions and features. The division of the mathematical models of the battery is presented, and the battery models based on the replacement circuit are additionally explained. Furthermore, battery charging and discharging experiments were performed and, based on the conducted experiments, the characteristics of the dependence of SOC of the batteries on the idle voltage were determined. These characteristics were determined experimentally in the range of SOC 30% - 100% with a step of 10%. After that, the parameters of the lead-acid batteries were determined for various associated mathematical models based on the alternating current circuit, which are available from the literature. For the purpose of determining the parameters of the model, battery voltages were recorded during the experiments, which included battery idle, discharge, charge and rest after discharge and charge to record the dynamics of the battery for all typical operating modes. Such demanding and long-term experiments are necessary in order to calculate the exact values ​​of the parameters, and the model has satisfactory performance. Experimental tests were carried out on two new and one older battery, where the newer batteries were from the same production series, while the older battery was from a different production series. Finally, based on certain parameters and characteristics of the batteries, corresponding simulation models were created in the MATLAB-Simulink software package, where the current measured during the experimental experiments was used as an input variable for a better comparison of the simulated voltage with the real one. To compare the accuracy of the considered models, the integral of the absolute error between the simulated and real voltage was used. In the last chapter, the results of different battery models were analyzed with accurately calculated amounts of model parameters at different percentages of SOC. On the basis of this analysis, the most accurate model was chosen, and the results with approximate parameter values ​​were additionally analyzed for it.

Abstract: In the theoretical part of the paper – in the second and third chapters – the operating principle is described and the basic equations of the system components (photovoltaic source, batteries, transformer, PI regulator, step-up DC converter and single-phase bridge inverter) are given, along with an explanation of the concept of unipolar and bipolar PWM modulation. Simulation models of the system components created in MATLAB Simulink are also described. The selection of parameters and the corresponding system component menus are presented. The fourth chapter includes simulation analysis and comments on the obtained results, starting from a simpler system configuration to a more complex one, in order to better understand the influence of individual components and changes in the corresponding parameters on the system behavior. The simplest configuration consists of batteries, inverters and loads. Within this configuration, the adjustment of the PI voltage regulator parameters of the loads is explained and the minimum number of batteries for the linear operating range of the inverter is determined. The initial configuration was upgraded with an inductive filter, whose inductance was determined by trial and error with the aim of keeping the THD of the load voltage below 5%, for unipolar and bipolar PWM modulation. The considered system was further upgraded with an ideal transformer, in order to raise the voltage level of the inverter output voltage. The final configuration of the island photovoltaic system consists of a PV source, a step-up DC/DC converter, batteries, inverter, inductive filter, transformer and loads. After determining the settings of the reactive components of the step-up converter and adjusting the parameters of the PI voltage regulator of the PV source, the impact of changes in insolation and temperature of the PV source and load power on the system power balance (i.e., on battery charging and discharging), with a fixed PV voltage, was analyzed. Finally, the impact of the battery SOC on the system operation was analyzed

Abstract: Achieving sustainable energy development implies investing in renewable sources of electricity such as photovoltaic power plants, wind power plants, hydroelectric power plants, etc., which greatly contribute to reducing the negative impact on the environment. As part of this work, a photovoltaic power plant project was developed for the production facility of the Aluflexpack Novi d.o.o. factory, which consists of several separate buildings defined by different slopes, roof dimensions and certain objects on the roof itself. The design included the creation of a power plant model using PVSOL Premium software, the calculation of voltage conditions, the determination of lightning protection, the calculation of the energy balance, the definition of the bill of quantities and the creation of drawings using AutoCAD software. All electrical installation equipment and accessories are of a quality, characteristics and properties in accordance with the applicable technical regulations and rules. The first and second chapters elaborate on the general characteristics of photovoltaic systems as well as the selection of photovoltaic modules and inverters. The third chapter presents a technical description of the considered production facility of the investor Aluflexpack Novi d.o.o. and the creation of a 3D model on which the design was based. The fourth chapter presents the necessary calculations that satisfy the various technical conditions according to which the equipment was selected.

Abstract: In this thesis, the Croatian standard HRN EN 60909-3 is described in detail, and examples of calculations in the NEPLAN program are given in accordance with the used standard. The third part of the HRN EN 60909 standard describes the procedures for calculating currents during two separate simultaneous earth faults in systems with an isolated or resonantly grounded constellation, as well as the calculation of partial currents through the ground in case of a single earth fault in rigidly grounded or low-ohmic grounded systems. In the second chapter, the currently valid Croatian norms HRN EN 60909 are listed. Definitions of the sizes used for the purposes of this standard are described and the corresponding formulas are given. In the third chapter, the initial symmetrical short-circuit current, the shock (peak) short-circuit current, the interrupting symmetrical short-circuit current and the permanent short-circuit current are described. The distribution of earth fault currents during two separate simultaneous earth faults is described and relevant examples are given. The fourth chapter describes the partial currents through the ground in case of an earth fault in the substation, outside the substation and in the vicinity of the substation. The calculation of the reduction factor for overhead lines with protective ropes is also described. The fifth chapter describes the calculation of the reduction factor and current distribution in the case of a cable with a metal jacket (shield) grounded at both ends. The case of a three-core cable and three single-core cables was considered. In the sixth chapter, the NEPLAN program is described, which was used for three examples where two separate simultaneous single-phase short circuits were performed. Examples of the calculation of partial currents through the ground in the event of an earth fault in a substation and an example of the calculation of the reduction factor and distribution of currents through the ground in the event of an earth fault in a substation powered by a three-wire cable are also presented, taken from the HRN EN 60909-3 standard.

Abstract: The paper presents work with the Siemens DIGSI 5 software package, using the example of a numerical relay device for differential protection of a power transformer, as an introduction to the use of digital twin technology for the virtualization of numerical relay devices in the cloud. The method of parameterization of the aforementioned relay device using the DIGSI 5 program is described in detail. In addition, the method of its testing, which was performed using the Omicron CMC test device, is also presented.

Abstract: The task of this thesis was to study the frequency-dependent model of a metal oxide surge arrester developed by the IEEE working group 3.4.11. and its implementation within the EMTP – RV software package. ABB’s EXLIM T surge arresters were successfully implemented within the software package. The theoretical basis of the IEEE frequency-dependent model of a surge arrester is described in the introductory part of the paper and in the second chapter. The stages of development and the final version of the model are described, along with the equations through which the values ​​of the parameters of individual model elements are obtained. The second chapter also describes in detail individual model elements within the EMTP – RV software package, and among other things, their capabilities and impact on simulations are listed. The third chapter contains catalog data for 28 EXLIM T metal oxide surge arresters. The tables list the surge arresters according to the maximum system voltage and the nominal voltage. The maximum residual voltage on the surge arrester during current surges of different duration and intensity is listed. The third chapter also includes catalog data on the dimensions of individual surge arresters as well as illustrations of their shapes. The process of modeling a metal oxide surge arrester within the EMTP – RV software package is described in the fourth chapter. A detailed procedure is described using the example of just one surge arrester with a nominal voltage of 444 kV. The procedure starts with the selection of the necessary model elements, followed by the calculation of parameter values ​​and their entry into individual elements. After the first iteration of the model is completed, the simulation is started and, by adjusting the element parameters, the most accurate model of the surge arrester is attempted to be achieved. For other surge arresters, a detailed procedure is not provided, but numerical simulation results and changed model parameters are presented in a table. The fourth chapter also presents the Heidler function with its associated parameters. Finally, the fifth chapter analyzes the obtained values ​​of the surge arrester model parameters with the aim of developing a method that would allow the same solution to be achieved in future surge arrester modeling using an accelerated procedure. The adjustment time of the Vref parameter for the slow wave and the adjustment time of the L1 parameter for the fast wave are successfully shortened by developing equations that relate the aforementioned parameters to the residual voltage on the surge arrester.

Abstract: This paper describes the theory of reliability, the application of network rules to obtain reliability indicators, the basics of the NEPLAN program, and reliability analysis, illustrated by an example of obtaining reliability indicators in the NEPLAN program. The second chapter discusses reliability in power systems, how reliability is predicted, what reliability indicators are in the theory of reliability itself, and how to obtain them for non-repairable and repairable elements. Every power system must fulfill the task of ensuring reliable and constant power supply to its consumers, therefore operators (service providers) of distribution and transmission systems must fulfill network rules. With regard to network rules, general and individual reliability indicators are determined, as described in the third chapter. In subsequent chapters, the NEPLAN program is described, how to create certain schemes, how to enter data for elements, and how to obtain results. After that, an example in the NEPLAN program is shown, which shows the basic parts of the main circuit diagrams, in which a reliability analysis was performed. Based on the reliability analysis in the NEPLAN program, tabular and graphical results are obtained, which show reliability indicators for each individual element in the system and for the system as a whole.

Abstract: The task of the thesis was to model a high-voltage network and conduct a detailed analysis of the overvoltage protection of a power transformer due to a lightning strike using the EMTP-RV software package. When modeling the network, the principles and requirements of the profession were respected. The lightning strikes that were used to simulate a lightning strike are standardized values. The first, introductory chapter provides an overview of the thesis task and describes the software package in which the given problem will be solved. The considered scenario is also briefly outlined. The second chapter of the thesis provides an overview of all scenarios that are modeled in the EMTP-RV software package. It also describes the method of modeling lightning current using the Heidler function recommended by the HRN EN 62305 standard set. The third chapter of the thesis describes all the main elements of the equivalent circuit of the considered scenario in the EMTP-RV software package. An attempt was made to use ready-made elements that are available in the library of the relevant software package as much as possible. Some elements, such as surge arresters, are modeled using more complex methods that require combining multiple available blocks to obtain a functional block. The fourth chapter of the thesis provides a detailed insight into the behavior of the network due to lightning strikes on the protective cable at specific locations. Conclusions are drawn based on the analysis of where it is best to position the surge arresters themselves. At the end of this chapter, the spark gaps themselves on all thirty poles, which conducted the current, depending on the location and shape of the lightning, are also analyzed.

Abstract: This paper analyzes different types of relay protection devices used to protect components in the power system. In addition to theoretical analysis, these devices are shown on the example of protecting a 110/30 kV substation. Using the DIGSI 5 software package from Siemens, the work with protection devices and the principle of their optimization are shown. At the beginning of the paper, the most important protections used in distribution networks are described. The main division is into overcurrent protection and power transformer protection. The area of ​​application of all protections is stated, in which types of faults occur, and their advantages and disadvantages. The third chapter of the paper refers to the comparison of various 7SJ8x and 7UT8x type protection devices. The differences between them and the area of ​​application for which they are intended are stated. The end of the paper itself and the most important part is dedicated to the description of the procedure and parameterization of all protection devices used to protect a 110/30 kV substation with 5 bays. Three protection devices 7SJ82, 7SJ85 and 7UT85 were used to protect this plant. These are devices of the last generation SIPROTEC 5 of the Siemens brand, which are currently one of the most modern and sophisticated devices for relay protection on the market.

Abstract: Switching overvoltages are the main sources of disturbances in power plants. Switching overvoltages occur during the switching and/or switching of switching devices. This paper provides theoretical background on switching overvoltages, insulation coordination, ATP software package, Gaussian and Weibull distributions. It also describes the procedures for analytical and numerical calculation of voltage probability distributions. The paper presents a statistical analysis of switching overvoltages in the power system, using the Monte Carlo method and numerical simulations of overvoltage conditions using the ATP-EMTP software package. The analysis of the simulation results of different models explains the influence of the number and position of surge arresters on the probability of voltage magnitudes. The obtained results can help in the statistical method of insulation coordination. The data obtained by mathematical and numerical methods are compared. Based on the obtained results, it can be concluded that the Weibull distribution can predict the probabilities of overvoltage magnitudes.

Abstract: The thesis deals with risk analysis when designing a lightning protection system using the HRN EN 62305 standard. The paper presents a procedure for calculating the risk in the event of a lightning strike on a building that is planned to be protected and the supply line connected to the building or in the event of a lightning strike next to the building in question and next to the supply line, in order to determine the need for protective measures. The calculation procedure includes an estimate of the annual number of hazardous events, an estimate of the probability of damage and an estimate of the amount of losses. The above calculation procedure and risk analysis were carried out on the example of an office building. The conclusion on the necessity of installing a lightning protection system is based on a comparison of the obtained risk results with the acceptable risk values ​​specified in HRN EN 62305.

Abstract: Distance protection is the basis for protecting high-voltage lines in the 400, 220 and 110 kV transmission network from the occurrence of various types of faults. Its role in the power system is given in the introductory chapter of this thesis, as well as the consequences it has in affecting the basic functions of the system. Knowing the conditions that a distance relay should meet in the network is of essential importance, and it is worth mentioning the speed of operation, selectivity, sensitivity and backup protection. The second chapter describes the basics of implementing distance relay protection in the system, its basic principles, methods of connection to a high-voltage transmission line via current and voltage transformers, and the different types of operating characteristics that such a relay can have. The third chapter explains the structure of the microprocessor electronic circuits on which the modern Siemens Spirotec 7SA6 distance relay is based, and the characteristics of this device are analyzed in detail, along with descriptions of all its functions in the network. The fourth chapter discusses the principle application of the ATP-EMTP software, which is used in modern times for various types of analysis of the power grid, and especially for the analysis of various types of faults in the grid (short circuits, lightning strikes, etc.). The basic principles of use and the methods of mutual communication of the program modules are also explained. The fifth chapter describes the application of the ATP-EMTP software, specifically by simulating various types of short circuits in the high-voltage transmission grid (single-pole, double-pole and three-pole short circuits) and by analyzing the tripping distance protection with a polygonal tripping characteristic with three protection zones in relation to these faults. Short circuits were simulated at different locations on the protected line section and the trajectories of the measured impedances in all three phases in the R-X coordinate plane (Argand diagram) are shown.

Abstract: This thesis describes the properties and capabilities of the XGSLab software package and its modules. The goal was to independently calculate the magnetic field strength in this software package, study its applications and describe its use. The second chapter describes the properties of the electromagnetic field according to Maxwell’s equations in differential form. Furthermore, the magnetic field of an electric current and the quantities that describe it are explained in more detail. Then, the effects of magnetic fields on humans according to Directive 2013/35/EU of the European Parliament and of the Council are described. The main physical quantities and regulations that must be observed according to the Ordinance on Protection against Electromagnetic Fields are also listed. The tables give the limit values ​​of magnetic field strength and magnetic flux density for public areas and areas of increased sensitivity. The third chapter contains a detailed description of the XGSLab software package: its modules GSA and GSA_FD for calculations of grounding systems, XGSA_FD for analysis of overhead and underground grounding systems in the frequency domain, XGSA_TD for analysis of overhead and underground grounding systems in the time domain and NETS for calculation and simulation of multi-conductor and multi-phase complex networks. The areas of application of this software package, its applications and capabilities are listed, starting from standard references, waveform, soil modeling, up to data analysis and display of results. At the end of this chapter, the calculation of the magnetic field strength is described and already solved examples of the distribution of magnetic induction in space for various elements of the power system in the XGSA_FD module are shown. The fourth chapter solves examples of the calculation of the magnetic field strength, or magnetic induction using the XGSLab software package for a three-phase overhead line and cable. All the steps necessary for successful execution of the calculation are listed and the obtained results are shown.

Abstract: In this doctoral dissertation, a 3D exact harmonic electromagnetic model of an infinitesimal thin-wire conductor (ITV) in a horizontally layered multilayer conductive medium, consisting of air and multilayer soil, has been developed. Based on this 3D exact electromagnetic model, a 2D exact harmonic electromagnetic model of an infinitely long insulated thin-wire conductor (BDITV) has been developed, as well as a 2D exact harmonic electromagnetic model based on it for calculating the self and mutual longitudinal unit impedances of rectilinear mutually parallel BDITVs in a horizontally layered multilayer conductive medium, consisting of air and multilayer soil. The 3D exact harmonic electromagnetic model of the ITV contains numerically demanding 3D Sommerfeld integrals, while the 2D exact harmonic electromagnetic model for calculating the self and mutual longitudinal unit impedances of rectilinear mutually parallel BDITVs contains equally numerically demanding 2D Sommerfeld integrals. In the theoretical development of the 3D exact harmonic electromagnetic model of the ITV, in order to more easily satisfy the boundary conditions, the arbitrarily oriented ITV is decomposed into two components: a vertical infinitesimal thin-wire conductor (VITV) and a horizontal infinitesimal thin-wire conductor (HITV). From the general solutions of the Helmholtz equations for the components of the vector magnetic potential of the VITV and HITV and the boundary conditions, systems of linear equations were obtained, in which the unknowns are the kernels of the spectral Green’s functions of the VITV and HITV. By very demanding analytical solution of these systems of linear equations, analytical expressions for the kernels of spectral Green’s functions of the vector magnetic potential components of VITV and HITV were originally obtained, and from them, analytical expressions for the kernels of spectral Green’s functions of the scalar electric potential, electric field strength components and magnetic induction components of an arbitrarily oriented ITV in a horizontally layered multilayer conductive medium were obtained. The total number of soil layers, the layer in which the source is located and the layer in which the observation point is located are completely arbitrary. 3D Sommerfeld integrals connect the spatial and spectral Green’s functions of Lorentz potentials, electric field strength components and magnetic induction components of ITV. In the theoretical development of the 2D exact harmonic electromagnetic model of the BDITV parallel to the ground surface, the spatial Green’s function of the vector magnetic potential of the BDITV in a horizontally layered multilayer medium was obtained by integrating the spatial Green’s function of the horizontal component of the vector magnetic potential of the HITV along the BDITV axis. In this way, a 2D exact electromagnetic model of the BDITV was obtained from the 3D exact electromagnetic model of the HITV. In the electromagnetic model of the BDITV, instead of 3D Sommerfeld integrals, 2D Sommerfeld integrals appear, while the spectral Green’s functions of the vector magnetic potential of the BDITV and the horizontal components of the vector magnetic potential of the HITV are identical. From the originally developed 2D exact harmonic electromagnetic model for calculating the self and mutual longitudinal unit impedances of rectilinear mutually parallel BDITVs in a multilayer horizontally layered medium, with some neglects, the generally known Carson and Sunde formulas for calculating the self and mutual longitudinal unit impedances of rectilinear mutually parallel BDITVs in a two-layer horizontally layered medium, consisting of air and homogeneous soil, were obtained. In this doctoral dissertation, numerical algorithms for the numerical calculation of 3D and 2D Sommerfeld integrals were also originally developed, which are based on a combination of polynomial interpolation of spectral Green’s functions by parts of the integration curve and analytical integration. In addition, the existing Mosig-Michalski algorithm, which was developed for calculating 3D Sommerfeld integrals for a horizontally layered multilayer ideal dielectric, was modified and adapted to the peculiarities of 3D and 2D Sommerfeld integrals in the case of a horizontally layered multilayer conductive medium, consisting of air and multilayer soil. Numerous numerical tests have shown that both numerical algorithms efficiently and with high accuracy calculate the numerically demanding 3D and 2D Sommerfeld integrals for a wide range of variable parameters.

Abstract: This thesis studies the characteristics and possibilities of using the computer program NEPLAN in engineering practice and for teaching purposes, with a special emphasis on the short-circuit analysis module. NEPLAN is an extremely powerful software tool used to perform analyses and calculations of various network states. The program allows parameterization of elements down to the smallest detail, and the calculations are performed at high speed. Detailed modeling of system elements ensures this program high accuracy even with many elements in the system. The NEPLAN V553 version of the program was used in this paper. After the introductory part, the basic characteristics of short circuits according to the HRN EN 60909 standard are described. An overview of the basic formulas required for calculating the equivalent impedances of electrical elements required for calculating short-circuit currents is given. This chapter of the thesis also describes the basic components of short-circuit currents. A description of the symmetrical components for the four basic types of short circuits and short circuits through fault impedance is also given. The third chapter describes the general part of the NEPLAN program, the appearance of the graphical user interface, and the method of data management in the program. The program modules that are most often used in the program are also described, with special emphasis on the short circuit analysis module. The fourth chapter follows, in which the method of parametrizing the elements and performing the simulation necessary for the calculation of short-circuit currents is described. In the fifth chapter, an example of three-phase and single-phase short-circuit analysis on selected buses of a given network is given in the NEPLAN program. In order to verify the accuracy of the results in the NEPLAN program, the calculation of the short-circuit currents on the same network was also performed in the PowerCAD program.

Abstract: The task of this thesis was to analyze in detail the effective length of the simplest version of the type A grounding system in accordance with the HRN EN 62305 standard set during a lightning strike to its central point. In the thesis, the grounding system considered consists of two opposing elementary grounding conductors and is buried parallel to the ground surface in homogeneous soil. The second chapter describes the main features of the type A grounding system in accordance with the HRN EN 62305 standard set. The version of this grounding system used in this paper, which consists of two opposing horizontal elementary grounding conductors, is also described. The third chapter defines the concepts of impulse impedance of the considered grounding system and effective length of the grounding system. The fourth chapter describes the EMGround program that was used to obtain the most accurate values ​​of the effective length of the considered type A grounding system. In addition, the iterative procedure for finding the effective length within this program is briefly described. In the fifth chapter, the influence of the burial depth of the considered grounding system on the effective length for different values ​​of the impulse current wavefront duration and for different values ​​of the homogeneous soil resistivity is analyzed in detail. For eight values ​​of the homogeneous soil resistivity, ten values ​​of the wavefront duration and five values ​​of the burial depth, 400 simulations were performed in the EMGround program in which the effective length was iteratively sought for each case. The analysis of the obtained effective lengths revealed a pattern of similar reduction in the effective length due to an increase in the burial depth, regardless of the values ​​of the wavefront duration and the homogeneous soil resistivity. This influence is described by the factor of reduction in the effective length of the earth electrode due to the burial depth in relation to the effective length of the earth electrode at a depth of 0.1 m. An approximation formula for the mentioned factor was developed in MATLAB’s Curve Fitting Toolbox and its accuracy was confirmed in the same chapter. In the sixth chapter, ten values ​​of the resistivity of homogeneous soil and ten values ​​of the wavefront duration were selected and the effective length of the considered grounding system at a burial depth of 0.1 m was calculated using the EMGround program. It was shown in the previous chapter that the obtained effective lengths can be converted to other burial depths using the factors developed in that chapter. By analyzing these one hundred obtained effective lengths, four approximation formulas were developed that can quickly and accurately calculate the effective lengths of the considered grounding system for any combination of parameters within the prescribed intervals. In the seventh chapter, two short numerical examples are given in which practical examples of calculating the effective length of a type A grounding system for different parameter values ​​are presented.

Abstract: This work introduces the need for the implementation of dynamic power network reduction. The current state of the art reveals the main interest is in three different reduction methods. Those are namely neural networks, system identification, and equivalent generator. By implementing specific algorithms, each procedure shows the capability of reproducing certain variables of the system. That enables dynamic reduction for the particular part of the system. The results show sufficient reduction with neural networks and system identification model. Still, the equivalent generator model shows somewhat worse results. Each method is trained and validated with specifically defined scenarios. The ending chapters present all of the results with valid comparisons in parallel.

Abstract: This paper elaborates the idea of ​​regulating the voltage of a transmission line using an SVC plant. It explains which principles should be applied if the voltage level is lower or higher than the required level. The paper provides a detailed analysis of the voltages and currents of the TCR and TSC, supported by appropriate mathematical derivations. Furthermore, the SVC plants used for the purpose of regulating the voltage level, as well as their basic components and characteristics, are discussed in more detail. An insight into the basic designs of SVC plants is given, the justification and cost-effectiveness of choosing a particular design of SVC plant, and their advantages and disadvantages. It explains how individual SVC plants regulate the voltage level. A detailed harmonic analysis of the waveforms of the voltages and currents of the components that make up the SVC plant is made, and how to minimize the negative impacts of the operation of the SVC plant. The SVC plant can have several applications, and from the network side it represents a variable susceptance. The name static Var compensator comes from the fact that such a plant does not contain rotating parts. The introduction provides an overview of the need for the use of SVC plants, while the second chapter discusses the method of voltage level regulation. The basic configuration of the SVC plant is given in the third chapter, while the fourth chapter briefly describes the basic components, or parts of the SVC plant, with special emphasis and detailed development of thyristor-controlled chokes (TCR) and thyristor-switched capacitors (TSC). The fifth chapter discusses the most common designs of SVC plants in use today. It also presents diagrams of the reactive power exchange of the SVC plant with the network, and therefore the operating modes in which the SVC plant can operate.

Abstract: The task of this thesis was to describe limited earth fault protection and to make its application on a concrete example using the RET670 relay from ABB. The 16/121 kV power transformer block in the Zakučac HPP was chosen as an example of setting up the protection. The first chapter of the paper contains an introduction, the second chapter describes the principle of operation of the power transformer, its parts and basic data. The third chapter describes current transformers for protection as well as their basic data through which the transformer for a particular protection is selected. The fourth chapter describes limited earth fault protection (REF, 87N) which is of a differential nature. The principle of operation of the protection and the connection schemes for two-winding and three-winding transformers, autotransformers and chokes are generally presented. The fifth chapter lists the functions of the RET670 numerical relay, its appearance and dimensions, and shows tables through which REF protection is set, as well as the algorithm of limited earth fault protection used by ABB relays. In the last, sixth chapter, the calculation through which the current transformers for protection and the REF protection settings were selected is presented. The attachment at the end of the work shows the REF protection settings from the PCM600 program.

Abstract: Remote protection is the basic protection of high-voltage transmission networks, which are mostly complex and looped and fed from several sides. The operating time of remote protection depends on the distance of the installation point of the remote relay from the location of the fault. The remote relay is connected to the current and voltage transformers, so it measures the current and voltage and determines the impedance based on their ratio. Argand’s diagram, k-circles, ψ-circles, orthogonal trajectories and conformal mapping, mathematical expressions that are useful for any type of protective devices and are also necessary for remote relays, are analyzed in this thesis. For the analysis of the measured impedance, fictitious substitute systems were used to show the occurrences of phase-to-phase short-circuits and short-circuits to earth. Interphase short circuits include three-pole and two-pole short circuits, while short circuits with earth include single-pole short circuits and two-pole short circuits with simultaneous earth connection. The most adequate way of observing the measured impedance seen by the relay at the place of installation of the relay device is the graphical representation of the impedance in the complex Argand plane.

Abstract: Remote protection is the basis of network protection in transmission systems, as well as in interconnected distribution networks. Its operating principle is based on the measurement and assessment of the short-circuit impedance, which in the basic case is proportional to the fault distance. Testing the remote protection function is the main topic of this work, where hardware (test set CMC) and software (Test Universe) from Omicron, and relays 7SA611 from Siemens were used. Two types of tests were carried out in this work, basic and advanced. Basic testing was performed using the QuickCMC, Advanced distance and State Sequencer modules. Through basic testing, we evaluate the behavior of the remote protection function of a relay isolated from the rest of the network, using the three previously mentioned modules. On the other hand, we have a test using the RelaySimTest module, which is considered a more advanced test. RelaySimTest offers the possibility of managing multiple test sets over the Internet, which requires at least two computers with Internet access, one at the local end and the other at the remote end. The local computer is running RelaySimTest, while the computer at the remote end is running Device Remote Agent, which creates a network connection and assigns control of the test set to RelaySimTest. What is being tested in this paper is the protection of a transmission line using two 7SA611 numerical relays. The test sets are Various failures are simulated, and we use modules to evaluate the passability of the tests performed.

Abstract: In this paper, theoretical bases on the Sun, its motion and solar radiation are given. The procedure of analytical calculation of solar radiation for a specific location and also for determining the optimal angle of inclination of photovoltaic modules at a specific location is also described. A detailed analysis of the geographical parameters of a particular location gave us the necessary knowledge about the dependence of the geographical position of the location and the associated solar radiation. Using the software PVsyst, the operation of the photovoltaic power plant was simulated and the calculation of the annual production for different angles of the photovoltaic module was performed. The analysis of the results of production simulations explains the influence of the angle of inclination of photovoltaic modules on the production curve and on the total amount of production of a solar power plant. Using the available tool, the optimal angle of inclination of the module was also calculated. Also, to investigate the impact of using the Sun tracking system, production simulations were conducted with their use. It has been concluded that Sun tracking systems are a relatively new technology that will develop and in some parts of the Earth they are very likely to find future use.

Abstract: This paper analyzes the cost-effectiveness of building a small hydropower. The term small hydropower is considered to be all hydropowers with a capacity of 1-10 MW. The first part of the paper describes the parts of the hydropower plant in two groups: civil works and electromechanical parts. Civil work includes structural parts such as dams, devices to raise the water level, spillways, intake structures and penstock. A more complex group of small hydro parts includes a turbine and a generator. By choosing the right turbine, the cost-effectiveness of small hydro is higher. Small hydro-turbines can achieve efficiency up to 90%. The type of small hydro is selected depending on the terrain on which it is built, and they can be: run-of-river schemes, site configurations, schemes with the powerhouse at the base of a dam, schemes integrated with an irrigation canal. The final design solution of the small hydro is obtained as a result of a complex and interactive process, where, taking into account the impact on the environment, different technological possibilities are always compared, also taking into account the cost side of the project. The paper develops software for the analysis of annual electricity production from hydropower and cost-effectiveness analysis based on substrates defined by RETScreen software. Hydrological data are usually defined by a flow duration curve, which is assumed to represent conditions during the average hydrological year. Production from small hydropower in the mentioned model was determined on the basis of data on available, designed and residual flow, and on the basis of load, gross head and efficiencies/losses. Turbine efficiency can be entered manually if data are known or approximate expressions are used depending on the type of turbine and its basic parameters. Power available as a fuction of flow, capacity factor, total delivered energy, estimation of plant capacity - are calculated by given model equations, while the power duration curve is defined from the flow duration curve.

Abstract: The distribution network is part of a constantly evolving system. The increase in consumption and connection of new consumers requires network topology redefinition and requires the construction of new substations and distribution network power lines. In most European countries, distribution networks by its topology, is radial. For purposes of network planning, a non-automatic and automatic approach can be used. This thesis defines an automatic approach for distribution network expansion planning, so for this purpose, an optimization model was first mathematically defined, and then implemented in Python. Before the practical part, the criteria considered in the process of network expansion planning as well as the possibilities of its integration in the optimization models are presented.

Abstract: The Photovoltaic Power Profile Emulation (PPPE) software was tested in this thesis. PPPE is software that enables the emulation of photovoltaic panels on programmable DC sources manufactured by Magna-Power Electronics. For a better understanding of the system emulated by the software, a simplified structure of a photovoltaic cell is described and a basic physical description of photovoltaic conversion (photoelectric effect) is given. Basic equations are given that describe the equivalent electrical circuit of a photovoltaic cell. In the PPPE software, there is the option of choosing two technologies for the production of photovoltaic panels. Therefore, in a separate chapter, the technology of manufacturing photovoltaic panels in crystalline silicon and thin film technologies is described with an explanation of the catalog data of commercial panels. The basic technical requirements that a personal computer must meet in order to use PPPE are given and the software installation procedure is briefly described. The program interface is shown and the mode of operation in the software is described in detail. In order to be able to fully use all the possibilities of PPPE, four data entry methods are described, which are used to emulate photovoltaic panels. The software enables emulation of electrical characteristics for different values ​​of temperature and solar radiation of the panel using profiles. Electrical characteristics for a commercial photovoltaic panel Suntech STP190S-24/Ad+ were obtained in Matlab/Simulink, for different values ​​of solar radiation and temperature, using the corresponding block from the Simulink library. Characteristics emulated using PPPE with input parameters of the same Suntech panel were compared with those obtained in Simulink. PPPE was tested in an experiment using a direct current source SL50-30/UI. The experiment used the software’s ability to sequentially change different preset profiles. With the help of the software, either it is possible to sample the values ​​of the emulated electrical quantities. The description of the experimental part shows the time responses of electrical quantities during tests of changes in the input parameters of insolation and temperature, and when the source load changes. Finally, in order to get an impression of where the operating points are located, the corresponding stationary characteristics.

Abstract: In order to decarbonize the energy sector, the share of installed power plants based on renewable energy sources is increasing, as well as new gas thermal power plants in order to support the balancing of the power system. In addition, a relatively new, so-called power-to-gas (P2G) technology is recognized as one of the key factors that will enable the decarbonization of the energy system and help the power system integrate power plants with renewable energy sources. In any case, it is to be expected that the interdependencies of the electric power and gas systems will grow significantly in the coming period. Therefore, it is necessary to have robust simulation models that will efficiently and simultaneously calculate all connected energy networks in only one simulation environment and only one step. As a response to the described computational challenges, as part of the doctoral dissertation, a stationary model of a multi-energy system consisting of connected electric power and gas networks was developed, using the method of electrical analogy. Accordingly, detailed replacement electrical models of gas compressor and metering-reduction stations, as two of the three most important components of gas networks, were developed. The third component is the gas pipelines whose stationary electric substitute model is known in the literature. In addition, in order to simulate the power flows of a multi-energy system, additional electrical substitute models were developed, using the method of network poles, for all three components of the gas networks, as well as for the gas thermal power plant and the P2G plant. The electrical replacement models developed in this way were loaded into the well-known program package for the analysis of power networks - NEPLAN, and in this way the electrical model of a multi-energy system was formed. The accuracy of the developed models of gas network elements was confirmed by comparing the simulation results with the results provided by the well-known commercial program package for the analysis of gas networks - SIMONE, and by comparing them with measurements from a real gas network. In addition, the practicality and advantage of using the applied multi-energy system modeling methodology on the example of security of supply analysis of integrated energy systems is presented.

Abstract: This thesis deals with the regulation of the voltage of a load supplied from a photovoltaic panel using two different DC converters, a step-up and a step-down DC converter. The basic principles of photovoltaic conversion and photovoltaic cells are described, as well as the topology and operating principle of the converters used. Simulation models of the considered systems were created in the Matlab Simulink software package. The basic components of the model are the photovoltaic panel, the DC converter, the control circuit and the load. The load voltage regulation was implemented using a PI regulator. The operating type of the load was used in the simulations. The optimal parameters of the PI regulator were determined by the trial and error method. The responses of the regulated variable to sudden changes in the associated reference value and to the occurrence of disturbances in the system in the form of sudden changes in insolation were considered. The paper presents simulation results for both considered DC converters, obtained with previously optimized PI regulator parameters. The system operation was tested at different levels of insolation and load resistance with different constant levels of load reference voltage and PV panel temperature. The tests were carried out for three different PV panel temperatures ranging from 0 °C to 50 °C.

Abstract: This thesis analyzes a photovoltaic system with a DC-DC step-down converter without galvanic isolation, in which three different MPPT methods are used to achieve optimal PV panel power. The basic characteristics of photovoltaic panels, DC-DC step-down converter without galvanic isolation, and some of the most commonly used methods for monitoring maximum power are described. The analyzed system consists of a photovoltaic panel, a DC-DC step-down converter, a control circuit, and a working load and a battery at the output. The PV panel voltage is regulated using a PI controller whose parameters are adjusted by the trial and error method. The effectiveness of the considered MPPT algorithms was tested using a system simulation model created in the MATLAB-Simulink software package. Three simulations were performed, one for each of the considered MPPT methods, covering wide ranges of insolation and PV panel temperatures. For better comparison, the same insolation and temperature values ​​were given in all three cases, at the same time points. Simulation results are presented and analyzed in the last chapter of the paper.

Abstract: In this paper, a simulation analysis of a system for powering a working load from a photovoltaic module via a DC-to-DC converter, in one variant, and a DC-to-DC converter, in the other variant, with load voltage regulation was performed. The basic characteristics of photovoltaic modules were discussed, as well as the influence of insolation and temperature on the electrical characteristics of a photovoltaic cell. Then, the basic characteristics and operating modes of the considered DC-to-DC converters without galvanic isolation were described. A detailed description of the components and parameters of the simulation models of the photovoltaic system with the considered types of converters was given, including the algorithm for regulating the load voltage. The optimal parameters of the PI load voltage regulator were selected using simulation models using the trial and error method. The responses of the regulated voltage to changes in the reference and the influence of disturbances, i.e. changes in insolation, were considered. Finally, the results obtained for both simulation models were analyzed in a wide range of insolation and temperature of the PV panel, as well as for different values ​​of the resistance of the connected load. Special emphasis is placed on comparing the performance of the two considered systems in terms of dynamic indicators of regulation quality, achievable operating range, and ripple of the load voltage and choke current.

Abstract: In this paper, the maximum power point tracking (MPPT) of a photovoltaic module in a system with a boost DC-DC converter and a constant resistance load is analyzed at the simulation level. The maximum power point is tracked using two advanced MPPT methods: the shift and observation method and the incremental conductivity method. First, the operating principle of the photovoltaic cell is described, as well as the influence of temperature and insolation on the efficiency of converting solar energy into electricity. The basic characteristics of the boost DC-DC converter without galvanic isolation and the associated characteristic operating modes are discussed. Then, the operating principle of the MPPT algorithms is described, with special emphasis on the methods used. The model used for the simulations was implemented in the MATLAB-Simulink software package. All components used and their parameters are listed and described. Since a battery is connected in parallel to the load, the voltage at the system output is approximately constant, while the voltage of the PV module is regulated using a PI regulator, with the aim of achieving the maximum power point. The method of selecting controller parameters and MPPT algorithm block parameters for both methods is described. The voltage, power, current and control factor responses for varying insolation values ​​at different constant temperatures are simulated. Finally, the simulation results obtained using both MPPT methods are presented and compared.

Abstract: This paper is based in its first part on basic information about solar energy and photovoltaic systems. The general features of PV modules and PV cells and their current-voltage characteristics are described. Then, the basic characteristics of a step-down DC converter without galvanic isolation are analyzed and its continuous and discontinuous operating modes are explained. In the fourth chapter, the capabilities of the Magna-Power DC source are described, where detailed instructions are given for all its control settings located on the front panel of the device. Since this source can also be controlled via a computer, using a special interface (Remote Interface Software Panel), all associated components are described. After that, the operation of the DC source in the constant voltage (CV) and constant current (CC) modes is shown. The procedure for programming the current-voltage characteristics, which enables emulation of PV modules, is also explained. A laboratory model of the system under consideration is assembled, in which the DC source is connected to a variable operating load via a step-down DC converter without galvanic isolation. Using a model, experimental results were recorded for various examples illustrating the above operating modes of the DC source.

Abstract: In this paper, the operation of a system for stabilized power supply of an active load from a photovoltaic panel via a step-down DC converter without galvanic isolation was analyzed at the experimental level. The voltage regulation of the load was ensured by automatic adjustment of the converter control factor. First, the basic characteristics of photovoltaic modules and the influence of temperature and insolation on the electrical characteristics of a photovoltaic cell are described. The basic characteristics of the step-down DC converter and its characteristic operating modes are listed. Some possibilities of the programmable DC source Magna Power, which can operate in several different operating modes, are also shown. In this paper, the mentioned DC source was used as a photovoltaic panel emulator. A control algorithm was created in the MATLAB Simulink software package and the parameters of the PI regulator were determined. The interface for controlling the experiment in real time was implemented in the ControlDesk software package. A laboratory mock-up of the system with a DS1104 control card (dSpace), an optocoupler as a pulse device for IGBT, and current and voltage sensors is described. The responses of selected system variables to changes in the voltage reference value and changes in insolation and temperature of the photovoltaic panel are shown, as well as the corresponding waveforms in the steady state.

Abstract: In this thesis, the transient analysis of linearly coupled circuits using the finite element method is processed and the methods used for its analytical solution are described. In doing so, Heun’s time integration method and Theta method were used on a selected example of a circuit, and the created program was compared with the numerical simulation results from Simulink. The second chapter discusses in general the methods for harmonic analysis of linear current circuits in the time and frequency domain, of which the most practical method, the finite element method, stands out. The derivation for the branch of the linear coupled circuit for the Heun and Theta method is given in the third chapter and is used in the creation of the user program to define the input data and the mutual relations of the circuit elements. In the fourth chapter, a computer program created in MATLAB and used for linear circuit analysis is described. The aim of the program is to demonstrate the effectiveness of the finite element method in the modeling of circuit elements. In the last chapter, transient analysis is processed on a selected example of a circuit, the Heun and Theta methods are applied, and images of the solutions obtained by the computer program are shown for comparison with the numerical solution from Simulink.

Abstract: The task of the thesis was to develop a theoretical basis and create a computer program for calculating the distribution of electric and magnetic field strengths and current strength for an infinitely long cylindrical multilayer conductor with an arbitrary number of conductive and dielectric layers. Special attention had to be paid to the dielectric layers. Namely, within the framework of this thesis, a theoretical basis was developed for two models of an infinitely long multilayer cylindrical conductor with an arbitrary number of dielectric layers. In one model, displacement currents were completely neglected, while in the other model displacement currents were neglected only in the conductive layers. In addition to the above, it was necessary to consider the calculation of the internal impedance per unit length of such a conductor. The second chapter of the thesis provides an overview of two models of a multilayer cylindrical conductor with an arbitrary number of dielectric layers. The treatment of dielectric layers as well as the designation of geometric and electrical characteristics of individual layers of a multilayer conductor are described. The third chapter of the thesis provides a theoretical basis for calculating the distribution of electric and magnetic field strengths in one layer of a multilayer conductor. This chapter develops a theory for calculating the field in one layer of a multilayer conductor for both cases of taking displacement currents into account. Both developed models of a multilayer cylindrical conductor with dielectric layers are based on Maxwell’s equations for good conductors, which means that displacement currents in the conductive layers are neglected. However, displacement currents are neglected in one model in the dielectric layers, and are taken into account in the other model. The fourth and fifth chapters of the thesis describe the formation of a system of equations from the boundary and boundary conditions between the layers for both models of a multilayer cylindrical conductor with dielectric layers. The sixth chapter describes the calculation of the internal impedance per unit length for both models of a multilayer conductor. The seventh chapter provides numerical examples where the agreement of the results obtained using the two presented models is analyzed in detail. The analysis includes a comparison of the electric and magnetic field moduli along the cross-section of the conductor as well as the calculation of the internal impedance moduli of the multilayer conductor.

Abstract: This paper discusses the basic technical characteristics of a current transformer for measurement and protection. The effects of short-circuit current and its DC component on transients and transformer saturation are presented. Due to everyday use of the electrical network and the need for electricity, a transformer saturation test cannot be performed while the transformer is connected to the network. The saturation effect was simulated in the EMTP-ATP program and MATLAB, where the negative impact of saturation is visible from the graphic display of the transformer secondary current signal. Secondary current distortion directly affects the operation of the connected protection on the secondary of current protection transformers. Transformer saturation needs to be monitored and controlled. In the practical part of the paper, measurements of the basic technical parameters of the current transformer were performed (primary and secondary insulation resistance to each other and to earth, primary and secondary winding resistance, transmission ratio and error, dielectric strength of oil, etc.). The results of each measurement method showed satisfactory transformer properties in terms of its correctness and remaining service life.

Abstract: This thesis examines the characteristics and possibilities of using the computer program PSS/E for teaching and research purposes, with a special emphasis on the short-circuit module. PSS/E is a widely used software for calculations and analysis of various network states, and is characterized by high calculation speed and detailed parameterization of network elements, which makes it very accurate in calculations. The PSS/E Xplore 34 version of the program was used in this paper. After the introductory part, a review of short-circuit calculation is given, with an overview of the physical foundations of short-circuit. A description of the symmetrical component method for short-circuit analysis is also given, with an overview of the basic expressions of direct, inverse and zero order for the four main types of short-circuit, as well as formulas in the case of short-circuit through fault impedance. The third chapter follows a general part about the PSS/E program, its areas of use and program modules that are described individually. The fourth chapter describes the short-circuit calculation itself in the PSS/E program. At the beginning, all options in the short circuit calculation module are presented, followed by general program settings, network creation and parameterization of network elements. Parameterization of the most important network elements is described individually. The chapter concludes with a description of setting parameters for short circuit analysis according to the IEC 60909 method. The fifth chapter follows, which provides an example of a three-pole and single-pole short circuit analysis on selected buses of a more complex test network in PSS/E and a comparison of the obtained results with the results of the same analysis calculated in the IEC 60909 – 4 standard.

Abstract: This paper presents the application of machine learning for the purpose of transformer health analysis. The state of the energy transformer is defined by the health index. Based on classic tests and traditional methods, a certain index was added to each transformer. Insulating oil and its six parameters are tested. Algorithms used to predict the state are: Multinomial Logistic Regression (MLR), Extremely Randomized Trees (ETC), K-Neighbors Classifier (KNN), Random Forests (RFC), Gradient Boosting Classifier (GBC). Finally, the results obtained by machine learning and the results of Fuzzy logic and GRNN were compared. The combination of algorithms in different ensembles led to a high level of prediction accuracy, therefore the presented model could find a place in different self-monitoring and transformer maintenance systems.

Abstract: In the first part of this master thesis basic parts of photovoltaic power plant are described (photovoltaic modules, substations, inverters, prefabricated structures and AC and DC cable distribution) and characteristics of large PV power plants. Through the second part of this work, concept of real large PV plant is defined in few variants and calculation of production and losses are performed. Topology of PV power plant is defined in two basic variants. In the first variant central inverters/substations are positioned in the center of PV modules which are connected on that inverter. In the second variant, central inverters/substations are positioned on the edge of main internal roads as well as on the edge of related group of PV modules. For each variants PV plant topology is defined for the slope of PV modules 15o, 20o and 25o, using Virtuosolar software. Using the PVSyst software net production and losses are calculated for all variants. Analysis of investment costs for the infrastructure, DC and MV AC cables and discounted costs of energy losses in DC cables is performed. It is shown that variant with „central“ positioned inverters/substations is significantly better from economic perspective.

Abstract: The topic of this thesis is parameter selection and application of surge arresters in the distribution network. To begin the work, a description of the basic characteristics of metal-oxide surge arresters intended for installation in the distribution network is given. Their advantages compared to other materials used to make surge arresters are defined. Then, possible voltage stresses that may arise due to the appearance of overvoltage in the network were mentioned. Temporary, switching and atmospheric overvoltages were taken as authoritative overvoltages. For each of the listed overvoltages, different situations of their occurrence were taken. In addition to the aforementioned overvoltage situations, emphasis was also placed on the possible treatment of network grounding, as well as the consequences of the grounding method on the very choice of surge arrester parameters. At the very end, the example of TS 110/20 kV is taken, where the surge arrester is selected for real parameters. The choice of surge arrester is based on the analysis of voltage stresses, processed in the paper.

Abstract: In this paper, several models of transmission poles, grounding devices and insulators are explained, and their characteristic data are given. A simulation was also performed on the 110 kV DV Postire (Brač)-Stari Grad (Hvar) with appropriate models using ATPDraw (Alternative Transient Program), in which atmospheric discharges were simulated into the top of the transmission line pole and into the phase conductor of the transmission line. It is shown how different lightning currents act on the aforementioned transmission line, and how the voltage on the grounding rod of the transmission line pole depends on the steepness of the lightning current front, as well as on the model of the grounding rod and its configuration. The application of different models of insulators is also discussed, and how they have a significant impact on the phenomenon of reverse jump, its occurrence, the moment of occurrence and the resulting amount of reverse overvoltage. It is also shown how important the geometric position of an individual phase on the pole is and the electromagnetic coupling between the phases on the pole as well as the affected phase according to the protective rope, and how important it is at what moment in time the waveform of the phase voltage is found at the time of the lightning strike on the observed phase.

Abstract: The paper presents the method of working with the DIGSI 5 software package, with the use of a numerical relay device type 7UT85 from the company Siemens, when creating a project for adjusting the differential protection of a two-winding power transformer. In addition to differential protection, low-adjustable and high-adjustable overcurrent protection and thermal protection of the transformer have been implemented. When adjusting the differential protection parameters, additional stabilization and cross-blocking functions were used, as well as the blocking of action when engaging in idling (detection of the 2nd harmonic) and overexcitation of the transformer (detection of higher harmonics). The work with the DIGSI 5 program when connecting the relay device to current transformers, as well as the method of implementing the signal and switching matrix, is presented in detail. Input data on the specific two-winding power transformer from the distribution network were used.

Abstract: This paper describes the design of a three-phase calibrator, i.e. generator of voltage and current signals. The core of the calibrator is an IGBT converter with a low-pass LRC filter at the output, which eliminates higher voltage and current harmonics. The modulation technique used to control the IGBT conduction process is sinusoidal pulse width modulation (SPWM). Amplitudes and phase angles are regulated to compensate for system nonlinearity, temperature changes, voltage drops on parasitic components, etc. The implemented algorithms serve to generate the SPWM signal that will be controlled by the IGBT bridge. The processor with FPGA technology (Programmable Logic Gate Arrays) enables very high speeds of digital signal processing. The speeds that the FPGA processor itself achieves in parallelism are in the nanosecond range. The experimental results show the great potential of the proposed method for the design of calibrators for various electrical measuring instruments.

Abstract: Due to the high cost of replacing a power transformer, more and more attention is being paid to its monitoring and preventive maintenance. The first chapter provides an introduction to the issue of transformer insulation condition analysis, and offers a solution in the form of a unique value that describes this condition. We call this value the health index. This chapter also provides the main causes of transformer failures, and the components that are most affected by them. Finally, the fault diagnosis tests and their frequency are listed. The second chapter of this paper describes the parameters that most affect the health index of a power transformer. This group of parameters includes the analysis of dissolved gases, furan compounds, oil breakdown voltage, dielectric loss factor, water content in transformer oil and total acidity of transformer oil. The basics of artificial neural networks, together with the theory of predictive modeling, are described in the third chapter. Special attention is paid to the backpropagation algorithm, and classification and regression predictive modeling. The fourth chapter presents the analysis of the health index using the MATLAB software package and its built-in tool for creating artificial neural networks NNTOOL. The analysis was performed on a group of 50 transformers, whose input parameters and health indices were taken from the literature. After that, the results of the artificial neural network were compared with those taken from the literature, and the accuracy of the neural network in predicting the new value of the health index for transformers that were not used during its training was confirmed. The fifth chapter presents a conclusion on the results of the application of artificial neural networks in the analysis of the energy transformer health index.

Abstract: The paper describes the development and construction of a firewood cutting device. The introductory part of the paper presents the type of logs that are intended for cutting with a device of this type. Patents and existing devices on the market are also investigated. After that, a functional decomposition was made, based on which 4 concepts of firewood cutting devices were created. The concepts were evaluated based on criteria that emerged from the market and demand analysis. A morphological matrix was created for the best concept, showing possible solutions for each function. Finally, a control calculation was made and the necessary dimensions of machine parts and standard components of the device were selected. Based on the calculation and standard parts, a computer model and technical documentation of the device were created.

Abstract: In this doctoral thesis, an advanced numerical model for the analysis of angular stability in the power system (PS), which is based on the finite element technique and time-varying phasors, has been developed. The complex numerical analysis is simultaneously performed in both the time and phasor domains. The developed numerical model, unlike existing programs for the analysis of angular stability that are limited to the analysis of transient stability during the first quarter of the period, can analyze the entire transient phenomenon. The basis of the developed numerical model for the analysis of angular stability in the PS is the application of the finite element technique to the PS so that the considered system is divided into smaller parts, which are treated in the calculation process as separate finite elements with a certain number of local nodes. As the most important part of the power system, in the first step, a subtransient numerical model of a synchronous generator with an appropriate system of algebraic equations has been developed, which is defined and treated as a finite element with three local nodes. The developed numerical model of a synchronous generator for the analysis of angular stability in the power system includes the originally developed numerical model of a digital turbine controller as well as the originally developed numerical model of a digital voltage regulator. Also, based on the appropriate mathematical models, numerical models of other parts of the power system (transformers, lines, equivalent network) were developed, which were treated as separate finite elements in the calculation process. The accuracy of the developed numerical model for the analysis of angular stability in the power system was confirmed by comparing the calculation results with the results obtained using the EMTP software package. The proposed numerical model enables a very simple and fast analysis of the angular stability of a large power system.

Abstract: This paper describes the short circuit calculation method in matrix form. In the first part of the paper, the types of short circuits were theoretically explained and expressions were obtained for short circuit currents and voltages after the failure, assuming that the voltage before the failure was 1 p.u. When calculating, it is important to know the impedance values ​​of the circuit elements due to the formation of the node impedance matrix. We have broken down the currents and voltages into their symmetrical components and thus made the calculation easier. In the second part of the work, for the analysis of short-circuit currents, we used Matlab in which we entered data, formed the node impedance matrix and calculated short-circuit currents using theoretically obtained expressions. Finally, on the example of the electrical network, a comparison was made of the obtained results for currents through the branches and voltages on the busbars, obtained with the help of Matlab, with the results obtained with the help of Powercad. From the attached tables, we can see that there are no excessive deviations in the results.

Abstract: The quality of a certain distribution network, which is primarily measured by the reliability of electricity supply, is significantly influenced by the shape of the network, the method of grounding the neutral point, the types of faults and disturbances, and the selected relay protection. This paper describes the protection mechanisms of distribution transformers and MV distribution networks with regard to different types of faults and different types of grounding of the neutral points of the feeder transformers.

Abstract: The wind farm construction project is a multi-year complex project, during which all interested parties are exposed to numerous risks. Risk analysis is necessary in order for the investor and the project manager to better predict and avoid potential problems and costs during the project’s lifetime. Through the first part of the work, the theoretical foundations of wind energy, wind speed, and factors that influence wind speed are given. Below are described the basic parts and performances of wind farms, the way they are connected to the grid, as well as the cost structure of the wind farm project, the basic indicators of the economic profitability of the project and incentive measures for renewable energy sources, among which the most important change is the system of stimulating production from the system of guaranteed tariffs to the system of market premiums . In the project assignment, a financial analysis of the wind farm construction project was made according to the future model of stimulating production with a system of premiums. The basic risks in the wind farm construction project are listed, and a model for calculating the profitability of the wind farm was created on a specific example through various simulations in Visual Basic and Microsoft Excel, in which a risk analysis was carried out, as well as an analysis of the project’s sensitivity to changes in key parameters.

Abstract: The paper describes the basic guidelines for the design of TS 10(20)/0, 4 kV, taking into account the specifics related to the design of typical urban, prefab suburban, or pole substations. The basic dispositions and characteristics of MV and LV facilities, the method of protecting the element and the method of grounding the substation are described. The method of sizing equipment in distribution substations is described. On the concrete example of a typical city substation with one dry transformer of 1MVA power, the plant elements were selected and dimensioned. The TS 10(20)/0, 4 kV solution includes an MV plant with two water lines and one transformer field in thering main unit design with SF6 gas. The LV plant is equipped with 12 LV outlets.

Abstract: Distributed production plays an increasingly important role in reducing losses in the network, reducing electricity prices, achieving environmental and economic benefits, reducing investment in production capacity and postponing the upgrade of the transmission and distribution system. This paper deals with the advantages and disadvantages of the growing number of distributed sources. In the introductory part, a broader view of the issues related to the integration of distributed sources is given, and the standard technical conditions that must be met by each power plant when connecting to the distribution network are described. In the third chapter, the effects of connecting distributed sources to the power grid are discussed. An overview of the connection’s influence on voltage conditions, short-circuit currents, power flows, losses and the quality of electricity is given. In the practical part of the work, the situation in the network was analyzed before and after the connection of distributed sources. The analysis includes the impact of the connection of photovoltaic power plants on voltage conditions and losses of working energy in the network for different degrees of penetration of FN power plants into the network.

Abstract: The subject of the thesis is a technological and economic analysis of three ways of lighting control in a hotel. In all larger catering and public facilities, it is in the owner’s interest to have as little electricity consumption as possible, since energy efficiency is one of the basic requirements for a building. It is important that the use of lighting in the exploitation of the facility is as simple as possible. This paper will analyze three ways of lighting control in a hotel: 1. DALI control 2. Control of relays, sensors, timers and programmable relays 3. Classic control For each of the three control methods, the complexity of the design, the complexity and time of execution, the cost of execution and the price of equipment, and the ease of use as well as the possible return on investment with smart control will be analyzed.

Abstract: This thesis consists of a theoretical background of the relay protection schemes in distribution networks that will be activated if the fault occurs. Different methods of the star point grounding in isolated, compensated and low- resistance distribution networks as theirs advantages and shortcomings, considering network topologies and other influences, are described also. Here are shown two relay types : Siemens’s 7SJ62/64 and ABB’s REF615 relay. Both of them are using cos(ϕ)/sin(ϕ) and V0(φ)/I0(φ) measurements due to fault. They are applicable in each of these networks individually. They are used in radial, meshed and looped networks. Both of them can determine fault direction and location. A sensitive, directional ground varmetric element is the classic solution for the ground fault detection in isolated systems. Relay selects automatically the best directional element to use for each particular fault and system condition in low-resistance grounded distribution network. The wattmetric method is the most widely used solution for ground fault detection in compensated systems.

Abstract: The paper deals with the issue of power flow analysis in transmission networks, using the Matpower 6.0 software package, within the Matlab programming environment. It presents the method of preparing input network data, setting the program’s calculation parameters, comparing the Newton-Raphson and Gauss-Seidel algorithms, and analyzing and presenting the calculation results. The calculation procedure for transmission networks of various sizes (16 to 300 buses) is presented, and the influence of capacitor banks on power flows, voltage conditions, and realized power losses is analyzed.

Abstract: The task of this diploma thesis is to carry out an analysis of the economic profitability of building a solar power plant on a selected test example with regard to the current methods of incentives that have been applied in Croatia and the new incentive proposal under the new Law on Renewable Energy Sources and High-Efficiency Cogeneration, and their comparison. In the introductory part, an overview of the development of solar energy in the EU and the Republic of Croatia is given, as well as the directions for the development of this sector in the future. Basic parts, characteristics of operation and production of solar power plants and methods of their connection to the power grid are described. The chronology of state incentives for the FN system of the Republic of Croatia is given, the tariff system for the production of electricity from RES and cogeneration is described, as well as the new law on RES and K. Models of incentives and self-sufficiency are described with examples from other EU countries, as well as the possibilities of obtaining investment incentives. Next, the basic economic parameters used in cost-effectiveness analyzes are described. An Excel model was created for the analysis of annual electricity production according to data on insolation for the Split location, as well as a model for analysis of consumption according to the available consumption data from HEP ODS. The income budget was made in two variants, according to the old and new law, and investment costs and maintenance costs are the same for both cases. The analysis of the economic profitability of building a solar power plant is explained in detail for both cases and accompanied by an example from an excel model. From the analyzes carried out, the conclusion is that the old model of the Law on the Tariff System, which was adopted in 2007, worked in the hands of producers, where it was possible to quickly return the invested capital and make a significant profit, but in the long term, the incentive prices were unrealistic. By changing the law in 2016, following the model of other European countries, a model was created in which there is no direct sale of energy to the grid, but a kind of compensation is carried out, where after settling own consumption, only surpluses are sold to the grid at specially defined market prices. This model is more realistic in the long run, and the analysis showed that it is also profitable for the investor, only with less profit than the previous model. In the future, when we expect a lower price of equipment and an increase in the retail price of electricity, the profitability parameters will be better, and this model will satisfy both manufacturers and suppliers.

Abstract: This thesis examines the capabilities of the PowerWorld 19 simulator in market conditions and its new capabilities compared to previous versions. It describes the general parameters and method for performing a simulation of power exchange between areas, as well as the parameters and method for performing an analysis of the available exchange power, which determines the maximum power transfer (MW) between two parts of the power system without violating any constraints.

Abstract: This paper describes a 3D quasi-static electromagnetic model for calculating the electric field strength of overhead power lines. The phase conductors and protective wires of overhead power lines are approximated by rectilinear thin-wire cylindrical conductor segments, which sufficiently accurately approximate the shape of a catenary. Metal poles of overhead power lines distort the electric field and can significantly reduce its value, so they are also taken into account by being approximated by segments of cylindrical conductors of zero potential. The system of linear equations for calculating the charge density distribution is obtained from the matrix of the eigen and mutual coefficients of all coupled components of the quasi-static electromagnetic model. The distribution of the scalar electric potential and the electric field strength at arbitrarily selected points in the air is calculated by solving a global system of linear equations. In a numerical example, the distribution of the electric field strength in the vicinity of a metal pole of an overhead power line is calculated.

Abstract: The paper deals with the issue of modeling metal oxide surge arresters for the purpose of numerical analysis of switching and atmospheric overvoltages. The IEEE model, the CIGRE model, the simplified IEEE model (Pinceti & Giannettoni) and the Hiszerez model are considered. The simplified IEEE model is implemented in the EMTP software package, for the case of one medium-voltage and one high-voltage surge arrester, and its operation is (numerically) demonstrated for different forms of induced (atmospheric) overvoltage.

Abstract: The goal of this master thesis was to make theoretical analysis of two-phase buck converter with coupled inductor and belonging model in Matlab Simulink. In addition graphical user interface (GUI) for optimization of coupled inductors design was made. In today’s time almost every electronic device requires a power supply device to connect to the electric grid. By modeling converter with coupled inductors, we can reduce phase ripple and with that associated losses also. Benefits of converter with coupled inductors are described in introduction. Buck converter and two-phase buck converter with coupled inductors are described in theoretical part. Waveforms of voltages and currents typical for two phase buck converter with coupled inductors along with the relevant equations are given in the second chapter. Simulation model and simulation results are presented in third chapter. In simulation results is shown how changing the parameters of simulation affects the voltage and current waveforms. In conclusion, results obtained from simulation are analyzed and compared to the results calculated from equations. Graphical user interface (GUI) for optimization of the coupled inductors design along with the code are presented in Appendix A and Appendix B.

Abstract: This paper describes self-consumption systems that provide energy in a switchgear to power relay protection, monitoring, control, signaling, blocking and lighting systems. A calculation was performed for the dimensioning of the AC and DC power supply system equipment using the example of a 110/20(10) kV transformer station. Based on the calculation, transformers for powering domestic consumption and batteries and rectifiers in the 110 V and 48 V auxiliary DC power supply system were selected. Short-circuit current, selectivity control and voltage drop calculations were performed for the selected equipment.

Abstract: In this paper, the TS 110/20(10) kV Sućidar earthing system was modeled based on the available project documentation for the substation and the associated high and medium voltage connecting lines. The earthing system characteristics were calculated and the compliance with the prescribed safety conditions was verified. The earthing system calculation was performed using a special computer program for calculating the earthing system. The reduced current was defined, the method of its calculation was defined, and a specific amount was given for the substation in question based on data on short-circuit currents. The specific soil resistance obtained by measuring using the vertical electrical probing method, with the Schlumberger probe arrangement, was given. The input data of the earthing components were calculated, namely the impedances of the mesh earthing system, the earthing of HV and LV stations, screens and cable earthing systems. The earthing system potential was calculated using the EarthCAD computer program and a 3D representation of the potentials inside and outside the substation was created. By intersecting the 3D representation with planes perpendicular to the potential axis, equipotential lines were obtained. Finally, a verification of the safety conditions was performed.

Abstract: The first part of the paper covers the theoretical foundations of a DC motor with independent excitation. Then, a theoretical analysis of a three-phase thyristor rectifier and its operating modes used in this paper was performed. It is important to emphasize that the output voltage from a three-phase thyristor rectifier is connected to the armature winding of a DC motor through an additional choke. Therefore, the armature voltage is controlled by the control angle of the rectifier, i.e. by decreasing or increasing the control angle, the armature current of the DC motor increases or decreases, which, with constant excitation, is proportional to the electromagnetic torque. A PI controller was used to regulate the armature current (torque). In this paper, the operation of the DC machine was analyzed only in the first quadrant, although the topology of the thyristor bridge used enables a two-quadrant operating mode. A simulation model of the control system in MATLAB - Simulink was used to analyze the electromagnetic torque regulation of a DC motor with independent excitation. Two variants of the rectifier model were used in the simulation of the control system. The simulation model is described with its basic parts and the communication windows of the model used for the simulation are explained. At the end of the work, simulations were performed and analyzed for two successive sudden changes in the torque reference of the DC motor in MATLAB - Simulink, and the influence of the inductance of the additional choke in the armature circuit on the undulation and overshoot in the torque response as regulated quantities was analyzed.

Abstract: The collision of conductors of overhead lines under voltage in most cases results in the creation of sparks which, falling on a flammable substance on the ground, can cause it to ignite. Depending on the vegetation and meteorological conditions, this can later turn into a large-scale fire with extensive property damage. There are few research papers in this area and little available literature describing this phenomenon. In this activity, the problem of collision of conductors with the corresponding mathematical modeling is dealt with. In order to explain this phenomenon, it is necessary to know the flammability properties of certain substances (biomass) on which sparks fall after their formation. In addition, the conditions at the place of collision are important, such as: type of conductor, coordinates of the place where the conductor collided, weather conditions and the amount of current flowing at the point of contact. The way sparks are created, their movement in space and the change in temperature and amount of heat over time are described. Based on this, the critical diameter of the spark is determined from the aspect of igniting the biomass on which it falls. In order to confirm the presented theory, conductor collision experiments were performed in a real low-voltage power network and in the laboratory. The location and circumstances of a live conductor collision are random variables, so the number and size (diameter) of sparks (particles) are also random variables. Accordingly, it is important to determine which probability density function best describes the diameter distribution. Based on the critical diameter and the function The probability distribution of the diameter determines the probability of biomass ignition on the ground. From the aspect of protecting an element of the power grid from overload and short circuit, in addition to the existing criteria for selecting the type, and then the setting of the protective device, a new, additional one is introduced, which refers to protection against biomass ignition. on the ground due to the collision of conductors. The scientific contribution of this dissertation is reflected in the statistical approach to defining the number and diameter of electric sparks, and thus the probability of biomass ignition on the ground and the occurrence of a fire. An original algorithm was created for determining the critical spark diameter from the aspect of biomass ignition (critical temperature and the required amount of heat). A new criterion has been formed for the selection of time-current characteristics of protective devices in the power grid for the purpose of fire protection in the event of conductor collision. The results of this doctoral dissertation have practical applications, as they can provide answers to questions such as the probability of a fire occurring due to conductor collision. Based on this, the owner of the line can proceed with the design of its protection.

Abstract: This paper describes an algorithm that, by combining heuristic methods and a genetic algorithm, enables optimal reconfiguration of medium-voltage distribution networks while satisfying all operating constraints and maintaining the radial structure. The proposed algorithm introduces a number of improvements compared to previous similar achievements, which enables it to be applied to real distribution networks. With the algorithm, it is possible to achieve two goal functions, minimization of total losses of active power or equalization of load in the network. The algorithm was tested on standard test networks where it was shown that the complexity of the network does not affect the efficiency of the algorithm. In addition to standard test networks, the algorithm was also tested on a real medium-voltage distribution network, and the calculation results show the quality and accuracy of the obtained results. The algorithm leaves enough room for the introduction of further modifications in order to achieve better efficiency.

Abstract: This paper describes the general problems of the integration of renewable energy sources into the power system, with an emphasis on the distribution network, both its planning and the influence of distributed sources on its operation. The paper describes the methods of determining the optimal power and connection point of the distributed source in the distribution network based on the sensitivity factors of the change in losses in the network, the method of the golden ratio, the method based on the assessment of the change in power losses in the network based on incidence matrices. The described methods were implemented in the form of a software package and were tested on radial distribution networks. The paper presents the obtained results, which include the optimal locations and power of distributed sources, and provides a comparison of the obtained results for the different methods described in the paper.

Abstract: This thesis deals with the various methods for lightning strikes monitoring and identification, with special emphasis on the LINET network operation. Lightning detection with TOA method is described, along with the method of separating CG from IC lightning strikes. Possibility of using lightning products of LINET network in creating lightning density and lightning hazard maps is explored, along with the possibility of identifying lightning flash- cells, their tracking and nowcasting (i.e. forecasting their short-term position).

Abstract: This thesis analyses different possible implementations of the numerical relay protection functions for the generator loss of excitation protection. Two different implementations of the generator loss of excitation protection are described: (1) 7UM6x relay from Siemens and REG650 relay from ABB. Setting of the function’s various parameters is shown for a concrete generator data.

Abstract: Electricity is treated as a commodity today. The quality of electricity, at all voltage levels, is strictly defined by international standards, the most important of which for our area is the European standard EN 50160. This standard should be briefly described in the diploma thesis and an analysis of the quality of electricity in the area of ​​TS Dugopolje should be carried out based on the measurement of registered data. 110/10 kV/kV. It is also necessary to conduct an analysis of electricity consumption for four characteristic weeks.

Abstract: The paper should provide a historical overview of relay protection with a special emphasis on current numerical relays. Also, the ABB numerical relay, type REF615, should be described in detail. Furthermore, the candidate should state the characteristics of the Omicron CMC-256/6 relay testing instrument as well as the PGX30 relay testing measuring system from CMC Protection. Using the mentioned systems, measurements should be carried out on a specific example to verify the correctness of the relay, compare the measurement results obtained with different instruments and create appropriate test protocols.

Abstract: The first part of the paper deals with the theoretical foundations of a DC motor with independent excitation and speed control by changing the armature voltage to the rated speed. Then, a theoretical analysis of a single-phase thyristor rectifier, its operating modes, and the control and output characteristics of the rectifier was performed. It is important to emphasize that the output voltage from a single-phase thyristor rectifier is connected to the armature winding of a DC motor. This armature voltage is controlled by the control angle of the rectifier, i.e. by reducing or increasing the control angle, the speed of the DC motor is increased or decreased at a constant mechanical load. The ratio of the control angle to the armature voltage (speed) is the basis on which speed control is based. When the mechanical load of the motor is variable and there is a need for the speed to follow the reference speed and to maintain system stability and reduce unwanted system oscillations, then there is a need for speed control. In this paper, a cascade control system for two-quadrature operation with PI controllers is used for speed control. To analyze the speed control of a DC motor with independent excitation, a simulation model of the control system in MATLAB - Simulink was used. The simulation model is described with its basic parts and the communication windows of the model used for simulation are explained. At the end of the work, simulations of the characteristic operating modes of the DC motor were performed in MATLAB - Simulink and the effects of selected system parameters on the behavior of system variables were analyzed.

Abstract: The purpose of this work was developing of a special magnetic sensor which can measure magnetic fields generated by lightning impulse currents. High facilities have a high risk of being hit by lightning, and thus, they are threatened by induced magnetic field. Example of such facility is wind turbine nacelle. Time- varying magnetic fields, generated by lightning currents, induce high voltages in close metallic structures of facilities. These voltages can harm sensitive elements, such as electronic circuits and control systems. The first step in preparing of protection measures is measurement and estimation of magnetic field within such structures in case of lightning strike. Estimation of magnetic field is done by numerical calculation with FEM software COMSOL Multiphysics. With certain assumptions and different approaches, the maximum estimated value of the magnetic field inside of a wind turbine nacelle was around 50 kA/m. With frequency, specified by IEC standard, the required parameters for magnetic sensor were defined. With known parameters of the magnetic field, proper magnetic sensor can be chosen or developed. Different magnetic sensor types were investigated, and the inductive sensor meets best the requirements. Advantage of inductive sensors is their simplicity of manufacturing, low cost and their measuring field range. This type of sensor shows a linear characteristic. The needed integrator for obtaining magnetic field strength and shape requires a corresponding measuring circuit. This circuit can be affected by magnetic fields induced in wind turbines, and the problem can be solved with proper EMC protection of that circuit. Various simple inductive loop sensors were built and tested. The different abilities of the inductive sensors were discussed, and some fine conclusions were obtained. The sensors shown great measuring accuracy. It was proved that they can measure the magnetic field regardless on the direction or amplitude, so it makes them perfect for measuring of the transient magnetic field within any construction struck by lightning.

Abstract: The paper presents the analysis and numerical calculation of the dynamic stability of a hydrogenerator under conditions of disturbances in the incident transmission network. The occurrences of three-pole, two-pole and single-pole short circuits and sudden load loss are considered. In the event of short circuits, the influence of automatic reconnection (APU) on the dynamic stability of the generator is analyzed, as well as the duration of the fault itself. The hydrogenerator is modeled together with the turbine regulation and excitation regulation systems (including PSS and OEL and UEL elements). The model is implemented using the Matlab Simulink environment. In addition, the paper provides theoretical foundations for modeling a complete hydropower plant (hydraulic installation, turbine, turbine regulator) with the possibility of simplification and neglect within the complete model. Different designs of generator excitation systems are also described and then the so-called standard IEEE models of generator excitation systems are presented.

Abstract: The paper presents the procedure for parameterizing a numerical relay device type 7SJ8x from Siemens using the DIGSI 5 software package on the example of protecting a cable line in a distribution network that is grounded via a small active resistor. The paper presents the selection of current and voltage transformers for connecting the relay device, the calculation of the settings of relevant protection functions (low-adjustable and high-adjustable overcurrent protection against phase-to-phase short circuits, sensitive directional homopolar overcurrent protection, thermal protection, etc.), and the configuration of the relay device (opening a project, adding a relay device, defining the settings of protection functions, etc.).

Abstract: This thesis provides a detailed steps for the configuration of the protection settings, using the DIGSI 4 software package by Siemens, for the numerical relay protection of autotransformer (with a stabilization tertiary winding). The relay type 7UT6x is employed for that purpose. Following protection functions of the said relay have been employed for the autotransformer protection: differential protection, REF protection, overcurrent protection, thermal protection and overexcitation protection. Parameters of the current and voltage transducers for the concrete application were selected as well. All necessary parameters of the protected object, current and voltage transducers, as well as protection function settings, were configured on the relay, in the offline mode, using the DIGSI 4 software package by Siemens.

Abstract: Using the Siemens DIGSI software package, all the most important steps that need to be taken to set up the relay protection system of a typical single-phase high-voltage transmission line in a transmission network are shown in detail. A Siemens 7SA6x numerical relay device was used. The following protection functions were calculated and selected: distance protection (quadrilateral tripping characteristic with three stages of operation), distance protection communication scheme (PUTT Z1B), directional homopolar overcurrent protection (ANSI 67), ordinary overcurrent protection (ANSI 50/51), power swing blocking. The parameters of the associated current and voltage measuring transformers were also selected. All necessary parameters were set on the aforementioned relay device, in offline mode, using the Siemens DIGSI software package.

Abstract: The paper describes the basic properties of electric power in an alternating current system. The main consumers of reactive power are listed, especially transformers in distribution networks and asynchronous motors used in industry. Furthermore, various types of compensating devices, their technical and economic advantages are listed, and a special part of the work refers to the most used capacitor batteries. Finally, detailed calculations of typical compensation claims are added.

Abstract: Through the first part of the paper, the theoretical foundations of reactive power are given and the basic problems of integrating capacitor batteries into the system are highlighted. The advantages and disadvantages of using capacitor batteries and the techno-economic benefits of compensation are explained. Before the practical part, an overview of the advantages and problems of using genetic algorithms is given. After the aforementioned theoretical considerations, the parameterization calculation of the genetic algorithm was performed, where various influences of the parameters on the quality of the solution and the speed of convergence can be seen. Then, the calculation of the installation of capacitor batteries in the network was performed using a genetic algorithm using a standard example of a network with 69 buses, and the results of power flows and voltage conditions before and after the installation of capacitor batteries in the network were compared.

Abstract: Calculation of power flows is one of the basic calculations used in stationary plant analysis and planning of the power system (EES). Unlike transmission networks, distribution networks in regular operation are fed radially, which enables a simpler and faster calculation of power flows. The goal of this paper is to create a computer program for calculating power flows in radial distribution networks based on the backward-forward algorithm. It is also necessary to explain and computer-implement algorithms for topological sorting and detection of loops in networks. The developed computer program will be applied to typical distribution networks and the results will be compared with commercially available programs for this type of analysis.

Abstract: The paper describes the basic parts, characteristics of operation and production of solar power plants and the method of connecting them to the power grid. The basic structure of the costs of building a solar power plant is stated, and a model for analyzing the economic profitability of the construction is created. The basic economic parameters used in the analysis of the profitability of the project are defined. On the selected test example (location Split and Zagreb), based on the created model, an analysis of the economic profitability of the construction was carried out with regard to the currently valid purchase prices of electricity and currently valid equipment costs.

Abstract: By integrating electrical energy storage equipment into consumer facilities, greater flexibility is achieved in terms of powering the consumer, and it enables the consumer to control the download of electricity from the power system in accordance with current market prices. In addition, positive effects are also achieved from the aspect of the electric power system, since such consumers can participate in the provision of auxiliary services in the system if they receive an incentive for it. The paper explains the technology and ways of storing electricity, and the storage costs of individual technologies are listed. In addition, a computer program was developed that enables the calculation of the optimal way of powering an industrial consumer that has devices for the production (diesel aggregate or photovoltaic power plant) and storage (batteries) of electricity within its facility. Based on the known technical data on consumer equipment, that is, data on electricity consumption and the prices of the appropriate tariff model for a certain period, the profitability of different consumer power supply strategies was examined.

Abstract: This doctoral thesis describes an originally developed electromagnetic model for calculating the distribution of ground fault current in power plants, which is based on the application of the finite element technique to the integral formulation of the problem. The components of the electromagnetic model can be located in homogeneous soil or in air. The damping and phase rotation of the electromagnetic wave are approximately taken into account using the damping-phase factor. The developed electromagnetic model can take into account the complete electromagnetic coupling between the components of the electromagnetic model. All mutually electromagnetically coupled components of the electromagnetic model form one finite element. The components of the electromagnetic model are: the earthing switch of the considered transformer station, the earthing switches of neighboring transformer stations, power transformers, metal poles and earthing switches of overhead power lines, protective ropes and phase conductors of overhead power lines, metal screens and phase conductors of underground power cables, earthing conductors laid above underground cable lines and other conductive parts. Based on the known ground fault currents in the neighboring transformer stations, from which the transformer station affected by the ground fault is powered, one or more three-phase voltage sources are formed in each of the neighboring transformer stations. In this way, the power flows in the power system are taken into account. A particular part of the power system can be replaced by an impedance, which forms a separate finite element. Based on the developed theoretical basis, the computer program EMFCD has been developed, which is primarily intended for calculating the distribution of ground fault currents. However, this computer program can also be used for advanced analysis of current and voltage conditions on overhead and cable power lines.

Abstract: The paper presents the application of IEC 60071 in the analysis of insulation coordination of high-voltage switchgear and substations. Special emphasis is given to the assessment of expected atmospheric overvoltages as a consequence of the occurrence of close flashovers on incident transmission lines.

Abstract: This paper describes the basic parts, operation and production characteristics of wind power plants and their connection to the power grid. The basic structure of the costs of the construction of wind farms is stated, and a model for the analysis of the economic profitability of the construction of a wind farm is developed. The basic economic parameters used in the analysis of the profitability of the project are defined. On the chosen test example of the wind power plant, an analysis of the economic profitability of the construction was carried out with regard to the currently valid purchase prices of electricity and the current level of costs. A sensitivity analysis and a risk analysis (based on Monte Carlo simulation) were performed with regard to the selected input parameters of the model.

Abstract: The paper describes the issues of designing a relay (electrical) protection system for synchronous generators of different nominal powers, with an emphasis on generators with salient poles. The issues of selecting protection functions are analyzed with respect to the method of connecting the generator to the grid (distribution grid, transmission grid, generator busbars, block connection), the method of grounding the generator voltage level (and the method of grounding the incident grid), the generator nominal power, the design of the generator excitation system, the design of the stator winding (number of parallel branches, third harmonic level), etc. Different design variants are compared and analyzed: (i) differential protection of the generator-transformer block (with or without a tap, generator switch), (ii) ground-fault protection of the stator winding (overcurrent, overvoltage, based on the third harmonic, with voltage injection into the star point). The possibilities offered by the numerical relay device type REG650 from ABB are presented, with respect to the design of the relay protection system for synchronous generators.

Abstract: Renewable sources increase the self-sustainability of the electric power system in the event of a possible energy crisis in the production of electricity, which today is dependent on the supply of coal, gas and oil. In addition to the mentioned problems, when connecting distributed sources to the distributed network, there is a significant change in the technical properties of the distribution network and the appearance of problems that were not characteristic of these voltage levels until then. One of such problems is the occurrence of high voltages and overloads in distribution networks with high shares of distributed sources. In such conditions, the current methods of leading and managing the distribution network are no longer sufficient. In this paper, the impact of the connection of wind power plants and photovoltaic power plants on the operating conditions in the distribution network was investigated. The paper also proposed a model for optimal coordination of the production of working and idle power from distributed sources, which ensures normal operating conditions even with high shares of distributed sources in relation to local consumption.

Abstract: Power system simulation using computers is becoming more and more important in design, management and education. Various calculations are required for this, such as power flows, state estimation, random event analyses, security analyses, transmission stability analyses, etc. In this paper, the theoretical bases for the calculation of alternating power flows in electric power networks are defined. Algorithms based on the Gauss-Seidel method, the Newton-Raphson method, and the algorithm of fast separated power flows, or their combination, were specially developed. Within the Matlab software package, the aforementioned algorithms for the calculation of alternating power flows are implemented. For given power networks, the calculation of alternating power flows was performed using developed algorithms. On the basis of the conducted analyses, the advantages and disadvantages of each method were indicated.

Abstract: In the introduction, the need for optimization of reactive power is described in a few sentences and a description of the work is given. In the second chapter, what is reactive power is briefly explained and the hierarchical levels of reactive power management and the economic aspects of reactive power management are briefly described. In the third chapter, a general description of devices used for voltage regulation and optimization of reactive power in the network is given. The fourth chapter concerns methods of optimal engagement of reactive power. The mathematical formulation of the classical approach to reactive power optimization is given, as well as the general model of reactive power optimization using evolutionary algorithms. The methods of optimal engagement of reactive power are briefly described. The fifth chapter describes the particle swarm method and the application of the particle swarm method for reactive power optimization. The sixth chapter presents the practical part. The network is described, which is taken as an example of reactive power optimization using the particle swarm method, and the basic technical characteristics of the network and devices used for reactive power optimization are given. The second part of the sixth chapter consists of various calculation variants characterized by different input settings of the particle swarm method.

Abstract: In this doctoral thesis, an improved quasi-static electromagnetic model for calculating the low-frequency electromagnetic field of power lines and facilities has been developed. The basis of the developed model is the application of the finite element technique to the integral formulation of the problem in the frequency domain. A thin-wire approximation of cylindrical conductor segments is used. To describe the passive conductive parts of electrical facilities and overhead line poles, spatial 2D subparametric finite elements with an arbitrary number of nodes have been developed to describe the distribution of the areal charge density per individual finite element. In the numerical model, it is assumed that the cylindrical segments of active and passive conductors have a constant line charge density, which is mathematically located in the conductor axis. The singularity problem that occurs with double integration by spatial 2D finite elements has been solved by developing an advanced algorithm for double numerical integration based on Gaussian numerical integration. An algorithm for segmenting conductors and overhead line poles based on basic input data on their geometry has also been developed. The phase conductors and protective wires of overhead power lines are approximated by a set of straight cylindrical segments, which sufficiently accurately approximate the shape of a catenary. The influence of passive conductive parts of power lines and facilities on the distribution of electric field strength and magnetic induction is also taken into account. The influence of passive conductive parts on the distribution of magnetic induction is calculated using a set of real and equivalent current contours. The accuracy of the developed quasi-static electromagnetic model for calculating the low-frequency electromagnetic field of power lines and facilities is confirmed by comparing the calculation results with the results obtained using other software packages, with analytical solutions available in the literature, and with measurement results.

Abstract: This paper provides an insight into power flows in a system with included variable energy sources, in this case wind farms. In the first chapter, the basic facts about wind, how it is created, how much wind energy is and how it is calculated, are presented, then the wind distribution density functions are given. Basic things about wind turbines, their types and parts of individual wind turbines are explained. It is shown how the wind affects the production of wind turbines and how wind farms affect EES. In the second chapter, the importance of power flows in the EES is presented and the main principles of calculating power flows using deterministic and probabilistic methods (point estimate method, method of cumulants, Monte Carlo method) are explained. In the third chapter, an insight into the probabilistic Monte Carlo method is given. The methods of generating the input variables of the method are given and the method of calculation is explained. Chapter number four is the practical part of this work, where the calculation of power flows using the Monte Carlo method for the case without wind farms in the system, as well as cases with connected wind farms for different levels of correlation, was made on the 24-IEE bus model.

Abstract: This thesis consists of seven chapters, which will be briefly described below. The first chapter is an introduction, through which a brief description of working with goals is given. Through the second chapter of the paper, the theoretical foundations of wind energy are given and the basic problems of wind energy integration into the system, its utilization and wind speed distribution described by Weibull and Rayleigh probability distributions are highlighted. In the third part, modern versions of wind turbines as well as their parts (tower, rotor, gearbox, brakes, generator) and power regulation of wind turbines are described. In the fourth chapter, an overview of the connection of the wind power plant to the power grid is given, as well as the topology of the internal MV network, a medium-voltage plant is also described with examples of distribution cabinets and a presentation of the switching apparatus used in the MV plant. Along with the medium-voltage plant, a description of the types of medium-voltage cables used for connection and their characteristics is given. The fifth chapter gives examples and a description of three different methods of calculating annual electricity losses. energy (annual simulation of power flows on an hourly basis, discretization of the production duration curve, approximate calculation). The sixth chapter refers to a brief description of the data of the wind turbine that was taken as an example in this thesis, a detailed description of two variants of the internal VE network (spatial representation of wind farms and cable network outlets) that were considered in the analysis. After the aforementioned theoretical considerations, a computer simulation of the calculation of annual electricity losses was performed. of energy and comparison of used methods, calculation of investment costs, costs of electricity losses. energy and selecting the most favorable variant using the cost difference method.

Abstract: The paper explores the theoretical background of highly sophisticated mathematical models of lightning strike development in freestanding structures: these are the so-called leader inception and leader progression models. Special attention is paid to the following models: Eriksson’s model, Rizk’s model, Dellera and Garbagnatija’s model, and Becerra and Cooraya’s model. A comparison of the aforementioned mathematical models is made and detailed comments are given on the theoretical assumptions on which the models are based.

Abstract: The paper deals with the issue of choosing external insulation (for transmission lines and external switchgear) under conditions of significant snow and/or ice impact. The parameters of snow and ice that influence the occurrence of jumps on the external insulation of HV transmission lines and apparatus in switchgear were analyzed. Methods of testing insulation under the influence of snow and ice in high-voltage test laboratories equipped with special ice chambers are presented. Recommendations for methods of testing and designing (execution) of external insulation are presented, as well as the selection of tolerable external insulation voltages in conditions of increased influence of snow and ice.

Abstract: The paper describes the issue of protecting dual-system high-voltage transmission lines using distance protection. The analysis of the calculation of the measured impedance of the distance protection for different types of short circuits is presented and its visualization in the R, X coordinate system. The criteria for selecting the distance protection settings (1st and 2nd stage) of dual-system overhead lines where electromagnetic coupling is present in the neutral system are also presented in detail. The criteria consider three different possible switching states of the dual-system transmission line and analyze the error of the measured impedance with respect to the switching state and the initial range setting, especially for the 1st stage and especially for the 2nd stage of distance protection. The analysis of the distance protection settings with the verification of selectivity and sensitivity is presented on a specific example of a dual-system line in a transmission network.

Abstract: The paper describes the problem of determining (estimation) the number of direct lightning strikes in high-voltage power lines, based on the application of electrogeometric models (EGM) of lightning strike development. The problem of determining the number of lightning strikes in the phase conductor in power lines with one or two protective wires (the so-called SFR value) and the problem of determining the resulting number of flashovers due to direct lightning strikes in the phase conductor (the so-called SFFOR value) were also analyzed. Based on the appropriate mathematical models, computer programs were developed in the MATLAB programming environment and a comparative analysis of several different EGM models was made (Wagner, Young, Love, Armstrong & Whitehead, Eriksson, etc.).

Abstract: This doctoral dissertation proposes an original method for selecting and optimizing the basic parameters of the LCL filter of a three-phase PWM inverter. The developed method is in accordance with IEC and IEEE standards on permissible current distortion and takes into account the influence of nonlinearity, especially dead time, on the characteristics of the inverter. The analysis of the influence of nonlinearity was performed at the simulation level for the case of an unregulated three-phase PWM inverter with an LCL filter. The model verification was carried out based on the comparison of simulation and experimental results. Within the framework of the developed method for selecting and optimizing the basic parameters of the LCL filter, a new criterion function based on reducing the inverter losses was defined. The validity of the developed method was verified on the example of selecting the parameters of the LCL filter of a commercial indirect frequency converter. As part of the research conducted, measurements of the total losses of the filter chokes were performed, which also include the losses of higher harmonics. Based on the results of the aforementioned measurements, an improvement of the choke model was proposed that takes into account the losses of higher harmonics. Finally, measurements of total system losses were performed and a procedure was proposed to determine the optimal carrier signal frequency for the analyzed system.

Abstract: Modeling of hydrological systems is generally based on time series, and instead of previously used linear statistical models, artificial neural networks are being used more and more recently. In the case of models for forecasting hydrological inflow, a review of the available literature revealed the problem of a delay in the model’s response after an actual event, which significantly reduces the usefulness of the model’s prediction. The same problem was confirmed in the model formed by classical methods for the Cetina river basin. The problem of timely forecasting in this dissertation is successfully solved by introducing the variable frequency of forecasted precipitation and by adjusting the calculation step. Forecasting accuracy is improved by forming an optimized adaptive neural model (OANM) based on dividing the model into specialized sub-models, which represent specially trained networks for forecasting at certain times of the year. Each submodel was formed according to the principles of a systematic approach to the formation of neural models for hydrological predictions. This means that the optimal input variables, the number of neurons of the hidden layer, the algorithm for training the network and the objective function were determined through specially formed experiments, and a set of optimal measures for evaluating the model was also determined. A static feedforward neural network, a multi-layer perceptron, was used to form all models, due to its proven property of being able to approximate a non-linear function. The MATLAB program was used for all research, as well as the final formation of OANM, and the data were processed in Microsoft Excel in addition to Matlab. The simulation results confirm the success of the proposed method in solving the problem of timely and reliable forecasting of hydrological inflow, which means that the proposed method successfully eliminates the delay of model prediction.

Abstract: In this doctoral thesis, a transient electromagnetic model for the analysis of a grounding system in a horizontally stacked multilayer medium has been developed. The basis of the developed model is a harmonic electromagnetic model based on the application of the finite element technique to the integral formulation of the problem in the frequency domain, with a thin-wire approximation of the conductor segments of the grounding system. Each conductor is divided into segments, and all electromagnetically coupled segments form one finite element. The longitudinal currents of the conductor segments change linearly along the segments, and the segments discharge the transverse current uniformly into the surrounding medium. The self and mutual impedances of the conductor segments have been calculated using the mean potential method. It is possible to include bare cylindrical and rectangular conductors of the grounding system and metal screens of single-core and three-core power cables in the calculation. By using the damping-phase factor, the time-consuming and complex solution of Sommerfeld integrals has been avoided, and despite this, very high accuracy has been achieved. For the transition between the time and frequency domains, a highly accurate, fast and robust continuous numerical Fourier transform was originally developed, which is characterized by arbitrary and mutually independent sampling in the time and frequency domains. Thanks to this fact, it is possible to take into account the soil ionization very accurately, despite the fact that the main calculation is carried out in the frequency domain. The accuracy of the developed transient electromagnetic model for the analysis of the grounding system in a horizontally arranged multilayer medium is confirmed by comparing the calculation results with experimental and numerical results available in the literature.

Abstract: In this doctoral dissertation, a new dynamic model of an asynchronous machine with iron losses included is proposed. Within the proposed model, iron losses are represented by an equivalent resistance whose value depends on the stator frequency and the magnetic flux in the air gap. The proposed model was first applied at the simulation level to analyze the operation of an unregulated self-excited asynchronous generator. The validity of the simulation model was confirmed based on comparison with experimental results. The proposed model was then used to develop a new vector control system. Within the developed system, the calculation of the equivalent resistance of iron losses and inter-inductance is performed in real time using the corresponding characteristics, which were previously determined as part of the no-load test. Testing of the developed vector control system was performed at the simulation and experimental levels. After the validity of the proposed approach was confirmed, two new algorithms were developed to optimize the efficiency of the control system. The algorithms were tested at both simulation and experimental levels and a significant increase in system efficiency was found due to the application of the algorithms. In addition, the calculated amount of total control system losses was corrected for the estimated losses of the routers in the system.

Abstract: Transport in the modern globalized world is one of the important factors that significantly affects the functioning and development of industry. The introduction of shipping containers in transport reduced the waiting time of ships in the port, and the modernization of port terminals paved the way for automation and the application of industrial computers in loading and unloading cargo. Crane systems are very flexible, due to the poorly damped poles introduced by the cargo. The flexibility of the cargo introduces the sensitivity of the system to external influences such as wind. The consequence of poorly damped poles is oscillation, which occurs during cargo transfer. Cargo oscillation negatively affects the speed of cargo transfer and safety in the vicinity of the crane. This paper presents a predictive controller, which ensures rapid transfer of cargo to the target location while preventing cargo oscillation. An appropriate mathematical model of the crane is proposed, which takes into account the dynamics of changes in the height of the cargo. A cargo with a fixed and variable center of mass is considered. A cargo with a variable center of mass introduces additional oscillations in the crane system, which can lead to instability of the control system. The proposed predictive controller was tested and compared with a classical crane control system through simulation and experimental tests on a laboratory model.

Abstract: In this paper, the calculation of transients on a multiwire line is performed using the finite element method, including the frequency dependence of the parameters of the multiwire line. The multiwire line has been a subject of interest for a long time. Therefore, a review of the most famous methods for calculating transients on a multiwire line is an integral part of the dissertation. High-quality input data, i.e. frequency-dependent parameters of the multiwire line, are necessary for testing numerical models. Therefore, the paper also includes some methods for calculating frequency-dependent parameters of a multiwire line, including frequency scanning, which can also be used for frequency analysis of more complex systems, e.g. parts of electrical networks. Numerical modeling of electromagnetic transients on a multiwire line with frequency-independent parameters using the finite element method in the time domain is a kind of introduction to the main part of the dissertation. This model is the starting point from which a new numerical model of a multiwire line with frequency-dependent parameters was obtained. The derivation of a new mathematical finite element model of a multiwire transmission line, including the frequency dependence of the parameters, is the central part of the dissertation. Frequency dependence is achieved by including the convolution calculation in the system of finite element equations of a multiwire line. Based on the presented model, a computer program for the calculation of electromagnetic transients on a multiwire line in the MATLAB programming environment was developed. Finally, selected numerical examples were solved using the finite element method with frequency-dependent parameters. The correctness of the presented numerical model was proven by comparison with solutions from the literature and by using other computer packages for transient analysis. The original scientific contribution of this work is the development of a new numerical model for the calculation of electromagnetic transients on a multiwire transmission line based on the finite element method in the time domain with frequency-dependent parameters included.

Abstract: The paper describes the issue of protecting high-voltage transmission lines using distance protection. An analysis of the calculation of the measured impedance of distance protection is presented for different types of short circuits, as well as its visualization and interaction with the MHO and polygonal type operating characteristics. The influence of the transition resistance at the fault location on the measured impedance of distance protection is also analyzed. Finally, on the example of a specific section of the 110 kV transmission network, a method of calculating the settings of the distance protection parameters of a single transmission line is presented, using numerical relay devices type 7SA6x from Siemens.

Abstract: The dissertation describes in detail the development of the electromagnetic and thermal model of the human brain. The electromagnetic model based on integral equations was derived using the equivalence theorem with the application of boundary conditions for the case of a dielectric body of arbitrary shape with losses included. The thermal model of the brain is based on the form of the Pennes equation of heat transfer in biological tissue extended by an additional term representing the absorbed electromagnetic energy density. In addition to detailed guidelines for calculating various surface integrals that occur in the electromagnetic model, an adapted analytical-numerical technique for singularity extraction is presented, useful for correcting instabilities that occur when using a purely numerical approach. The developed electromagnetic-thermal model was applied to internal dosimetry of the human brain to determine the absorbed electromagnetic energy and the consequent increase in temperature due to exposure to an incident plane high-frequency electromagnetic wave. Furthermore, the developed model was also applied to rigorous modeling of the transcranial magnetic stimulation technique, where, by including radiation effects, a more exact physical description of the problem is obtained compared to existing models. Finally, the sensitivity of the results to changes in various electrical and thermal tissue parameters used in the model was examined, and a comparison of internal brain dosimetry in an adult and a ten- and five-year-old child was provided, taking into account age-dependent tissue parameters.

Abstract: The paper presents the issues of implementing a relay protection system for induction motors connected at a voltage level of 0.4 kV. The implementation of protection against overload and asymmetrical load, as well as protection against phase-to-ground short circuits of an induction motor, is analyzed, taking into account various possible ways of starting induction motors. The paper also presents the selection and parameterization of a relay protection system for a specific induction motor, based on the use of Compact NSX circuit breakers from Schneider Electric.

Abstract: The paper presents the issues of designing resistive and capacitive voltage dividers for measuring high (AC, DC and surge) test voltages. The paper also theoretically discusses the issues of obtaining the appropriate transfer function/characteristics of high-voltage voltage dividers, and using the EMTP software package, one specific high-voltage voltage divider was simulated and its transfer characteristic was determined.

Abstract: The paper presents the issue of selecting the grounding method for a typical wind farm’s medium-voltage cable network, considering the magnitude of the short-circuit current to ground and the amount of expected internal and temporary overvoltages. The methods of low-resistance grounding and grounding using a Petersen choke, as well as the isolated network mode, are considered. The issue of implementing a relay protection system for a typical wind farm’s medium-voltage network is also considered, from the aspect of the selected grounding method, with special emphasis on protection against short circuits to ground.

Abstract: The paper deals in detail with the issue of selecting the optimal relay protection system for the stator winding of a synchronous generator against short circuits to the ground, depending on the method of connecting the generator to the network and the method of its grounding. Different methods of implementing the so-called 95% ground fault protection and the so-called 100% ground fault protection of the generator stator are considered. Attention is also paid to the method of mutual coordination of various protection functions. The selection and setting of protection against short circuits to the ground is shown using the example of a specific generator.

Abstract: Due to the strong development of wind power and lack of investment in the development and revitalization of the transmission network, there is a need for a methodology that will enable the identification of maximum wind power plant integration capabilities into existing transmission network without the need for additional investment in network development, and without significant disruption of relations in the electricity market. The methodology proposed in this thesis is based on a one-year simulation of power system operation with wind power plants on an hourly time basis. Simulation represents a complex optimization problem that is solved by iteratively solving a series of simple subproblems. In the first subproblem, the order of conventional power plants commitment is determined as well as power distribution on deployed units in the system, based on incremental costs of their production, for each hour of the studied time frame. In the second subproblem, the boundary limit on individual wind power plant installed capacity scheduled for connection to a pre-defined network node is determined, taking into account the limitations of the transmission system under normal and N-1 operating conditions, while considering given ( maximum planned) capacities of wind power plants on each location. In order to eliminate a large number of redundant linear constraints in the second-level subproblem enabling its solution, a reduction scheme based on a quick convex hull algorithm is implemented. In addition, since simultaneous wind speed (wind power) data at different locations are often unavailable or not sufficiently long, methods based on vector autoregression and Markov chains that can generate realistic simultaneous time series of wind speed (wind power) data are developed.

Abstract: The paper analyzes the criteria based on which the value of the effective resistor for grounding the distribution network is determined. The criteria relate to meeting the conditions of the earth fault current limit, internal overvoltages and dangerous voltages resulting from the permissible single-pole short-circuit currents and the method of grounding of the TS 10(20/0, 4 kV. The following criteria were considered, among others: Edith Clark criterion, Clem criterion, Petersen criterion, High-impedance grounding criterion, Low-impedance grounding criterion, Criteria according to the HD637S1 standard.

Abstract: The paper deals with the implementation of stabilized (longitudinal) differential protection of autotransformers with a tertiary winding, with an emphasis on its three-point protection. Various possible variants of installing current transformers on the tertiary winding (taking into account whether the tertiary is intended for loading or a stabilization winding) and their consequences on the implementation of differential protection of the three-point autotransformer were considered. An example of protecting an autotransformer with a stabilizing tertiary winding, three-point differential protection, using a numerical relay device type RET670 from ABB is shown.

Abstract: The paper analyzes the problem of protection of a small active resistor for grounding the distribution network. The mentioned small active resistor is installed in the constellation of the associated winding of the power transformer in the feeder substation (one resistor per transformer or one resistor per substation). The application of the following protections was analyzed: (i) protection against bridging of a small active resistor, (ii) protection of an active resistor and back-up protection against short circuits with the ground in the distribution network and (iii) protection against high-resistance faults. An overview of the selection of basic technical data of current transformers for the connection of the mentioned protections (especially those that are installed in the constellation of windings of the energy transformer) is given.

Abstract: The paper presents the theoretical basis of the so-called of the Liew-Mar model for the analysis of overvoltage conditions on an overhead line (power line) that occur as a result of a close (indirect) lightning strike. It is an analytical model that, among other things, takes into account the influence of the steepness of the lightning current front on the realized water overvoltages. On the basis of the aforementioned theoretical basis, a corresponding computer program was developed in the work, which then analyzed the influence of close lightning strikes on the occurrence of overvoltage conditions in typical MV transmission lines while varying characteristic values ​​such as the height of the conductor above the ground, the distance of the lightning strike from the overhead line, the height of clouds above the ground , the speed of the lightning strike, the steepness of the lightning current front. In addition, the results obtained by the mentioned model were compared with the results of the calculations carried out using the so-called Chowdhuri-Gross model.

Abstract: The paper presents an analysis of methods and systems for detecting and locating lightning strikes, with an emphasis on LINET and NLDN networks. The functioning of sensors used by the aforementioned networks for detecting lightning strikes is described, as well as the method of distinguishing between cloud-to-cloud and ground-to-ground strikes. A brief comparison of the aforementioned systems/networks for detecting and monitoring lightning strikes is made, as well as their historical development, with a special emphasis on the NLDN network. The paper also provides a brief theoretical background to the statistical expression of lightning parameters (amplitude, front duration, crest duration, charge, etc.).

Abstract: The paper analyzes the problem of modeling lightning strike current for the purpose of determining the radiated electromagnetic field in the environment of a lightning strike to the ground. The aforementioned analysis is otherwise used as part of a broader model for predicting the impact of an indirect lightning strike to the ground in the vicinity of MV and LV overhead lines. The paper describes the existing so-called engineering models of lightning strike current, and their mutual comparison is made. The influence of the input parameters of lightning strike current (e.g. strike speed, etc.) on the behavior of the aforementioned engineering models is also shown.

Abstract: The paper describes in detail the function of the differential protection of the numerical relay device type RET670 of the company ABB. At the same time, the theoretical basis of the work of (stabilized) differential protection of energy transformers is presented, with a special emphasis on the specifics of its implementation in a numerical relay device type RET670 (such as, for example, a fault locator, recognition of the transformer being plugged into idle mode, etc.). The paper also presents the influence of various design and operating factors of power transformers on the vaporized operation of differential protection. Finally, the paper presents the method of parametrizing the mentioned protective function of the numerical relay device RET670 on a characteristic example of a two-winding and three-winding (three-phase) power transformer.

Abstract: The paper presents a mathematical model for analyzing the distribution of single-pole short-circuit currents (SCC) in passive parts (screens) of multi-system cable systems, consisting of single-core cables arranged in a triangular bundle. The aforementioned mathematical model is based on the method of equating a cable triple with a fictitious cable, using the method of mean geometric distances (SGU), with the application of the so-called matrix reduction coefficient, taking into account the electromagnetic coupling between neighboring cables (in the same cable trench). Based on the presented mathematical model, an appropriate computer program was developed, which was then applied to several different examples of multi-system cable lines.

Abstract: The paper describes the issue of determining the expected number of shielding failure flashover rates (SFFOR) on HV overhead lines (transmission lines) using the so-called of the classical electrogeometric model. A detailed theoretical basis for the development of the mentioned model is presented. The influence of the use of electrogeometric models proposed by different authors and the application of logarithmic-normal distributions of lightning current amplitudes proposed by different working groups (CIGRE, IEEE, IEEE T&D Committee) on the amount of the expected number of SFFOR was then analyzed. This was done on the characteristic example of HV transmission lines 110 kV (fir-shaped pole heads) and 400 kV (portal-shaped pole heads).

Abstract: Semiconductor nanowires have attracted significant attention in the last decade for their potential in improving existing or enabling novel devices. An important challenge in the field is to reproducibly control the electronic properties and to fabricate high purity nanowires. The goal of this thesis is to apply nanowires for the realization of field effect transistors and sensors, whose performance proves all the benefits of having high quality nanoscale materials. The nanowires used in this thesis are synthesized in our group and are mainly gallium arsenide (GaAs) nanowires grown by Molecular Beam Epitaxy (MBE) and germanium (Ge) nanowires grown by Chemical Vapor Deposition (CVD). Special in these nanowires is that they are synthesized by avoiding the use of gold in the nucleation and growth process, which should lead into higher purity and improved overall properties. The study is mainly realized by electrical measurements and by electronic microscopy in smaller part. In a first phase the nanowires are contacted in a 2-points configuration by means of optical lithography. In the following part, more complex methods, like Electron Beam Lithography (EBL), are applied in order to place the multiple contacts on the single nanowire. EBL technique enabled 4-point transport measurements which allowed accurate determination of the nanowire resistance and contact resistance. Even more than this, mentioned techniques allowed to understand what the effect of smaller size contact is and to realize devices in the size of few hundred nanometers. Additionally, we were able to realize more complex device geometries, for example by providing different gate configurations. We investigated different semiconductor materials (GaAs, Ge and Si), designed and realized multiple geometry field- effect transistors and sensors based upon them and characterized their properties, particularly regarding possible applications in future electronic devices architectures. Special attention was paid to ensure reliable and reproducible results.

Abstract: The paper presents the method of modeling the occurrence of backflashover on HV overhead lines (transmission lines) using the EMTP software package. The paper presents a short theoretical basis and the method of modeling individual components / parts of the overhead line that affect the occurrence of reverse jump (phase conductors, protective rope, pole, insulator chain, pole grounder, lightning current channel, etc.). The model in question, compiled in the EMTP software package, was then applied to the analysis of the phenomenon of reverse jump on the 110 kV HV transmission line, in the shape of a fir head with a steel grid column. The impact of changing individual transmission line parameters (eg the impact of changing the grounding resistance of the pole) on the occurrence of reverse jump was also analyzed.

Abstract: The paper presents the theoretical background of the so-called of the Chowdhuri-Gross model for the analysis of overvoltage conditions on an overhead line (power line) that occur as a result of a close lightning strike. It is an analytical model that, among other things, takes into account the influence of the steepness of the lightning current front on the realized overvoltages on the water (in the case of a close lightning strike to the ground next to the transmission line). On the basis of the aforementioned theoretical background, a corresponding computer program was developed in the paper, which then analyzed the influence of close lightning strikes on the occurrence of overvoltage conditions in typical MV transmission lines. In the analysis, the input parameters of the mentioned model were varied, such as e.g. height of water above the ground, distance of lightning strike from water, height of clouds above the ground, speed of lightning return strike, steepness of the front of the lightning current, amplitude of the lightning current, etc. water.

Abstract: The paper presents the phenomenology of upward and downward (positive and negative) lightning strikes. The problem of determining (estimating) the exposure to direct lightning strikes of modern wind turbines with a total height (tower + blade) exceeding 100 meters is described, with special emphasis on IEC 61400-24. An analysis of the expected proportion of upward lightning strikes in modern wind turbines was also carried out, based on Eriksson’s research, as well as recording the amplitudes of lightning currents that strike tall free-standing objects (e.g. radio towers). The influence of the expected proportion of upward lightning strikes on the assessment of the expected amplitude of lightning current that may be exceeded, e.g. once during a certain period of time (e.g. during the lifetime of a wind turbine), was then analyzed.

Abstract: As part of the dissertation, an analytical solution was developed for the transient response of a thin wire of finite length buried in the center with losses. The model is based on Pocklington’s integro-differential equation. Analytical treatment of the integral operator is performed by approximating the subintegral function, while the resulting differential equation is solved by applying the Laplace transformation. The solution of the equation obtained in the Laplace domain is transformed into the time domain by applying Cauchy’s residue theorem. The relation obtained in this way represents the impulse response of the wire. The reflection of the signal from the border of the two environments is taken into account by applying the reflection coefficient derived from the modified mapping theory. The exciting electromagnetic (EM) wave is modeled by sampling in the frequency domain and transferred to the time domain by inverse Fourier transformation. After that, a discrete convolution is performed between the incident wave and the relation for the impulse response of the wire, and the induced current for the concrete shape of the EM wave is obtained. The response to excitation by a current source connected to one end of the wire, which represents the grounding electrode, is also analyzed. The expression for the transient response of the electrode is derived in a similar way as for EM wave excitation. The induced current function along the electrode is obtained by performing an analytical convolution with the current source function. The obtained results, for both cases, are compared with the numerical results obtained by indirect modeling in the frequency domain in combination with the inverse Fourier transformation.

Abstract: The thesis deals with the problem of calculating the potential distribution at a certain distance from a point impulse charge as well as from a point source of impulse current, which are described using the Heidler approximation. When transitioning from the time to the frequency domain, there is no analytical solution to the Heidler approximation, so the function is approximated on the basis of the natural logarithm e, where the application of the collocation method at the point combined with the least squares method yields unknown values ​​of the weight functions for the slope factors n <3, 4, …, 15> . The second chapter describes the impulse point charge in the time and frequency domains using the Heidler approximation, the transition from the frequency to the time domain using the inverse Fourier transform, and the analytical and numerical expression for the potential distribution at a selected distance from the impulse point charge, in the time domain. The tables show the values ​​of the approximation coefficients a1k and β1k and the values ​​of the approximation coefficients a2k and β2k for different steepness factors n <3, 4, …, 15> . Examples are made for calculating the accuracy of numerical integration, which translates the potential function from the frequency to the time domain. In the third chapter, a point source of pulsed current is described using the Heidler approximation of the lightning current, and a numerical expression for the potential distribution at a selected distance from the pulsed point source of current, in the time domain. Examples are made in which the potential in the time domain is numerically calculated for the same pulsed current, for a selected distance of the observed point from the pulsed current source.

Abstract: This dissertation defines a methodology for identifying the parameters of a synchronous hydrogenerator during operation, based on measurements available within the hydrounit monitoring system at the Peruća HPP. The identification process uses data from recorded responses of generator variables in the small displacement regime, in quasi-stationary and transient states, with the application of appropriate estimation models and procedures. The identification process is divided into three steps, and the theoretical verification of each step, based on appropriate simulation responses, gave very good results for all parameters of the standard mathematical model of a synchronous hydrogenerator. For the identification of synchronous machine parameters based on measurements in operation, it is very important to accurately measure the load angle, to which one chapter of this paper is dedicated. A new method for determining the load angle is presented, which is based on measuring the armature voltage signal and the signal from the machine air gap sensor. An algorithm for determining the load angle in real time (“on-line”) has been developed, and its off-line variant is intended for carrying out the identification process. Since the identification of parameters does not require real-time processing, it was possible to apply subsequent digital signal filtering, which increased the accuracy of the algorithm. After theoretical testing, the validity of the proposed algorithm was verified by comparison with the procedure for determining the load angle based on measuring the rotor position using an inductive sensor. In the first step of the identification procedure, the parameters of the armature winding are determined. First, the leakage reactance of the armature winding is determined, for which there is no standard procedure yet. The paper uses a method based on measuring the induction in the air gap in no-load and short-circuit tests. A new procedure for determining the synchronous reactances of generators is defined, which requires only measurements in stationary operation, which was possible thanks to a special procedure for determining the reduction factor. The results of reactance measurements in a series of stationary points served as the basis for developing a machine saturation model. The model is defined in analytical form, where the synchronous reactances are defined as polynomials of two variables – magnetomotive forces in the longitudinal and transverse axes of the machine. The developed saturation model also includes the effect of transverse magnetization. Experimental verification of the model in the steady state was carried out based on measurements on a 34 MVA generator in the Peruća HPP. The developed saturation model was implemented in a standard mathematical model of the generator, which resulted in a saturated synchronous machine model. The estimation models for the second and third identification steps were corrected based on the developed generator saturation model. Based on the conducted analyses, it was shown that there is a large influence of saturation on the reliability of the estimation, especially in the third identification step in which the choke winding parameters are determined. Contrary to the results that can be found in the literature, it is shown that reliable identification of choke winding parameters based on the response in the small displacement regime is not possible. As for the second identification step, i.e. determination of the excitation winding parameters, the reliability of the procedure strongly depends on the noise level. Therefore, an alternative procedure was developed in which the application of the estimation algorithm was bypassed. The procedure was tested with appropriate measurements, resulting in satisfactory parameter accuracy and robustness of the procedure to measurement noise.

Abstract: The task of the thesis is to describe the characteristics of grounding systems of industrial plants. The first chapter of the thesis describes the grounding system. The methods of grounding the neutral point are resistive grounding, inductive grounding, resonant grounding and solid grounding. The selection of the neutral point of the system, grounding at points other than the neutral point of the system and the location of the grounding point of the system are described. The second chapter describes the grounding of equipment, where the basic objectives, the influence of electric shock, thermal influence, the basic concept and the difference of grounding equipment by type of use are mentioned. The third chapter deals with static and lightning rod grounding. The causes of static electricity, the possibilities of creating static charge and the conditions under which this occurs are described. The section on measurement and detection of static electricity lists and describes the instruments used. Static control methods such as grounding and bonding, humidity control, ionization, conductive footwear are listed. Lightning rod grounding describes the occurrence of lightning, the need for protection and equipment, factors that need to be taken into account when determining the size of lightning protection, and the terms for good protection. The fourth chapter describes grounding systems in distribution networks. Here are covered: designs of grounding conductors such as surface (horizontal, radial, ring, mesh), deep, foundation grounding conductors and the design of grounding systems, specific earth resistance and that soil resistance depends on the type, humidity, temperature: touch voltage, the highest permanent permissible touch voltage for alternating and direct current and step voltage. Finally, an example of grounding an industrial complex and an example of grounding a smaller facility are given.

Abstract: The thesis describes the problem of assessing the risk of damage from lightning strikes and based on this, results were obtained using the DEHNsupport software package. The first part of the thesis, which includes the second, third and fourth chapters, provides a theoretical basis for the calculation in the aforementioned program. After the introduction, the second chapter explains the concepts of damage and loss, as well as risk and its components, and provides factors that influence risk components. The third chapter lists the basic guidelines for risk management, which include identifying the object to be protected, the procedure for calculating the necessity and economic justification of protection, and the selection of protective measures. The fourth chapter discusses in detail the assessment of risk components for a building and provides all the formulas necessary for the assessment procedure. The concept of zones in a building is also introduced and the assessment of risk components in a building with multiple zones is explained. The second part of the thesis, which includes the fifth chapter, contains an introduction to the program, as well as the processing of examples using it. The calculation procedure using the mentioned program is attached in the appendix for each given building separately.

Abstract: The paper presents an overview of the available results of geotechnical investigations that precede the construction of substations of voltage level 35: 110: 220 and 400 kV, and the possibility of their application to solve the grounding system. The work is divided into four basic parts. As the work focuses on the implementation of investigative works, the first part deals with known research methods, the program, scope and types of soil testing. An overview of geophysical, geotechnical, geological, geomechanical and hydrological tests and the available results found in the geotechnical report - a document that processes and presents the state of the location for the construction of the substation - is presented. In the second chapter, specific geotechnical investigation works on the location of the future substation contained in parts of the geotechnical study are presented. A model for the inclusion of electrical engineers in the task of engineering geological research is proposed. His task would be active involvement throughout all three phases of the works, which by nature belong to the geological engineer. In the first phase of formulating the research, in the second phase of collecting data and in the third phase of analyzing and interpreting the data for the purpose of using them for the purpose of solving the grounding system. It also emphasizes the importance of solving the grounding system of substations and gives some specific examples of network grounding systems for which the results that can be perfectly used for the analysis and modeling were obtained during geological investigation works carried out for the very location where the future substation will be built. The third chapter presents examples of the analysis of the dynamic response of a vertical tube earthing switch, for which the results show influential quantities that, by coincidence, are excellently processed and can be optimized on based on the involvement of electrical engineers in the phase of conducting geotechnical works and preparing grounding studies. The fourth chapter presents examples of complex grounding conductors, laid in multi-layered soil with uniform characteristics in the horizontal direction, and calculations of potential and propagation resistance in the UZEM program. The conclusion provides examples of the possible use of geotechnical investigation boreholes for the application of vertical tube earthing rods, and concludes that when dimensioning earthing rods for lightning protection, it is advisable to use multiple shorter, spaced vertical tubes.

Abstract: The aim of the thesis was to describe the problem of electromagnetic coupling between the power and telecommunications systems in the event of a single-pole short circuit, as well as the influence of the power plant on telecommunications lines and the protection of the telecommunications system from harmful electromagnetic influences on the power system. The first chapter of the thesis describes certain technical regulations for the introduction of telecommunications lines into power plants. The second chapter describes the basic characteristics of telecommunications networks and lines, and we get to know fiber optics in more detail, which are in the true sense of the word the telecommunications lines of the present and the future. They are broadband lines, and their transmission capacity is very large, and their basic raw material is silicon dioxide (quartz), which is found in nature in huge quantities and is not expensive. The third chapter discusses the protection of telecommunications lines when introduced into a power plant, because both the power and telecommunications networks are becoming increasingly dense, and thus their intertwining is also becoming greater. We distinguish three basic types of influence of power plants on TK lines, namely galvanic, inductive and capacitive influence, and we are interested in general protection measures in case of dangerous and disturbing influences. In the fourth chapter, calculation methods for the introduction of TK lines into power plants are described. In the event of a single-pole short circuit, the hazard voltage may be higher than the maximum permitted hazard voltage. However, the TK system can be threatened by overvoltage coming from the power grid side and overvoltage coming from the TK network side. Based on calculations and insights on the ground, it is sometimes suggested to introduce a translator. In the last chapter, the management of the electromagnetic coupling of the electric power, TK and traction system is described, where we have the electromagnetic coupling of the electromagnetic field and cable, in zero and differential mode, coupling via common impedance and coupling between two cables in differential mode.

Abstract: The aim of the thesis was to determine the main uses and methods of the grounding system and to present the basic reasons for and against grounding. The first chapter of the thesis describes the grounding system. The methods of grounding the neutral point are resistive grounding, inductive grounding, resonant grounding and solid grounding. The selection of the system neutral point, grounding at points other than the system neutral point and the location of the system grounding point are described. The second chapter gives us the basic problem of grounding which relates to two contradictory criteria. The third chapter describes grounding systems in distribution networks. The chapter on the dimensioning of the grounding system discussed the criteria that need to be met in order to protect the facilities, but also people and animals. When dimensioning the grounding system with respect to current loads, it is determined by the fault current flowing through it. This method of dimensioning is used only when it comes to low-ohm grounding. The dimensioning of the grounding system with respect to grounding voltages was also discussed. The grounding voltage is equal to the maximum potential difference between the grounding system and the neutral earth. A special description is given of the part of this potential difference called the touch voltage or step voltage, which is dangerous for people. This voltage is proportional to the grounding voltage, so by reducing the grounding voltage, we also increase human safety. The chapter on the design of the grounding conductor discussed the resistance, design and shape of the grounding conductor. The last chapter provides a brief description of the standards used in this work.

Abstract: The first chapter briefly describes the topic of this thesis. The electromagnetic properties of soil are listed and their values ​​in free space, i.e. vacuum, are defined. After that, examples of systems on which the electromagnetic properties of soil can have a greater impact are listed and guidelines for the selection of measurement methods are given. The second chapter describes and defines the electromagnetic properties of soil. It can be seen that the resistivity of soil varies within wide limits and for different types of soil takes on values ​​from several Km to several thousand Km and that it decreases with increasing humidity and vice versa. Unlike resistivity, the specific relative dielectric constant varies within far smaller limits than the resistivity but also depends on the type of soil and frequency, like resistivity. In the third chapter, the selection of measurement methods is made and the marking system in them is defined according to IEE Std 356-2001, as well as the area of ​​application. The measurement methods are divided into location and laboratory. Each measurement method and measurement method is described individually. In the fourth chapter, laboratory measurements of the soil sample resistivity were performed using the U-I method, where the measured soil sample resistivity based on three measurements in different conditions was compared with the soil resistivity value that was measured in the field using the Wenner geoelectrical sounding method. The fifth chapter lists the literature, a list of symbols and abbreviations, and the conclusion reached based on the work on this thesis.

Abstract: Based on the available literature, this paper deals with the topic of insulation coordination from the point of view of selecting surge arresters. The protection of the power system and all the elements that make it up requires special attention, because poorly selected protection can result in very significant damage. Therefore, it is of great importance to properly and efficiently implement the insulation coordination procedure in order to achieve the best possible level of protection. In addition to the main element of protection (surge arrester) against voltage stresses, which is described in Chapter 8, insulation coordination methods are listed. Chapter 2 provides a brief overview of the voltage stresses to which the power system is constantly exposed, as well as their classification and characteristics according to IEC 60071-1. Their impact on the power system when they occur is described. Lightning strikes to the transmission line and the plant are also illustrated, which are shown in Figures 2.2 and 2.3. Chapters 3 and 4 deal with the classical, i.e. a statistical method of insulation coordination that allows us to see known and unlikely voltage stresses, as well as the selection and coordination of equipment for the purpose of the best possible protection. For the classic insulation coordination method, the voltage ranges of the equipment are listed, and the procedure for determining the tolerable insulation coordination voltage is described. The procedure for determining the risk of insulation failure according to the IEC 60071-2 standard is given for the statistical method. Figures 4.1 and 4.2 show the assessment of the failure risk factor and the probability of overvoltage. Chapter 5 deals with the process of insulation coordination according to IEC and IEEE standards. Principles and procedures according to IEC and IEEE standards are described in the mentioned chapter, while Tables 5.3 and 5.4 give standard insulation levels according to IEEE standards, and Tables 5.5 and 5.6 standard insulation levels according to IEC standards. Chapters 6 and 7 present the coordination of the insulation of the transmission line and the station. The impact of lightning on the line is shown, as well as its influence on the coordination of the insulation. Methods for improving water protection are also given. Chapter 8 describes the selection of surge arresters, primarily the metal-oxide surge arrester. The principle of operation of the surge arrester is described, as well as the determination of its operating voltage, and its protection zone. The current-voltage characteristic of the surge arrester is given, and the rules that must be followed when installing it in relation to the protected equipment are given.

Abstract: This thesis examines the issue of overvoltage protection of low-voltage networks. The emphasis of the work was on the selection of surge arresters and insulation coordination for overhead overhead lines and overhead self-supporting cable bundles. The ATP-EMTP software package was used to solve the selected examples.

Abstract: In this paper, one-dimensional and two-dimensional calculations for the unit internal impedance of a rectangular conductor are performed, as well as expressions for the factors of increase in the working resistance, inductance and impedance due to an increase in the frequency of the current flowing through the conductor. The introductory chapter of the thesis describes its task. The second chapter introduces Maxwell’s equations of the electromagnetic field in differential form and Maxwell’s equations in the harmonic electromagnetic field. The third chapter performs a one-dimensional calculation of the unit internal impedance of a rectangular conductor, using the derived expressions for the electric and magnetic field strengths in a conductive medium, using Poynting’s theorem. Furthermore, this chapter derives expressions for the factor of increase in the working resistance, inductance and impedance due to the skin effect in 1D calculations. The fourth chapter presents a two-dimensional calculation of the unit internal impedance of a rectangular conductor, and two different calculation methods are discussed, Rongo’s and Giacoletto’s. Furthermore, this chapter derives expressions for the increase factor of the working resistance, inductance and impedance due to the skin effect in 2D calculations. In the fifth chapter, the replacement of a rectangular conductor with a cylindrical conductor of equivalent radius using the same circumference method and the same cross-section method is presented. In the sixth chapter, the expression for the unit internal impedance of a cylindrical conductor is presented. In the seventh chapter, the dependence of the increase factor of the working resistance and impedance on the frequency of the current flowing through the conductor is presented in tabular and graphical form using selected examples. The examples presented relate to 1D and 2D calculations, and to the methods of replacing a rectangular conductor with an equivalent cylindrical conductor described in the fifth chapter, and to the cylindrical conductor described in the sixth chapter.

Abstract: The description of the EMTDC program, the method of modeling electrical networks, and the advanced features of the EMTDC program are described in the first chapter. The advanced features of the EMTDC program are the interpolation algorithm, the algorithm for removing numerical oscillations, the extrapolation algorithm, and the ideal branch algorithm. The second chapter describes the PSCAD program package, which represents a graphical user interface for the EMTDC program. PSCAD provides us with the ability to graphically construct the tested electrical and control circuits, run the simulation itself, and graphically display the simulation results. Each element of the system is displayed with the corresponding component located in the main library and which is copied from there to the project where it represents a component instance. The user enters the component parameters, and if necessary, can also change the component definition itself. To define transmission lines and cables, we use the transmission line and cable properties editor, in which we select one of the three available transmission line models and define the characteristics of the conductor and insulation, as well as the transmission corridor itself. In the third chapter, we describe the application of the PSCAD program package and concentrate on the propagation of voltage and current waves along transmission lines and cables. We calculate the transmission and reflection coefficients of waves when the wave impedance of the medium through which the waves propagate changes and compare the obtained numerical simulation results with the analytically calculated values. We have shown a way to model a surge arrester which, thanks to the property of voltage-dependent resistance, protects devices from excessive currents. The last example shows a lightning strike to the top of a transmission line tower and the voltage distribution along the tower.

Abstract: Renewable sources play an increasingly important role in global energy production. Wind farms are a desirable form of alternative energy source. Lightning protection has become of key importance for the safety and economy of large wind farms. This paper deals with the topic of protecting wind turbines and connecting cable lines from lightning strikes. The second chapter presents the basic characteristics of wind turbine drives, describes in detail the parts of wind turbines, and the general principle of operation of wind turbines. Connecting a wind turbine to the power grid is a significant problem. This leads to problems with grid operation. Trends in wind turbine development are also presented. The third chapter describes the protection of wind turbines from lightning strikes and the formation of protection zones. The protection system must be at the highest level, so the protection of individual parts and control systems of wind turbines has been additionally developed. The grounding system must enable the lightning current to be dispersed in the ground without causing dangerous voltages. To conduct lightning current from a wind turbine to the ground, it is necessary to have adequate grounding to limit overvoltages that can be dangerous for people and equipment. This is achieved by protective grounding that has a low impedance. This chapter describes the grounding system and all its features. The fifth chapter presents the overvoltage protection system of the low-voltage system of a wind turbine. Surge arresters and lightning current arresters in the 400/690 V system are specifically discussed. The selection of current arresters according to the type of protection is described. Examples of Dehn surge arresters and current arresters are given. The protection of the power system and all the elements that make it up requires special attention because poorly selected protection can result in very serious damage. Surge protection of the high-voltage system is discussed in the sixth chapter. This entire chapter is based on transformer overvoltage protection and the positioning of surge arresters for various cable sections. The main part of this paper is the protection of the connecting cable line of a wind farm built in poorly conductive soil. All options for protecting such a cable line are presented and discussed in detail, from the installation of surge arresters to numerical simulation of the locations of the surge arresters. An example of numerical simulation of the connecting 30 kV cable line between the 30 kV substation and the Orlice wind farm is presented.

Abstract: This paper describes the phenomenon of induced atmospheric overvoltages on power lines and low-voltage systems and protection against their harmful effects. The introductory chapter of the thesis describes its task. The second chapter defines overvoltage and its division into classes according to IEC 60071-1. The types and causes of transient overvoltages are also given. Special attention is paid to atmospheric overvoltages. The third chapter describes the formation of lightning and the electromagnetic field of the lightning return stroke. The lightning return stroke is responsible for inducing currents and voltages on lines. A chaining model is also given that describes the interaction of electromagnetic fields on lines. The fourth chapter describes the numerical models developed so far in the world for modeling induced atmospheric overvoltages. The fifth chapter provides examples of the implementation of Agrawal’s model in the ATP-EMTP software package. Simulations were made for different distances of lightning strikes from lines. The shape of the voltage on a ZnO arrester during induced overvoltages on lines is also shown. Chapter 6 discusses the influence of parameters on the shape of the induced electromagnetic pulse. The shape is influenced by many parameters, and the influence of the ground is particularly significant. Chapter 7 contains basic instructions for protection against LEMP. The division into protective zones and standard procedures for establishing electromagnetic compatibility of the object being protected are described.

Abstract: The first chapter presents the basic problems and dangerous situations in safety measures and grounding, and describes the circumstances that can cause electric shock. The second chapter lists the consequences of the action of electric current on the human body, the importance of the speed of fault clearing, and based on testing, the permissible values ​​of current that the human body can withstand are presented. In the third chapter, using the Thevenin equivalent, we obtained more accurate methods for calculating touch voltage and investigated the influence of adding gravel on touch voltage or step voltage. The fourth chapter discusses the characteristics from the aspect of soil resistance, dependence on soil structure and moisture, and describes two methods of geoelectric sounding. The fifth chapter determines the maximum current of the earth electrode using a reduction factor. The sixth chapter discusses the design of the earth electrode, which is aimed at increasing the safety of step voltage and touch voltage, and its improvement. The seventh chapter discusses the issue of grounding the substation fence and measures to reduce touch voltage. Chapter 8 covers the subject of grounding system design, describing two common methods of grounding installation and safety considerations during subsequent excavations.

Abstract: In this paper, the lightning current in the time and frequency domains is described using the Heidler function, where the function is approximated by exponential functions. The introductory chapter of the thesis describes its task. In the second chapter, the Heidler function is introduced as an approximation of the lightning current. During t<0, the lightning current is equal to zero. At t = 0, the lightning current begins to change. Since there is no analytical solution to the Heidler approximation from the transition from the time to the frequency domain, in the third chapter the function is approximated based on the natural logarithm e, where the collocation method at a point combined with the least squares method is used to obtain the unknown values ​​of the weight functions for the slope factor n <3, 4, …, 15> . The approximated function must satisfy the real function in m sampled points uniformly along the observation interval. It is determined that the approximation function consists of three parts: the approximation function for u < us , the approximation function for the range us <= u <= 1 and the approximation function for the range u > 1. In the fourth chapter, the values ​​of the approximation of the Heidler function for the frequency domain are obtained, where the transition from the time domain to the frequency domain is achieved using the inverse Fourier transform. By analyzing the real and approximated functions in the fifth chapter, a small percentage of error is obtained, which can be concluded from the presented Figures 5.1-5.13. It is seen that the approximation of the Heidler function follows the original function in its entire range. In the frequency domain for n=10, a high degree of accuracy is also achieved, which is confirmed by Figure 5.14. It should be emphasized that if any slope factor n <3, 4, …, 15> was taken, a high degree of accuracy would again be achieved.

Abstract: The paper describes the software package EMTP, which is used for transient analyzes in the power system. Special emphasis was placed on the application of the EMTP software package in the analysis of atmospheric overvoltages in high-voltage switchgear in open space. A brief overview of the modeling of individual components/elements of the switchgear for the purposes of the above-mentioned analysis of atmospheric overvoltages is given. The method of modeling the occurrence of an overvoltage wave on the switchgear, as a consequence of a direct lightning strike on the phase conductor of the incident transmission line, and as a consequence of the occurrence of a reverse jump on the incident transmission line is also presented. Finally, the application of the EMTP software package, for the aforementioned analysis of atmospheric overvoltages, was made on the concrete example of a typical switchgear TS 110/x kV.

Abstract: The task of this thesis was to study and describe the issues of grounding medium voltage networks, taking into account domestic and foreign experiences. The first chapter of the thesis is introductory. The second chapter provides technical recommendations for grounding the neutral point, describing the basic technical conditions and determining single-pole schemes for selecting a system for grounding the neutral point. The third chapter provides an analysis of the parameters for selecting the grounding method, taking into account voltage stresses, values ​​of ground currents and soil resistance, and the quality of electricity. Thermal stresses on equipment in the event of a single-pole fault are also taken into account. The next chapter describes the experiences of European Union countries with the issue of grounding MV networks. The experiences of France and Italy are taken into account. The fifth chapter gives us an insight into the variants of grounding MV networks. The method of grounding the neutral point is influenced by numerous factors. One of the basic ones is the magnitude of the capacitive current. The large number of methods used for grounding the neutral point in the world is the reason for the compromise between two main and mutually contradictory requirements, namely reducing the amplitude of the ground fault current, which can cause difficulties in detecting faults, and allowing larger amplitudes of ground fault currents, which makes it easier to detect a ground fault, but can cause dangerous touch voltages, and in this case the number of outages is also increased. Chapter 6 describes the criteria for grounding the neutral point of medium-voltage networks, where we concluded that the basic criterion when switching the network to operation with a grounded neutral point is the level of the capacitive ground fault current of the galvanically coupled network (IC).

Abstract: The basic task of this diploma thesis is the description of the basic settings of the protection of power plants against direct lightning strikes, with the focus of the work on the description of methods for modeling the arrester system, using an electrogeometric model. In the first part of the thesis, the features of the lightning current are described. From the point of view of protection, the lightning current is the most important quantity, which is why the peak value of the lightning current, the steepness of the lightning current, the charge of the lightning current, the square impulse of the lightning current and the density of the lightning current are described. It also describes the basic protection of power lines and plants using grippers, protective ropes, protective spark arrestors and surge arresters. The second part describes the technical features of the lightning protection system, which serves to reduce physical damage due to a direct lightning strike to the object. The protection system includes the gripper system, the drainage system and the grounding system. Lightning strike models are used for the analytical representation of the lightning strike protection system. There are two classic methods, the protective angle method and the empirical curve method. Based on them, an electrogeometric model was developed, which was further developed and applied, in the form of a modified electrogeometric model, in situations that occur in plants in order to arrive at the rolling ball method. This method is based on rolling an imaginary sphere of radius S over the surface of the plant. In the last part of the thesis, a stochastic model for assessing the effectiveness of lightning protection is described. The stochastic assessment of the effectiveness of lightning protection is based on the application of the Monte Carlo method, that is, on the application of a pseudorandom number generator.

Abstract: The idea of ​​the thesis is to design and simulate a single-pole short circuit on a triplex of a double line using ATPDesigner on a given network. The second chapter provides a general description of ATPDesigner and describes individual elements (generator, transformer, busbar, double line, excitation regulator, and electrical network) as well as the method of defining and managing these elements, accompanied by visual displays (print screen). The third part of the thesis describes an example of a single-phase and three-phase short circuit at the end of a line in a network offered in ATPDesigner, and simulations were performed on it, the results of which are shown in the pictures. The fourth chapter elaborates the target task of the thesis, the simulation of transient phenomena in the power system using ATPDesigner.

Abstract: The main idea of ​​the thesis was to get to know the dynamic characteristics of impulse earthing switches in more detail. Knowledge of the dynamic characteristics themselves is of great importance when modeling earthing systems. The special significance of these characteristics comes to the fore in the earthing of power systems (earthing switches for overhead line poles, earthing switches for antenna poles, etc.), and from atmospheric discharges. Namely, it is precisely during these very fast transient phenomena, i.e. at high lightning current gradients, that the dynamic characteristics of the earthing switch come into play. The behavior of the earthing system in these transient states must be known in order to achieve high-quality protection, i.e. to meet safety standards. The second chapter provides a description of various earthing designs, as well as the influence of soil characteristics, i.e. specific soil resistance. Different values ​​of this resistance are given for different types of soil. The third chapter presents an analytical description of the behavior of the earthing system for different time states, i.e. an analysis of parameters in a stationary or transitional or transient state. The designs of different geometries of grounding systems are observed. The fourth chapter is an introduction to the numerical solution of the problem. Namely, the definition of parameters is carried out, the discretization of the finite element is carried out, and other steps necessary for a discrete description of the state are carried out. Three different designs of grounding are observed, i.e. a horizontal strip, and two designs of conductors in the shape of a rectangle. In the fifth, final chapter, the results obtained experimentally, as well as the results achieved through other numerical models, are compared with the results of the numerical program used in the diploma thesis. Interpretations of examples are presented and conclusions are drawn.

Abstract: In this paper, one-dimensional and two-dimensional calculations for the unit internal impedance of a rectangular conductor are performed, as well as expressions for the factors of increase in the working resistance, inductance and impedance due to an increase in the frequency of the current flowing through the conductor. The introductory chapter of the thesis describes its task. The second chapter introduces Maxwell’s equations of the electromagnetic field in differential form and Maxwell’s equations in the harmonic electromagnetic field and describes their form in a conductive medium. The third chapter performs a one-dimensional calculation of the unit internal impedance of a rectangular conductor, using the derived expressions for the electric and magnetic field strengths in a conductive medium, using Poynting’s theorem. Furthermore, this chapter derives expressions for the factor of increase in the working resistance, inductance and impedance due to the skin effect in a 1D calculation. The fourth chapter presents a two-dimensional calculation of the unit internal impedance of a rectangular conductor. Furthermore, this chapter derives expressions for the factor of increase in the working resistance, inductance and impedance due to the skin effect in a 2D calculation. The fifth chapter presents the replacement of a rectangular conductor with a cylindrical conductor of equivalent radius using the same circumference method and the same cross-section method. The sixth chapter presents the expression for the unit internal impedance of a cylindrical conductor. The seventh chapter presents the dependence of the increase factor of the working resistance and impedance on the frequency of the current flowing through the conductor in tabular and graphical form using selected examples. The examples presented relate to the methods of replacing a rectangular conductor with an equivalent cylindrical conductor described in the fifth chapter, and to the cylindrical conductor described in the sixth chapter.

Abstract: The protection of electrical devices, elements of electrical installations and even the entire electrical power system is a very important branch of electrical engineering. The most common cause of electronic system failures are overvoltages that are superimposed on the operating signal, and reach the device and can cause its damage. The most common cause of overvoltage in electrical installations is atmospheric discharge, i.e. lightning strikes. Overvoltage protection used in electrical installations is a three-stage protection. The role of overvoltage protection devices is to protect electrical and electronic equipment and installations. Properly installed and coordinated external and internal lightning protection will successfully protect electrical installations and devices from overvoltages. In facilities connected to the low-voltage network, it is not necessary to install class I overvoltage protection devices, but a class II device installed behind the fuse and before the meter is sufficient. Class III overvoltage protection devices in overvoltage protection are installed by the owner of the facility himself. The diploma thesis explains the basic concepts and examines the issues of overvoltage protection at low voltage. The results of this thesis show how protection works in the event of overvoltage.

Abstract: This thesis deals with the problem of a point source of harmonic current in a multilayer horizontally complex medium, where the first layer is air, while the other layers belong to a multilayer soil. Special attention is paid to the case when the source and the observation point are in the same layer. The first chapter of the thesis is introductory and provides an introduction to the problem of a point source of transient current in a multilayer medium. The second chapter describes a multilayer horizontally complex model of the medium in which the distribution of transient potential is calculated. Most of the transient electromagnetic models developed so far are limited to homogeneous soil, or to a two-layer medium (soil and air). Only in the last few years have transient electromagnetic models appeared that take into account multilayer soil. The third chapter presents Maxwell’s differential equations for an alternating harmonically varying electromagnetic field. For a quasi-static field distribution, the Helmholtz differential equation is reduced to the Poisson differential equation, and then the Poisson differential equation is solved and the potential retardation is subsequently introduced. The fourth chapter describes the retardation factor and the calculation for the special case when the modulus of the retardation factor from the calculation turns out to be equal to unity. The fifth chapter presents examples of the analysis of the retardation factor when the source and the observation point are located in the same and in different layers of the medium. The sixth chapter presents a three-dimensional presentation of the modulus of the retardation factor in the observed four-layer.

Abstract: The task of this thesis was to examine the issue of protecting the power system from lightning strikes using metal-oxide surge arresters. Attention had to be paid to the selection of arrester characteristics and installation location. Chapter 2 describes the overvoltages that occur in the system and that pose a danger to the system and electrical elements. Chapter 3 presents the characteristics of MO surge arresters. The principle of operation and the protection zone are described, which is approximately similar for all types of arresters. Specifically, for MO arresters from ABB, their construction and the main division into EXLIM and PEXLIM types of MO arresters are presented. The current-voltage characteristic is presented, which is very specific due to its pronounced nonlinearity, which is also a great advantage of MO surge arresters over silicon carbide surge arresters. The third chapter also presents other characteristics of surge arresters that are very important for selecting surge arresters. Chapter 4 presents the procedure for selecting MO surge arresters, which is applied in Chapter 5, which presents specific examples of selecting MO surge arresters for 110 kV and 220 kV plants.

Abstract: In this paper, calculations of the grounding system were performed in two ways: using design methods and using the EarthHGriD software package. Based on the results obtained, a final conclusion was made on the accuracy of the calculation of the grounding system using design methods. The introductory chapter of the thesis describes its task. In the second chapter, we list the international standards for the design of grounding systems that were adopted in 1968 and have been valid in Croatia since September 30, 2008, when the application of the new standard HRN IEC 62305-3 ”Lightning protection Part 3: Physical damage to buildings and danger to life” began. The third chapter describes the basic characteristics of grounding, the effect of electric current on the human body, touch voltage and step voltage. Furthermore, this chapter describes the method of designating the grounding system, where in low-voltage distribution networks there are three types of networks with respect to the grounding system: TN, TT and IT system. The fourth chapter describes the tasks of grounding as well as the propagation resistance on the basis of which the grounding system is evaluated. Furthermore, the impact propagation resistance related to atmospheric discharge through the grounding electrode is mentioned, as well as the potential of the earth in the vicinity of the grounding electrode. The fifth chapter lists and describes the materials and shapes used for the grounding electrode, as well as the method of their installation. The sixth chapter presents the calculation of the grounding system using design methods for three types of grounding electrodes. The first type of grounding electrode is made using a horizontally placed strip grounding electrode, the second using a vertically placed rod grounding electrode in the form of grounding probes, while the third type is made using a combination of the previous two. The seventh chapter describes the operation of the EartHGriD software package. The eighth chapter presents the results obtained with the EarthHGriD software package and calculates the difference in the values ​​of the propagation resistance obtained by design methods, on the basis of which a conclusion will be drawn on the accuracy of the calculation of the grounding system using design methods.

Abstract: This paper describes the problem of calculating the electromagnetic field of power cables. From Maxwell’s equations, equations for calculating the magnetic field strength, magnetic induction and electric field strength due to currents in the phase conductors of a straight section of a cable line were derived. Based on the developed theoretical basis, a computer program was created for calculating the electromagnetic field of a straight section of a cable line. A total of five selected examples were solved using the computer program and the calculation results were analyzed. In the second chapter, the equations of the harmonic electromagnetic field, which follow from Maxwell’s equations for the harmonic field, are defined and described. In the third chapter, the numerical approximation of the longitudinal currents and potentials of the phase conductors of the considered straight section of a cable line is described. In the fourth chapter, the equations of the potential of the straight section of a cable line are derived. In the fifth chapter, the imaging of a point source of harmonic current located in the second layer of a two-layer medium is considered, where the first layer is air and the second layer is a homogeneous soil of known complex electrical conductivity. In the sixth chapter, the calculation of the magnetic field strength and magnetic induction of a straight section of an electric power cable line using the Biot-Savart law is presented in detail. The field is calculated in the plane of symmetry of the cable line section. In the seventh chapter, the algorithm for calculating the electric field strength of a straight section of an electric power cable line is described, assuming a grounded conductive cable screen. In the eighth chapter, a test example of a section of a single-core cable is solved, as well as selected examples of straight sections of a 10 kV and 35 kV cable line. The obtained results are graphically displayed and compared with the prescribed limit values ​​of magnetic induction and electric field strength in air above the cable line section.

Abstract: In the process of designing the grounding system of an electrical power facility, it is necessary to calculate as accurately as possible the expected values ​​of the danger voltage and the amounts of the electric and magnetic fields to which personnel and living beings in the immediate vicinity of the facilities under consideration will be exposed, both in a stationary state and in cases of short circuits and transient states of the system caused by lightning strikes. In order to make this possible, it is necessary to develop appropriate computer programs that will be able to model the above phenomena, with as few omissions as possible and as accurately and quickly as possible. In the dissertation, a new harmonic electromagnetic model of the conductor system in a horizontally arranged multilayer medium has been developed. The developed electromagnetic model takes into account the complete electromagnetic coupling between the conductors that can be located anywhere in the multilayer soil and even in the air. The conductors can be in any position relative to the soil surface. In addition, the conductors can be bare or insulated relative to the surrounding soil. This model includes, in addition to the calculation of the current distribution across the conductor system, the calculation of the potential at any point of the multilayer medium and the calculations of the hazard voltage. In addition, the model also includes the calculation of the distribution of the electric and magnetic field strength at any point of the multilayer medium for any frequency of interest. By upgrading the harmonic electromagnetic model, a new transient electromagnetic model of the conductor system in a horizontally stacked multilayer medium has been developed. The transition from the frequency domain to the time domain was performed using the FFT – IFFT algorithm. By applying the electromagnetic models developed here, it is possible to carry out new analyses and calculations that were not possible before. It is also possible to analyze the influence of soil layer parameters on the harmonic and transient behavior of the grounding system more accurately and qualitatively using simple examples. In addition, the grounding system in question may include metal structures in the air, which means that direct lightning strikes to GSM base stations, overhead power lines or parts of high-voltage switchgear can be simulated. The main original scientific contribution of the dissertation is the development of an efficient harmonic and transient electromagnetic model of a conductor system in a horizontally stacked multilayer medium. The scientific contribution of this work can be viewed much more broadly since, due to the universality of numerical methods, all developed numerical procedures can be successfully applied in the research and solution of a number of problems in various branches of technology.

Abstract: This paper sets out a theoretical basis and creates a computer program that successfully demonstrates the application of the finite element technique for harmonic and transient analysis of electrical circuits, as well as for the analysis of stationary and transient phenomena in the power system. According to the available literature, a completely new method for the analysis of transient phenomena in the power system is presented here. In Chapter 2, a simple and reliable algorithm for the analysis of both harmonic and transient electrical circuits is presented. The presented numerical algorithm is based on the finite element technique, using a solution logic analogous to the solution of fields in a continuum. In the terminology of the finite element technique, each branch of the circuit is considered as a finite element with two local nodes. The possibility of transient analysis of a linear circuit is demonstrated on a specific example of a linear circuit. The obtained numerical results are in excellent agreement with the analytical solution, which confirms the accuracy of the proposed algorithm. In Chapter 3, an algorithm for the calculation of short circuits in the power system using the finite element technique is presented. The elements of the power system are modeled on the basis of mathematical models that are natural for the stationary analysis of short circuits in the power system. For each type of finite element, a local system of equations was derived that serves to assemble the finite element with the rest of the network. On the example of a single-pole short circuit in the network, the finite element method was tested with the symmetric component method. It is important to emphasize the observed simplicity and generality in the development of a software package using the finite element technique in comparison with symmetric components. Using finite elements, it is possible to easily solve much more complicated problems, which is not the case with the symmetric component method. In Chapter 4, the possibility of applying the finite element technique in modeling electromagnetic and electromechanical transients in the power system is shown, using the logic of solving fields in a continuum. Mathematical models of finite elements are generally described by a system of differential equations. To perform the numerical integration of the above equations, we used the principle of the mean value of the integral ( -method). Each part of the system, or finite element, is represented by its local system of algebraic equations and has a certain number of local nodes, depending on the type of finite element. The number of nodes of a finite element is equal to the number of physical connections of that element to the power system. The generator model as a finite element was successfully tested with the EMTP-ATP software package on the example of a three-pole impulse short circuit. In Chapter 5, an analysis of electromagnetic and electromechanical phenomena in the power system was performed on the example of a single-pole short circuit on a double line, as well as on the example of a single-pole short circuit in the case of a power system with multiple generators. In Subchapter 5.1, we presented the short-circuit currents, overvoltages on the high-voltage side of the transformer, the electromagnetic torque of the generator, the excitation current of the generator, as well as the rotor circular frequency for the duration of the entire transient. In subsection 5.2, we have presented the results of the calculation, as a function of time, of the electromagnetic moments, reactive powers, excitation voltages, and load angles of all generators for the duration of the entire transient phenomenon. On selected examples, we have shown the possibility of applying the presented method in the analysis of various transient phenomena in the power system, as well as simple problem solving of a real power system, i.e. a system with a large number of generators, transformers, transmission lines, and other elements.

Abstract: This thesis deals with the problem of a point source of harmonic current in a multilayer horizontally complex medium, where the first layer is air, while the other layers belong to a multilayer soil. Special attention is paid to the limiting case when in one of the soil layers the harmonic current source becomes a direct current source. The first chapter of the thesis is introductory and provides an introduction to the problem of a point source of transient current in a multilayer medium. The second chapter describes a multilayer horizontally complex model of the medium in which the transient potential distribution is calculated. Most of the transient electromagnetic models developed so far are limited to homogeneous soil, or to a two-layer medium (soil and air). Only in the last few years have transient electromagnetic models appeared that take into account multilayer soil. The third chapter presents Maxwell’s differential equations for an alternating harmonically varying electromagnetic field. For a quasi-static field distribution, the Helmholtz differential equation is reduced to the Poisson differential equation, and then the Poisson differential equation is solved and the potential retardation is subsequently introduced. The fourth chapter describes the limiting case when the current source becomes DC and describes the potential distribution for a point source of DC in a multilayer medium. The case in which the point source of DC is located in one of the layers of a multilayer soil is considered. A point source of DC in air cannot be realized if the usual assumption is made that the air conductivity is zero. The fifth chapter describes a point source of transient current in multilayer soil. When observing a point source of transient current in multilayer soil, from a practical point of view, the most interesting thing to observe is the lightning current. Here, the description of the transient current using the Heidler function, the mapping of the transient current from the time domain to the frequency domain and the calculation of the potential distribution using the IFFT algorithm are presented. The sixth chapter presents examples of calculating the potential distribution along a line and at a single point for different positions of a point source, i.e. for the case when the point source is located in the first, second and third soil layers.

Abstract: Ball lightning is a rare and for now very difficult to explain phenomenon. In order to be able to understand the origin and nature of the phenomenon itself, the text deals with the usual form of lightning. Attention is also paid to unusual and unusual forms of lightning, the representative of which is the ball lightning itself. In the third chapter, full attention is paid to the characteristics of ball lightning, such as diameter, color, movement and similar properties attributed to it according to eyewitness reports, which are presented through statistics of the frequency of sightings. Phenomena similar to ball lightning were also mentioned, with which it could eventually be replaced. Considering the changing and unstable nature of the phenomenon that has been dealt with, many theories have been developed on the subject, which try to explain the phenomenon. Two options crystallized, models with internal and external energy, to which a part of the text is also devoted. And finally, what is perhaps the most important for the electrotechnical profession itself, an overview of the risks and dangers that can possibly threaten from ball lightning.

Abstract: This paper describes the problem of calculating the electromagnetic field of overhead power lines. From Maxwell’s equations, equations for calculating the magnetic field strength, magnetic induction and electric field strength due to currents in the phase conductors of a straight section of an overhead line were derived. Based on the developed theoretical basis, a computer program was created for calculating the electromagnetic field of an overhead line section. A total of three selected examples were solved using the computer program and the calculation results were analyzed. In the second chapter, the equations of the harmonic electromagnetic field, which follow from Maxwell’s equations for the harmonic field, are defined and described. In the third chapter, the numerical approximation of the longitudinal currents and potentials of the phase conductors of the considered overhead line section is described. In the fourth chapter, the equations of the potential of a straight section of an overhead line are derived. In the fifth chapter, the imaging of a point source of harmonic current located in the first layer of a two-layer medium is considered, where the first layer is air and the second layer is a homogeneous soil of known complex electrical conductivity. In the sixth chapter, the calculation of the magnetic field strength and magnetic induction of an overhead power line section using the Biot-Savart law is presented in detail. The field is calculated in the symmetrical plane of the overhead power line section. In the seventh chapter, the algorithm for calculating the electric field strength of an overhead power line section is described. In the eighth chapter, a test example of a single-conductor section is solved, as well as selected examples of overhead 110 kV overhead power lines of the type of girder without a protective wire and with a protective wire. The obtained results are graphically presented and compared with the prescribed limit values ​​of magnetic induction and electric field strength in air.

Abstract: The topic of this thesis was linear surge arresters, i.e. their features and application. As their task is to protect against overvoltage, in the second chapter the concept of overvoltage is explained, the basic types of overvoltage are mentioned and the concept of reverse jump, which is caused by atmospheric overvoltage caused by a lightning strike, is explained. The third chapter is dedicated to the classic ways of protecting the lines, which are no longer sufficient due to the increasing demands of consumers for high-quality delivery of electricity. The function of the protective rope and protective spark gap is briefly described, and the possibility of improving the grounding resistance is mentioned. In the fourth chapter, we moved on to the main topic of the diploma thesis, to line surge arresters. Since the main part of modern line surge arresters is actually a metal-oxide surge arrester, which has been used in plants for a long time, its main features are listed, its construction is explained and basic data is given. The general working principles and construction of two types of line surge arresters used in the world are described, and a comparison of their efficiency in protection against atmospheric surges is given. The success of line surge arresters in line protection is confirmed in the fifth chapter, which shows the results achieved by simulation in the ATP-EMTP software package. In the sixth chapter, some experiences in the application of surge arresters on power lines in the world and in the Republic of Croatia are presented, from which it is evident that the application of line surge arresters has achieved excellent results.

Abstract: The thesis deals with the problem of calculating the potential distribution at a certain distance from a point impulse charge as well as from a point source of impulse current, which are described using the double-exponential approximation. The unknown parameters of the approximation function of the impulse function are estimated using the Marquardt method, which was created by upgrading the Gauss-Newton method. The second chapter describes the impulse point charge in the time and frequency domain, the double-exponential approximation, the transition from the frequency to the time domain using the inverse Fourier transform, and the analytical and numerical expression for the potential distribution at a selected distance from the impulse point charge, in the time domain. The third chapter describes the point source of impulse current, the double-exponential approximation of the impulse lightning current, the method of calculating the unknown parameters using the Marquardt method, and the numerical expression for the potential distribution at a selected distance from the impulse point source of current, in the time domain. The discrete inverse Fourier transform does not provide satisfactory results when calculating the potential distribution at greater distances from an impulse point charge. Therefore, a numerical algorithm based on the trapezoidal rule with a non-uniform distribution was developed, which provides results with a very high degree of accuracy. Comparisons of the analytical and numerical curves of the potential of a point impulse charge show that these two curves completely overlap for all selected distances from the source. The developed numerical algorithm was then applied to calculate the potential of a point source of an impulse current, in the time domain, for a selected set of distances from the source, where there is no analytical solution in the time domain. The purpose of the developed numerical algorithm is its application as a test algorithm during the development of advanced numerical algorithms for transient analysis of grounding systems.

Abstract: The thesis deals with the problem of estimating lightning current parameters, which can be described using a double-exponential approximation or the Heidler function. The unknown parameters of the lightning current approximation function are estimated using the Marquardt method, which was developed by upgrading the Gauss-Newton method. The second chapter describes the characteristics and approximations of lightning current. The two most commonly used lightning current approximations are: the double-exponential function and the Heidler function. In the third chapter, an algorithm for estimating lightning current parameters described using the double-exponential function is developed and selected examples are solved. In the fourth chapter, an algorithm for estimating lightning current parameters described using the Heidler function is developed and selected examples are also solved. In all cases of estimating the parameters of the approximation function, two requirements must be met: the duration of the lightning current front and the half-life of the lightning current crest. In addition, possible additional requirements are: the total lightning current charge and/or the specific energy of the lightning current. In the process of estimating lightning current parameters, it is not possible to fully satisfy all the set conditions, which are satisfied by the Marquardt method. However, in all solved examples, deviations from the set conditions are negligible. In addition, the developed algorithms for estimating lightning current parameters are reliable because convergence is ensured in all cases, regardless of the given initial conditions.

Abstract: This paper describes the system for protecting ships from lightning strikes. The development of the protection system throughout history from the eighteenth century to modern systems is described. The parts of the system, their characteristics determined by standards and the methods used for calculating protection zones are described. The specific calculation of protection zones and the characteristics of the parts of the protection system are shown using the examples of a cargo ship and a sailing ship. The introductory chapter and the first three chapters of the thesis generally discuss the current and new standards, types of damage and consequences of losses from lightning strikes. The fourth chapter describes the design of a lightning protection system, from the arresters to the conductors to the earthing conductors. The methods of the protective angle and the rolling ball method are also discussed. The fifth chapter deals with the essence of this thesis. The characteristics of lightning, the danger of electric shock, the development of the system for protecting ships from lightning strikes throughout history, the components of the modern protection system are described and at the end of the chapter two methods used for designing a system for protecting ships from lightning strikes are presented. Chapter six contains advice that should be followed in case you find yourself in a storm accompanied by lightning. Chapter seven contains a method of calculating the system for protecting ships from lightning strikes. The calculation is presented for a cargo ship with a length of 150 m and a sailing ship with a length of 50 m (Adriatic Vila). The calculation is accompanied by ship drawings and pictures of the protection zones.

Abstract: In this thesis, expressions for the unit internal impedance of a cylindrical conductor and expressions for the factors of increase in working resistance, inductance and impedance due to an increase in frequency are derived. The first chapter of the thesis is introductory. The second chapter describes Maxwell’s differential equations of the electromagnetic field and Maxwell’s differential equations for the harmonic electromagnetic field. The third chapter describes the electromagnetic field in a conductive medium and the Maxwell equations that are valid in that case. The fourth chapter derives expressions for the electric and magnetic field strengths in a conductive medium and uses them to obtain expressions for the unit internal impedance of a solid cylindrical conductor, and then the impedance of a hollow cylindrical conductor. The fifth chapter presents asymptotic approximations of the Bessel and Neumann functions, which are introduced due to difficulties in numerically calculating impedance. The sixth chapter presents expressions for working resistance and inductance in direct current and uses them to obtain factors of increase in working resistance, inductance and impedance. They show how much the working resistance, inductance and impedance increase with increasing frequency. In the seventh chapter, the dependence of the working resistance, inductance and impedance increase factor on frequency is shown in tabular and graphical form using selected examples. Examples are given for copper, steel and aluminium conductors, as well as examples for conductors of different cross-sections. The difference between the increase factor of a solid and a hollow cylindrical conductor is also investigated, where it is seen that the impedance increase factor of a hollow conductor is smaller than the impedance increase factor of a solid conductor. This is especially pronounced for the protective conductive screen of a cable.

Abstract: The thesis describes the basic features of lightning current, with an emphasis on the analysis of the peak lightning current. The assumption was used that the peak lightning current can be represented by a Gaussian normal distribution, and the parameters of this distribution were taken from the international standard IEC 62305. After the basic parameters of the distribution of the peak lightning current were adopted, an algorithm was developed that can calculate the probability that the peak lightning current exceed the observed current value. In order to verify the correctness of the derived algorithm, the expression for the probability calculation itself was subjected to control using data also taken from the international standard IEC 62305. The improved algorithm proved to be satisfactory, and in accordance with the normative values, after which it was possible to start developing a program code that accurately describes the required probability expression itself. In addition to developing a more accurate algorithm for calculating the probability that the peak lightning current will be higher than the observed current value, the graduation thesis also developed an improved procedure for specifying the coordinates of the peaks and edges of the observed protected object, as well as the designed lightning protection. These data are printed in an appropriate way, so that they can be used in the program for evaluating the effectiveness of lightning protection. Improvements were introduced to the three-dimensional display of observed protected objects and protection, and their manipulation was facilitated. In order to test the effectiveness of the developed methods, selected examples were solved, the results of which can be found in the appendices of the thesis.

Abstract: The goal of this research was to design a multivariate method and a software tool that would allow transmission and distribution system operators, as well as other subjects in the electricity market, to predict the impact of a change in one quantity in the power system on another. The multivariate method implies the calculation of the mutual correlation of all considered dependent and independent variables, which forms a characteristic matrix of correlations. By analyzing the correlation matrix, a detailed insight into the characteristics of the system can be obtained. The new proposed view of the stochastic state of the power system implies that the system is viewed as a single closed space in which electrical and non-electrical quantities mutually “vibrate” . The result of the work is a defined new method that analyzes the „vibrating“ and forms a tool for its analysis in order to predict problems in the operation of the system and in the end to find a single quantity that would define the stochastic strength of the electric power network, all with the aim of making the most efficient use of existing and new elements of the network and of predicting new states based on the realized states system despite the risky and unpredictable market environment.

Abstract: This paper describes the procedure for creating a power map of a hydro generator connected to a rigid grid using the LabVIEW software package. In addition to creating a program that enables a graphical display of the power map, the paper also analyzes the limits of the power map in detail. Verification of the obtained results was performed by comparing them with the results available in the relevant literature using the generator parameters in the Peruća HPP.

Abstract: The paper describes the procedure for commissioning the thyristor rectifier Simoreg which is used to power the excitation winding of a synchronous generator. The synchronous generator used was connected to a rigid network via an appropriate choke, and the behavior of the control circuit of the excitation current, armature voltage and reactive power of the generator was analyzed in various stationary and dynamic operating modes. The corresponding results were compared with similar results available in the relevant literature.

Abstract: The paper describes the modeling and simulation procedure of a synchronous generator connected to a rigid grid via a choke using the MATLAB/Simulink software package. In addition, the thyristor excitation system was analyzed together with the excitation current, armature voltage and reactive power control circuits of the generator. Verification of the simulation results was performed by comparing them with the results available in the relevant literature using the generator parameters in the Peruća HPP.

Abstract: structure of small hydroelectric power plants, planned technical characteristics of MHP Peruća, hydrological and energy basis and possible production of MHP Peruća, profitability of construction of MHP Peruća

Abstract: This paper describes the modeling, determination of parameters, measurement and analysis of cage asynchronous motor failures, such as inter-turn short circuit, rotor rod rupture and ring rupture. The mathematical model of an asynchronous motor with a non-sinusoidal field in the air gap is based on the calculation of chained fluxes with the help of the winding function, taking into account the spatial harmonics of the magnetomotive force. All parameters are calculated from the actual winding geometry and standard parameters obtained from classic short-circuit and no-load tests. Special attention is paid to the stator and rotor differential leakage reactance and the influence of beveling of the rotor rods. A standard mathematical model was used to verify the non-sinusoidal mathematical model. The parameters of both models were confirmed by measurements on a laboratory model. The most common fault is an inter-turn short circuit, and it is modeled by introducing a fourth phase whose number of turns depends on the location of the short circuit. The new phase is galvanically connected to the phase in which the fault occurred, however they belong to different electrical and magnetic circuits. The mathematical model for simulating rotor faults remains unchanged compared to the model of a healthy motor. Since the dimensions of the rotor cage do not change during these faults, all parameters, except for the rotor bar resistance, remain the same in both models. In order to investigate the star point voltage, computer simulations of non-sinusoidal models with different numbers of rotor bars were performed. Three laboratory models were built for the purpose of experimental verification of the results. The first laboratory model was realized for the purpose of measuring the voltage star point of a healthy motor. The voltage is measured between the star point of the motor and the star point of a well-balanced load. For the harmonic analysis of the star point voltage, a fast Fourier transform algorithm was applied. In addition, the frequency of the interharmonic measured in the star point depends on the rotation speed, so it was used to measure the rotation speed. Other laboratory The model was implemented for measuring the star point voltage of a motor with an inter-turn short circuit. On the stator winding specially made for this purpose, five disconnections were performed on the winding of the same phase. By connecting the external resistance between the taps, the resistance of the inter-turn insulation is simulated. At the moments when the resistance is connected, pulses appear in the constellation voltage, and a wavelet transformation was used to detect them. The third laboratory model was realized in order to measure the voltage of the motor constellation with a broken rotor rod. The frequency spectrum of the constellation voltage shows that, compared to a healthy motor, the interharmonic near the third harmonic increases more than fifty times, which is a clear sign of rotor rod breakage.

Abstract: The thesis presents the designs of the most commonly used compensation devices in medium-voltage networks. An analysis of voltage-current conditions during interruptions and short circuits in compensation devices, which cause their asymmetry, was carried out. In this way, the values ​​of indicative quantities for setting numerical protection were determined. For a specific example of a compensation device installed in a 10(20) kV plant, a relay protection system is presented.

Abstract: U ovoj se disertaciji obrađuje problematika primjene predikcijskih regulatora na procese s više ulaza i više izlaza (MIMO procesi). Ukratko se opisuje povijesni razvoj predikcijskog upravljanja za procese s jednim ulazom i jednim izlazom (SISO procese). Detaljno je analiziran poopćeni predikcijski regulator, te izveden zakon upravljanja ovog regulatora. Iznesena su pravila za podešavanje parametara poopćenog predikcijskog regulatora, te je predložen način podešavanja težinskog koeficijenta upravljačkog signala. Opisani su matematički modeli procesa s više ulaza i više izlaza, te iznesena osnovna pravila za uparivanje ulazno-izlaznih veličina. Također je predstavljeno uobičajeno rješenje za rasprezanje regulacijskih petlji pomoću rasprežnih kompenzatora, te su analizirana svojstva sustava upravljanja s primjenom rasprežnih kompenzatora. Detaljno su analizirane različite strukture predikcijskih regulatora MIMO procesa: zavisni i nezavisni višepetljasti poopćeni predikcijski regulator, višepetljasti poopćeni predikcijski regulator i poopćeni predikcijski regulator u prostoru stanja. Razmatrane su mogućnosti primjene pojedinih regulatora kod različitih MIMO procesa. Posebna pažnja posvećena je razvoju algoritama za rasprezanje regulacijskih petlji kojima se unapređuje osnovni algoritam predikcijskog regulatora. Opisani su postojeći pristupi s korištenjem rasprežnih kompenzatora ili modificirane kriterijske funkcije. Predložen je nov algoritam za rasprezanje zasnovan na adaptaciji težinskog koeficijenta regulacijskog odstupanja kod promjene vrijednosti referentnih veličina. Prednost predloženog algoritma očituje se u njegovoj jednostavnosti, maloj numeričkoj zahtjevnosti, i univerzalnosti primjene kod regulatora zasnovanih na minimizaciji kriterijske funkcije. Razmotrena je upotreba predikcijskih regulatora u realnim industrijskim procesima. Opisana je neophodna nadzorna ljuska regulatora, te postupci identifikacije parametar procesa s više ulaza i više izlaza kod samoudešavajuće izvedbe predikcijskog regulatora. Konačno, teorijska analiza iz rada je potvrđena i eksperimentalnim istraživanjima na laboratorijskom pogonu autonomnog sinkronog generatora i modelu sustava za upravljanje elektrodama lončaste elektrolučne peći. Provedeni eksperimenti sa samoudešavajućim poopćenim predikcijskim regulatorima potvrđuju razmatranje o primjeni predikcijskih regulatora na MIMO procese, te kvalitet predloženog algoritma za razvezivanje regulacijskih petlji.

Abstract: The asphalt production process is discussed and all parts of the production process are described in detail. Special attention is paid to the distribution of cold aggregate into hot aggregate silos, and conditions for asphalt production without pouring material from the silos are derived. An aggregate dosing control system is developed and described, and a regulator for this system is designed. PID structures and structures with Smith predictors are considered. The proposed solutions are confirmed by simulation analysis in the MATLAB/SIMULINK software package.

Abstract: The paper analyzes one of the structures of vector control of an induction motor (AM) without a speed measuring term. This vector control system of an induction motor is based on a reference model with an adaptive system (Model Reference Adaptive System, MRAS). The rotor magnetic flux vector is the physical quantity that is estimated by the voltage (stator winding equation) and current model (rotor winding equation). The current model was chosen to be reference, and the voltage model was adaptive. The difference in the estimation of the rotor magnetic flux vector obtained from these two models is used to estimate the rotational speed and identify the stator ohmic resistance. The computer algorithm that, in the described way, in calculations and in real operation, estimates the rotational speed and identifies the stator ohmic resistance is called the observer. This observer is based on the theory of adaptive control. The inter-inductance of the analyzed motor changes due to saturation in the iron, especially at lower frequencies of the supply voltage. Therefore, in the vector control system based on the MRAS theory, the influence of the error in the estimation of the motor’s mutual inductance, which is a parameter in the observer, was investigated, and it directly affects the indicators of the quality of the speed regulation and the stability of the vector control system. A simulation computer program for the AM vector control system was created, taking into account the saturation of the main magnetic circuit. Step changes in the speed reference and load torque were simulated. The mathematical model of the vector control system was created in a synchronously rotating d, q coordinate system related to the rotor magnetic flux. For the purposes of experimental research, a laboratory model of the AM vector control system was created. The vector control system is implemented using the digital signal processor TMS320F240, which is built into the control card DS1104, manufactured by dSpace. The frequency converter is self-made with IGBT transistors (100 [A]) and with a constant DC intermediate circuit voltage. In this work, it was chosen that the control of IGBT transistors is performed according to the algorithm of vector PWM modulation (eng. Space Vector Pulse Width Modulation, SVPWM). Spectral analysis of the calculated and measured AM stator current vector showed that the amplitudes of the higher harmonic components are negligible compared to the amplitude of the fundamental harmonic. For this reason, the inverter with vector PWM modulation, from the point of view of speed regulation, can be idealized in such a way that instead of the stator voltage vector, the reference voltage vector of the inverter is considered. In this dissertation, the estimation of the rotation speed of the AM was analyzed using a simple two-layer neural network and multi-layer static neural networks of different structures. Elements of the theory of neural networks are presented in this paper. The speed estimated by the neural network is sensitive to the accuracy of the estimation of the mutual inductance, which is given as a parameter in the vector control system. Errors in the estimation of the mutual inductance of the motor lead to distortion of the speed estimated by the neural network. This distortion is manifested in the fact that the speed estimated by the neural network differs from reference speed and that in addition to the DC component, higher harmonic components also appear in the speed. These higher harmonic components are more pronounced the greater the error in the estimation of the mutual inductance Lm. The frequency of the first higher harmonic in the estimated speed fN1 is equal to the frequency of the first harmonic of the supply voltage vector-controlled induction motor. As a quality criterion for estimating the rotational speed by a neural network in the steady state of an AM, an analysis based on the calculation of the mean value and standard deviation of the rotational speed estimated by the neural network has been proposed. It is shown that the ohmic resistance of the stator of a vector-controlled AM can be identified by the analyzed observer only in stationary operating modes, while in dynamic operating modes this identification is unsatisfactory. For the purposes of stability analysis, a linearized model of the AM and a linearized model of the control system were created. This The two models are combined and the transfer function of the vector control system at the reference speed is obtained. By observing the motion of the zeros and poles of this transfer function in the complex plane, one can conclude about the stability of the vector control system. It is shown that the best indicators of the quality of speed regulation are achieved if motor inductance estimated without error. If the inductance is estimated at a value smaller than the actual ( ), the motor speed first becomes oscillatory, and then the control system becomes unstable. If the intermediate inductance is estimated to be greater than the actual ( ) then there is a static deviation of the reference speed from the actual speed, and the settling time of the speed response to a sudden change in the speed reference is approximately twice as long as when there is no error in the estimation of the AM intermediate inductance.

Abstract: The paper describes the process of modeling and simulating an electromechanical system such as a synchronous generator loaded with a three-phase diode bridge using the MATLAB/Simulink software package. In addition, a system consisting of two generators (the main generator and its exciter) was considered, both with a diode bridge in the armature circuit. For the mentioned generator system, simulations were made in selected stationary and dynamic modes of operation. The simulation results were verified by comparison with the results available in the respective literature. The paper also provides an overview of alternative software packages that are used for similar purposes.

Abstract: The paper describes a parameter identification procedure based on an asynchronous motor start-stop experiment. The problem of rotor resistance identification is experimentally addressed, taking into account the rotor cage temperature, both in classical measurement procedures and in identification procedures.

Abstract: The electromagnetic conditions in an asynchronous squirrel cage motor when one rod is broken are theoretically analyzed. The harmonic composition of the stator currents in a healthy motor and a motor with one rod broken on the rotor is measured on a laboratory model. The possibility of detecting a rod break is analyzed.

Abstract: The paper describes the parameter identification procedure based on the start-up test of an asynchronous motor. In addition, the problem of identifying the rotor resistance of an asynchronous motor based on the voltage recording at the stator terminals during the stop test is theoretically and experimentally addressed. The identification results are verified using classical measurements during the no-load and short-circuit tests. A three-phase 4-pole asynchronous squirrel-cage motor 2.2 kW, 400 V, 50 Hz was used for the simulation and measurement purposes.

Abstract: Planning the operation of the electric power system (EES) represents a very complex problem conditioned by numerous techno-economic parameters, largely stochastic in nature, and aims to create an EES operation plan in the observed period that will result in the lowest costs in the system while meeting the required level of operational safety system. Medium-term planning of EES work, which in this work implies a time period of at least one month to a maximum of several months, is conditioned primarily by the size and structure of production capacities in EES, but also by the organizational conditions in which it takes place. Medium-term planning must always be a variant, in such a way as to determine the optimal plan with regard to a wide range of possibilities conditioned both by stochastic parameters (hydrology, thermal power plant outages, changes in consumption) and by planning decisions at the medium-term level (use of reservoirs, engagement of thermal power plants, import contracting /electricity export, etc.). Through the research in this paper, a simulation-optimization model of EES work planning at the daily level was conceived and realized, on the basis of which different synthesis models of the medium-term work plan of EES were defined. The medium-term work plan provides variant work balances of the EES, which are the basic basis for important planning decisions such as import/export of electricity, fuel procurement, changes in the planned regime of use of reservoirs, etc. The medium-term planning models of the EES work are elaborated on three levels: a pure deterministic model with the possibility of variant analysis, an upgrade with a probabilistic model for the calculation of expected production, variable costs and safety parameters of the EES operation, and finally an upgrade with a Monte-Carlo simulation model that provides the greatest possibilities for creating a medium-term EES work plan for an arbitrarily selected set of input parameters given by appropriate probability density functions. All levels are accompanied by appropriate examples that show part of the results of the medium-term work plan for a concrete example of the work planning of the EES of Croatia. The fundamental area of ​​application of the conducted research primarily refers to the operational medium-term planning of the operation of a smaller-sized mixed hydro-thermo system, as a basic tool for the decision-making model and energy-economic-security valorization of decisions about the way to use available production facilities, water from reservoirs and decision-making on the medium-term purchase or sale of electricity, which includes an appropriate analysis of possible economic risks that follow from planning decisions. The proposed methods of medium-term planning of EES work can be equally well used in the centralized-monopolistically organized electricity industry, as well as in the deregulated one. to the market-organized EES, clearly with a corresponding extension that includes models for forecasting electricity prices in the observed planning period. In addition, the results of the conducted research showed additional possibilities of application in areas of EES operation planning that are not primarily related to medium-term planning, such as daily EES operation planning, planning of the construction of new production facilities, testing and operation planning of individual power plants/ hydropower subsystems, etc.

Abstract: This paper describes a parallel active power filter that cancels higher harmonics of current in the electrical network. The active filter uses a three-phase inverter to inject into the network an appropriate current waveform that will cancel harmonic distortions so that the network current is practically a sinusoidal waveform. Control is performed in the time domain using three independent hysteresis regulators that generate control signals for the inverter based on reference currents. The reference current is defined as the difference between the actual load current and its fundamental harmonic. In order to obtain a reference current without time delay, a filter system with a predictive structure consisting of a cascade connection of a low-pass digital Chebyshev filter and a predictive digital filter was used to determine the fundamental harmonic. The low-pass filter extracts its fundamental harmonic from the load current, and the predictive filter cancels the delay introduced by the low-pass filter. The coefficients of the predictive FIR filter for predicting a sinusoidal signal were determined using Lagrange multipliers. By subtracting the extracted fundamental harmonic of the load current from its current value, the reference current of the active filter is obtained without time delay. Computer simulation of the mathematical model of the filter system with a predictive structure has confirmed its applicability in the system for determining the reference current of the active filter. Simulation of the operation of a single-phase and three-phase active power filter with predictive determination of the reference current in stationary and dynamic operating modes has determined the basic characteristics of the active filter. For the purpose of experimental verification of the results, a laboratory model of a parallel active power filter with a nominal power of 16.5 kVA was created based on an inverter implemented using an intelligent power module (IPM) with 6 IGBTs. The algorithm for determining the reference current using the filter system with a predictive structure has been implemented on a DSP, and current regulation has been achieved using three independent hysteretic current regulators. The efficiency of the implemented laboratory model of the active power filter has also been confirmed experimentally. The measurements obtained by connecting the active filter to the electrical network with different types of consumers were compared with the simulation results. A very good agreement between the experimental and simulation results is observed. It has been shown that the active filter successfully cancels current harmonics both in the stationary mode and in the dynamic mode of operation of the electrical network.

Abstract: The paper deals with the problem of optimizing the multipurpose use of seasonal storage pools in the power system with a significant share of hydropower. The fundamental goal is to achieve maximum profit from different ways of using water, taking into account all possible limitations. The main difference between the proposed method and the usual method of pool management is in the treatment of other water users. Other users can continue to be modeled as constraints (eg water supply to the population) but also as equal participants in the realization of profits. The modeling of other water users and their objective functions is, at least for now, quite simple compared to the modeling of hydropower plants and their profits in the power system. All input variables such as inflows into pools, intermediate inflows, demands of electricity consumers, etc. are modeled deterministically. In the proposed method, the optimization problem for S basins is broken down into S subproblems in which one basin is optimized while the discharges of the other basins are kept temporarily constant. The solution of the subproblem, i.e. the determination of the optimal flow distribution on one reservoir, can be found by a suitable optimization procedure for solving nonlinear optimization problems with constraints. Therefore, a long-term water use policy or a solution to a global objective function results from successively solving a series of subproblems described by local objective functions. By decomposing the objective function into two levels, we make the optimization problem simpler and solvable with proper management of the entire procedure and the use of a suitable optimization method for frequently solving the local objective function. The local objective function contains fewer variables, has a simpler structure, and is therefore easier to solve. Thanks to the decomposition of the problem, each phase of the calculation can also include some less influential parameters, which were previously neglected. The possibly longer duration of the entire budget is an insignificant factor when solving problems of this type. The proposed method is applicable for long-term planning in the conditions of the open market of production and sale of electricity due to the possibility of calculating the electricity balance with different electricity prices in certain time periods. The proposed method was tested on several examples.

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Abstract: Grounding conductors of electrical installations are an important part of the power system. Most mathematical models for modeling grid grounding conductors are based on the assumption that the current is direct. This assumption is used because harmonic current, as well as lightning current, require more complex mathematical models. One of the problems in creating new mathematical models that are able to take into account harmonic current or impulse current is taking into account the influence of heterogeneity of the medium. In this diploma thesis, an approximation based on the mapping of a point source of harmonic current on the boundaries of a horizontally stacked multilayer medium, consisting of air and at most three layers of soil, is developed. The presented mapping method is approximate because the potential retardation is neglected. In the paper, analytical expressions for the potential distribution in a single layer of a multilayer medium when the point current source is located: a) in the air, b) in the first layer of soil, c) in the second layer of soil are derived. The potential retardation can be partially taken into account by subsequently considering each source and its images, obtained by the imaging method, because the source and its images represent a set of point sources in a homogeneous and unbounded medium that has the characteristics of the considered layer.

Abstract: In this paper, a theoretical basis has been established and a computer program has been created that successfully demonstrates the application of the finite element method for calculating the propagation of a traveling wave in a conductor system with lumped and distributed parameters in the time domain.

Abstract: This paper presents the theoretical basis for more accurate calculation of currents and potentials along large mesh earthing conductors or earthing systems as earthing conductor discharge fields in homogeneous soil. It takes into account the influence of harmonic time changes of the power source. The calculation is limited to low frequencies. The introductory chapter highlights the need for more realistic and accurate analysis of large earthing systems as a prerequisite for optimal and safe earthing of power plants. To solve the task set, the development of a new method and an approach to the problem using the theory of electromagnetic fields and the theory of electric circuits are proposed. The second chapter contains an overview and commentary on several relevant methods that are currently used in the analysis of so-called non-equipotential earthing conductors for quasi-stationary conditions. The determination of the distribution of transverse leakage currents and longitudinal currents along underground bare conductors in all of the above methods is based on the segmentation of these conductors. The methods differ significantly from each other in the way in which the mutual impedances of the segments are included in the calculation and in the expression used to determine the impedance value. The third chapter presents general relations for the responses of a horizontal and vertical infinitesimal electric dipole in an infinite homogeneous conducting medium. Immediately after this, analogous relations are given for a dipole in a lower homogeneous conducting half-space with air (or any other medium) as the upper medium. These last relations, which contain Sommerfeld integrals, are quite general within the framework of the thin wire assumptions and are not frequency-limited. The fourth chapter presents analytical approximations of the Sommerfeld integrals that are valid in a certain low-frequency range. In addition, even simpler analytical expressions are developed that can be used in calculating the mutual impedances of segments for quasi-stationary conditions. However, they are valid, with a certain error, for a limited range of distances between the source point and the observation point. The limiting distances are shown in the diagrams as functions of the specific electrical resistivity of the soil with a given percentage error of the absolute value of the approximation, and for a frequency of 50 Hz. In Chapter 5, definitions of different mutual impedances between two thin, cylindrical, finitely long and uninsulated segments located in a homogeneous conducting unbounded medium or in a conducting half-space are given and discussed. Due to the variability of the amount of current along such a segment, the classical definition of mutual impedance is not applicable. Instead of the concept of general (generalized) mutual impedances, a concept with separate longitudinal and transverse mutual impedances is introduced. They use the average values ​​of the current or potential of the segment in their definition expressions, respectively. In Chapter 6, the development of a mathematical model for calculating the distribution of potentials and currents on a mesh non-equipotential grounding conductor buried in a homogeneous conducting half-space is presented in detail. In the process of solving the IDJ of the alternating electromagnetic field of a system of thin conductors, the matrix method with the Galerkin method and the linear function of approximation of the longitudinal current of the segment is first applied. The resulting system of linear segment equations was then modified and the concept of longitudinal and transverse mutual impedances of segments, described in Chapter 5, was introduced. Then, a special matrix relation was found which, in the linear approximation of the current, connects the segment currents (longitudinal and transverse) and the node currents imposed on the grounding system. Finally, this matrix relation allows setting up a system of linear algebraic equations with the node potentials as the only unknowns. The distribution of currents across the grounding system is determined after the node voltage vector is determined using the matrix relations of the theory of electric circuits and a special form of the node-branch incidence matrix. After determining the transverse currents, it is possible to calculate the potentials on the ground surface. Chapter 7 refers to analytical and numerical procedures for determining the values ​​of the segment self-impedances as well as different types of mutual impedances between two straight segments of grounding conductors. Chapter 8 presents a block flow diagram of a computer program for calculating large mesh grounding conductors or grounding systems. In Chapter 9, several characteristic examples illustrate some of the possibilities offered by the computer program in the analysis of large earthing systems. A comparison of some available measurement results with results calculated using various theoretical models is also carried out. The conclusion highlights the scientific contribution of this work, and some general recommendations for the calculation and design of large earthing systems are also given.

Abstract: The paper presents a method for estimating the rotation speed and position of the rotor of an electronically commutated motor (EKM). When designing the method, known estimation procedures for EKM, synchronous motor with permanent magnets on the rotor and asynchronous motor were analyzed from the literature. The presented method is based on the application of the extended Kalman filter (PKF) and a discrete motor model with line voltages. When applying the PKF, it was necessary to solve a number of specific problems, which are mainly related to the characteristic waveforms of voltages and currents of EKM. The measured quantities are line voltages and motor currents that are not filtered using analog filters, which is otherwise common with similar methods. This is made possible by synchronizing the measurement and control of the transistors of the converter so that the influence of noise on the measured values ​​is minimized at the time of measurement. The mean voltage value during the discretization period is determined by combined measurement and calculation procedures. In this calculation, the intermittency of the transistor is used, which is calculated by the predictive current regulator at the beginning of the discretization period. This controller is based on a mathematical model of the engine. Due to the application of PKF, special attention was paid to the selection of covariance matrices of system and measurement noise. The measurement noise covariance matrix depends on the accuracy of the current measurement and its members are constant throughout the estimation process, while the members of the system noise matrix depend on the accuracy of the motor model and the accuracy of the voltage determination, and change adaptively depending on the motor operating mode. Optimization of the coefficients of the system noise matrix was carried out by simulation and experimental procedures. In order to obtain basic knowledge about the quality of the presented estimation method, a simulation was carried out on a digital computer. For this purpose, a computer program was created that simulates the electric motor drive with EKM and the estimation procedure. Two variants of the program for simulating the estimation procedure were created: (1) with constant engine parameters and (2) with simultaneous estimation of state variables and engine parameters. The simulation results of stationary and dynamic modes of operation with constant engine parameters showed that it is possible to estimate the speed and position of the EKM rotor with high estimation accuracy. The sensitivity of the estimation results to the motor parameters was tested by simulation, and significant sensitivity of the results to the stator winding resistance and the electromotive force constant was determined, while the results were not significantly sensitive to the stator winding inductance. The influence of the covariance matrices of the system and measurement noise on the estimation results was also analyzed. The simulation The possibility of simultaneously estimating state variables and each motor parameter individually was investigated, and satisfactory results were obtained in estimating the stator winding resistance and the electromotive force constant. Before experimentally verifying the estimation results, the motor parameter identification procedure was carried out. This procedure consists of experiments and numerical calculations. , and is based on minimizing the difference between measured and calculated quantities in the time domain. To determine the parameters of the stator winding, it is important to conduct an experiment that ensures that the current waveforms in that experiment are similar to those that occur in real operation. The results obtained show that the resistance of the stator winding winding depends on the amplitude and frequency of current pulsations, while inductance is practically independent of these quantities. The generator idle test determined the electromotive force constant, which differs from the nominal value by approximately 5%. For the purpose of experimental verification of estimation results, a laboratory facility was built. All control functions and the estimation algorithm are implemented using a DSP, type TMS320C50. Thanks to the phase symmetry of the stator winding, the matrix equations of the PKF were simplified, which significantly simplified the estimation program in the DSP and shortened its calculation time. In stationary modes of operation, the results were experimentally checked at different speeds and loads. It was shown that the estimation results are better at higher speeds and with a loaded engine. The results were experimentally verified in dynamic conditions with a sudden change in speed reference and shock load. These results are practically equal to those in the stationary state due to the relatively large inertia constant. The possibility of simultaneous estimation of state variables and resistance of the stator winding was tested experimentally. In contrast to the simulation results, it was determined that the stator resistance cannot be estimated using this method. Finally, special attention should be paid to filtering the estimated speed, and additional delay due to the application of PKF should be taken into account when synthesizing the speed control circuit. The procedure for determining the time constant of the PKF is presented. The use of the estimated speed as a feedback signal has been experimentally verified, whereby satisfactory indicators of the quality of regulation have been obtained. The accuracy of maintaining the stationary speed (around the reference value) in the amount of ±1% of the nominal speed has been obtained at all loads and at all speeds greater than 5% of the rated value.

Abstract: A numerical model for calculating the impulse characteristics of an earth electrode has been developed. The finite element technique is used in the model creation. The calculation is performed in the time domain, while the parameters of the earth electrode conductor segment are frequency dependent.

Abstract: Based on the obtained documentation, a laboratory model of a frequency converter for powering a synchronous motor with permanent magnet excitation was created. The basic components available for the realization of the model were: AMDC330 development board with ADSP2171 processor (manufacturer Analog Devices), PM 50 RSA 060 intelligent inverter module (manufacturer Mitsubishi), synchronous motor with rotor position sensor. The energy, control and measurement circuits necessary for the realization of the model were created, as well as the processor program for drive control, and in particular for determining the dq components of the motor current for the needs of vector control.

Abstract: Using the PSpice program, components of a DC electric motor drive (motor, diode bridge, thyristor bridge and DC converter) were simulated. For a DC drive powered by a thyristor rectifier, selected stationary and dynamic operating modes were simulated. The paper presents the method of creating models of individual power electronics components.

Abstract: A numerical algorithm for approximating the frequency-dependent characteristic admittance and a numerical algorithm for approximating the wave propagation function have been developed. The numerical models are based on the point collocation method and the least squares method.

Abstract: On selected examples, the calculation of propagation of the traveling wave in the system of conductors with concentrated and distributed parameters was performed, and the efficiency of the program based on the Bergeron method and the developed program based on the finite element method were compared.

Abstract: A numerical model for calculating the impulse impedance of a meshed earthing conductor has been developed. The basis of the model is a combination of the finite element method and the method of characteristics. It is assumed that the parameters of a single segment of the earthing conductor are constant, i.e. independent of time and frequency. For a single straight conductor, analytical and numerical results have been compared.

Abstract: Based on the finite element method, a mathematical model was created for calculating the current distribution in the busbar armor, and on calculation examples, it was investigated how the armor grounding method affects armor losses.

Abstract: A new accurate method for the calculation of touch voltage and step voltage based on Thevenin equivalent and network foot model was developed. In addition, the impact of adding a surface layer of asphalt or gravel on the contact and step stresses as well as the percentage error resulting from the reduction of the real soil to the equivalent two-layer soil model was investigated.

Abstract: In this paper, a mathematical model of a vector control system based on a chained rotor flow was created. The mathematical model of the PID controller and the methods of adjusting its parameters have been elaborated. A simulation of the regulated electric motor drive was carried out and the time responses of the drive variables at a sudden change in the motor torque reference were compared for the vector control systems of the asynchronous motor based on the chained stator and rotor currents.

Abstract: In the laboratory of electrical machine control, there is an electric motor drive with an asynchronous squirrel cage motor powered by a frequency converter with a PWM inverter and a measuring system based on the use of a PC with an A/D converter DAS-20 and current and voltage sensors of the LEM type. The work involves simulation and measurement of asynchronous motor variables.

Abstract: For the needs of the FESB electrical machinery laboratory, a model of an electric motor drive with an electronically commutated motor (ECM) was created. The model consists of a 1.5 kW ECM, a diode rectifier, a DC intermediate circuit and an inverter. The motor currents were measured using an LEM sensor and an A/D converter. The following adaptive circuits are required for digital drive control using a TMS 320C50 signal processor: a circuit for processing signals from an incremental encoder, a circuit for generating commutation signals and a timing circuit for generating control signals. The aforementioned circuits were created as part of the diploma thesis, and based on the given control algorithms, a program for controlling the ECM using the aforementioned signal processor was created.

Abstract: This paper presents the theoretical basis for the optimal calculation of the stationary current field of mesh earthing conductors of a high-voltage electrical installation. The core of the paper is represented by three originally developed mathematical and numerical models. In Chapter 2, a mathematical and numerical model for the interpretation of data measured by geoelectrical sounding methods using direct or low-frequency current is described. Based on the data measured for one sounding point, the soil is replaced by a multilayer model with uniform characteristics in the horizontal direction, where the total number of layers is chosen arbitrarily. The interpretation is fully automated, and can be performed by a direct procedure, an iterative procedure, or a combination thereof. The direct and iterative interpretation are based on the analysis of the transformed resistivity function, which is directly related to the characteristics of the multilayer soil model. The transformed resistivity function is calculated from the measured data on the basis of analytical integration with a previous numerical approximation of the Stefanescu kernel function by a linear combination of up to 16 exponential functions. Using the same expressions, the apparent resistivity function is also calculated from the characteristics of the given soil model. Automatic direct interpretation is performed in such a way that the characteristics of the soil model layers are determined gradually layer by layer based on the approximation of the first part of the transformed resistivity curve, calculated from the measured data, using the curve of the two-layer model. After the characteristics of a layer have been determined, using the Pekeris recursive expression, the considered uppermost layer in the reduced soil model is discarded. Automatic iterative interpretation is based on the comparison of the sampled values ​​of the transformed resistivity function of the model with the values ​​calculated from the measurements. With an arbitrarily chosen total number of layers, the optimal characteristics of the soil model are calculated using the least squares method. The resulting system of nonlinear equations is iteratively solved using a variant of the Marquardt method, which converges quickly and reliably. In combined automatic interpretation, the model characteristics calculated by the direct method are used as initial characteristics in the iterative interpretation procedure. In Chapter 3, a mathematical and numerical model for the calculation of mesh earth electrodes laid in a multilayer soil with uniform characteristics in the horizontal direction is described. The procedure is based on the integral formulation of the problem. The total number of layers of the soil model as well as the total number of metallically separated earth electrodes is completely arbitrary. A single earth electrode can extend through multiple layers. The earth electrode conductors are divided into segments, and the line current density and potential of a single segment are approximated by the mean potential method. The generality and efficiency of the calculation procedure is achieved thanks to the successful application of the numerical approximation of two kernel functions of the integral expression for the potential distribution within the boundaries of one layer, which is caused by the current of a point source. Each kernel function is approximated by a linear combination of 15 exponential functions. The algorithm for determining the unknown coefficients of the linear combination is maximally simplified by reducing it to the multiplication of a known constant pseudo-inverse matrix and sampled values ​​of the kernel function under consideration. This is followed by a simple analytical integration using the Lipschitz integral. From a point source to a segment of the earthing conductor, integration is performed using a line source, which is assumed to be located in the axis of the segment. This calculation procedure represents a major advance in the field of calculation of the stationary current field of mesh earthing conductors. Its use achieves results of a high degree of accuracy in a short calculation time. In Chapter 4, a mathematical and numerical model is described for the calculation of mesh earthing conductors placed in a complex soil model, which can well approximate extremely heterogeneous soil such as karst soil. The procedure is based on the application of the finite element technique to a combination of differential and integral formulation of the problem. The three-dimensional calculation area is divided, using the finite element technique, into a small number of huge (subparametric) finite and infinite elements. Within one finite element, there can be several conductors, even the entire network of a single earthing conductor. The total number of metallically separated earthing conductors is completely arbitrary. The earthing conductors are divided into segments, while the approximation of the line current density and the potential of the segment is carried out by the mean potential method. The potential approximation function is built separately for each finite or infinite element. The combined procedure for calculating the earthing conductor is feasible on a personal computer with at least 16 Mb of RAM memory. Real examples of calculations can be performed in a relatively short computational time. Given the universality of numerical methods, all developed numerical procedures can be successfully applied in the research and solution of a number of problems in various branches of technology. Of particular importance are: an original way of solving the problem of a mesh source in a multilayer medium, an original way of solving the problem of a mesh source in a highly heterogeneous medium, and an effective combination of two different approaches in the finite element technique. Given the universality of numerical methods, all developed numerical procedures can be successfully applied in the research and solution of a number of problems in various branches of technology. Of particular importance are: an original way of solving the problem of a mesh source in a multilayer medium, an original way of solving the problem of a mesh source in a highly heterogeneous medium, and an effective combination of two different approaches in the finite element technique.

Abstract: Mode of action of TCR. Mathematical model of the compensation system formed by a TCR and a parallel filter on a three-phase network. Simulation of the occurrence of load changes in the node, and analysis of the current and voltage situation in the plant.

Abstract: The first chapter of the thesis describes the basic features of the finite difference method and the finite element method. The second chapter provides the theoretical basis of the finite element method. The third chapter elaborates four variants of the finite element method. In the fourth chapter, the finite element method is used for the numerical calculation of a 3D static current field. In the fifth chapter, the finite element method is used to model the static current field of a circular plate earth electrode placed on the surface of a heterogeneous soil. For a homogeneous soil, the results of the numerical calculation are compared with the analytical results.

Abstract: The goal of the final thesis was to automate the calculation of the node potential method using a program written in Python. AC circuits were used and, in this case, complex numbers that had to be included in the program were used. The second chapter describes the node potential method. The formulas show what is needed to calculate it. The third chapter covers the history of the Python programming language. After that, some features of Python are shown with a visual display using tables. The NumPy library, which was the basis of the program itself, is also mentioned. The fourth chapter presents examples that describe the entire program. The first example describes the entire program code in detail. The examples show how the program is able to solve circuits with and without a current source.

Abstract: The task of the final thesis was to model complex resistor-capacitor circuits in Simulink and to analyze the transient phenomena of capacitor charging that occur when the electrical circuit is connected to a DC source, as well as the stationary states when the capacitors are charged. The introductory chapter explains the task of the final thesis and its goals and the methods used to solve the task. The second chapter provides a definition of MATLAB and its possible applications. Simulink, a MATLAB software package used to model and analyze electrical circuits, is defined. Instructions for entering data and their description are provided for the Simulink block library Simscape and its components used in modeling. The third chapter analyzes each example separately. For each electrical diagram, the values ​​and arrangement of elements and a diagram image are given. The steps describe in detail the modeling of diagrams in Simulink and the analysis of capacitor charging and stationary values ​​of current and voltage when the capacitors are charged.

Abstract: The task of the final thesis was to describe the most common procedures for protecting photovoltaic systems with an emphasis on protection against lightning strikes. Due to their dimensions (kW/m2) and installation location, photovoltaic systems are almost always exposed to lightning strikes. This is an unfavorable condition because photovoltaic systems contain sensitive electronics (inverters), which require the introduction of some form of protection against lightning strikes and surges. The second chapter of the final thesis describes the procedure for the importance of implementing lightning strike protection, in two basic categories: when a photovoltaic system is installed on a building that is protected by a lightning protection system and when it is installed on a building that does not have a lightning protection system. Pictures are shown of the method of implementing protection when the facility already has lightning protection installed and it is explained when a type 1 or type 2 arrester is used. The second part shows the concept of surge protection on a building without external lightning protection when the separation distance is respected and when this distance is not respected, and tables are provided for the selection of SPDs depending on where we want to install the protection and depending on what kind of grounding system we are using this protection for. The third chapter deals with the case of lightning protection and surge protection in the case of solar power plants. The procedure for equalizing lightning potentials is described and tables for the selection of surge protective devices are provided. The concept of protection for collecting and evaluating data is also presented, which is very important because it allows the operator to identify and eliminate faults in a timely manner.

Abstract: This thesis analyzes the data sets from charging stations from different locations, some of them are public, i.e. availabe to everyone to use, while some of them are busnesslike, i.o. available only to employees. The distribution by arrival time, by required energy and distribution by idle and charging time were analyzed, all with the aim of finding the utilization rates of charging stations.

Abstract: The final paper describes the basic parts of solar power plants (SP), the method of connection to the power grid, the basic structure of the costs of building solar power plants, and the possibilities of modeling and analyzing the cost-effectiveness of investments in the SAM NREL program package. The basic parts describe the photovoltaic cell, photovoltaic module and DC-AC inverter. This final paper also describes the basic economic parameters used for profitability analysis and the basic cost structure of solar power plant construction. An analysis of the profitability of the investment in the program package SAM NREL was also presented, which offers us the possibility of modeling the system and, with the input of certain parameters, to obtain output data that will give the calculation of the invested and obtained money with the project profitability.

Abstract: This paper deals with primary types and classifications of energy storage systems. Even though there are various advanced solutions to this question this paper will firstly examine the most frequently used ones. In addition to descriptions of present-day systems the visual representation of them i salso shown. Since every system of storage has its own benefits and flaws it is necessary to elaborately analyze the systems in order to propose the appropriate one. Furthermore, this paper deals with the influence of the energy storage systems on the power grid in ways of its voltage and frequency stability in order to find out how to have more favorable conditions of the grid in relation to such systems. Ultimately the analysis of profitability and costs of energy storage system infrastructure is shown.

Abstract: The final paper briefly describes hydroelectric power plants, their applications and divisions, and their impact on the costs of produced units in the EES and on the electricity market. The second chapter describes various divisions of hydroelectric power plants. The most important division is according to the method of water use, i.e. flow regulation. According to this division, hydroelectric power plants are divided into: storage, run-of-river, and reversible. The parts of a hydroelectric power plant are also described and hydroelectric power plants in the Republic of Croatia are listed. The third chapter describes the characteristics of reversible hydroelectric power plants and their operating mode, which allows for the storage of energy during low energy prices and the use of that same energy during high energy prices. In the Republic of Croatia, we have two reversible hydroelectric power plants: Velebit and Lepenica. The fourth chapter describes the standardized operations on electricity exchanges in the Republic of Croatia and Europe, including standardized contracts traded on the exchange, methods of calculation, payments, and disbursements. Chapter 5 compares day-ahead energy prices for the UK market as well as prices for ancillary services for upward and downward regulation for the S3 Nordpool area from 2019, which we consider to be the year before the COVID-19 crisis, to 2021, which we consider to be the year of recovery from the COVID-19 crisis.

Abstract: The task of the final thesis was to review the most commonly used methods for testing electrical installations with an emphasis on the measurement procedure. Measurements are mainly carried out on installed equipment and in real conditions. Using the equipment and knowing the procedure requires certain skills of the measurer as well as compliance with all safety regulations. The second chapter of the final thesis describes the procedure for testing the continuity and resistance of conductors for potential equalization. Data on the minimum conductor cross-section and maximum length before exceeding the limit values ​​are presented. The second part describes the procedure for using metal elements for potential equalization, and the procedure for measuring resistance is presented. The third chapter discusses the procedure for testing insulation resistance. The procedure for testing insulation resistance for group and individual testing is presented. The procedure for measuring insulation resistance for a three-phase system is also presented, and data on the test voltage and the minimum permitted resistances obtained are presented. The fourth chapter gives the differences between TT, TNS and TNCS systems and shows the path of the earth fault current in the event of a fault on a consumer. The method for measuring the impedance of the fault loop is presented together with the connection of the measuring device. Chapter 5 presents the procedures for testing circuit breakers. The basic classifications, operating principles, advantages and disadvantages of circuit breakers are presented. The testing procedure for ELCB is not presented because it is being replaced by newer solutions, but the procedure for testing RCD switches using a device for testing the speed of switch response is presented.

Abstract: The final paper lists the laws that link fire protection and building construction. Parts that closely link the two areas are extracted from individual laws. By explaining the causes of fire and how to prevent its spread, an example of a fire alarm system in a shop and a coffee bar is given at the end as an example of the previously mentioned theory. The mentioned laws are found in the second chapter, where the topic they deal with and what they are divided into are stated. The most important parts related to the topic are commented on or quoted. The second chapter lists some of the possible causes of electrical fires that are related to device malfunction or user negligence. One way in which temperature changes in equipment can be monitored in larger plants is by using IR cameras, the use and application of which are explained in the fourth chapter. The fifth chapter is closely related to firefighting and thus includes measures of active and passive fire protection. The need for protection is explained as well as the method of its implementation. The sixth chapter shows the power of fire that destroys everything in its path and takes human lives with it. Examples are shown here where a harmless situation turns into a disaster. In order to cover the entire topic of the final thesis, from standards to the implementation of fire protection, the seventh chapter presents an example of a fire alarm system in a store.

Abstract: This paper describes the possibilities of using the sun and solar radiation to obtain electricity and what types of technology are used for this. Ways of battery storage of electricity with emphasis on lithium-ion systems are described, and then the possibilities of the SAM software package for modeling solar power plants and battery warehouses are described. Then, a model of a solar power plant and a battery warehouse was made in it, and data on electricity production, financial profitability and cash flow for such a project were presented.

Abstract: The purpose of this paper was to formulate and optimize a sustainable and cost-effective micro grid solution based on a solar photovoltaic grid and a diesel generator for the supply of electricity to populated areas that do not have access to electricity and remote areas away from the main grid. The production of electricity from renewable energy sources is subsidized, which has led to greater application in distribution networks. Island photovoltaic systems have found their place in performing two important functions: providing power in areas without access to the public electricity grid and ensuring uninterruptible power supply in networked systems. Such systems are mostly installed in areas of Africa, Asia and South America where the public electricity network is poorly developed. Designing an island photovoltaic system requires a good knowledge of photovoltaic technology, power electronics and the climatic specifics of the location itself. The main problem in optimizing island photovoltaic systems in our geographical area is the very large differences in irradiation between the winter and summer months. This makes the whole project more expensive because much more investment is needed in photovoltaic modules, which are the most expensive part of the system. Experience and analysis so far show that it is still best to use a hybrid photovoltaic system or a combination of photovoltaic modules and diesel generators because we get complete independence of the system, optimal use of diesel generators, batteries and reduce the total initial investment. The program used to optimize this system has changes in load and power consumption per hour, which gives it great precision for calculating data, and more accurate optimization.

Abstract: The first part of the final paper describes the idea and operation of the device for recording the current-voltage characteristic. At the beginning of the work, the principle of operation and the very idea of the device are described. The following sections describe its implementation in practice and the development of the device through the first generation of IVS1 until the final minimized and practically realized IVS2. In the second part of the final paper, the operation of the photovoltaic cell/module is described. The important characteristic points when performing measurements and drawing the current-voltage curve are explained. The influencce of incident angle of light on the photovoltaic module and its connection with the power given by the photovoltaic module, are also described. The third part of the final paper describes the operation of IVS2, the necessary components for the practical design of the device. The manual generation of current and voltage characteristics, the basics of IVS1 operation and the advantages of improved IVS2 compared to the previous version are described. The fourth part describes the practical implementation of IVS2. In this final paper we made a version of the device for recording the characteristics of the photovoltaic module with the help of a printed board and an electromagnetic relay. In the fifth part, measurements were performed and shown using the device. The characteristics for different lighting conditions were recorded and attached. The measurement conditions are described ,and the components used are listed.

Abstract: This final thesis describes the principle of electric chargers for electric vehicles. The types, charging modes and the costs of the charging stations are described. It also describes in detail how to charge the batteries of an electric vehicle, through the network in combination with renewable energy sources. The types of modules and chargers, their advantages and disadvantages, are also described. At the end of the paper, the advantages, and disadvantages of switching from diesel and gasoline engines to electric motors are listed as well as and the general impact of the connection of electric vehicles to the electricity network

Abstract: Photovoltaic power plants (PPPs) or solar power plants are renewable energy sources that are gaining increasing importance today. Solar power plants transfer the generated electricity to the power system, enabling direct conversion of solar energy into electricity. The term thermal application refers to the direct use of solar energy for heating water, heating buildings or cooling a building. A more complex way of using solar energy (as opposed to passive solutions) is achieved by using thermal collectors. Photovoltaic cells are used as an independent or additional source of energy. As for the photovoltaic system, it can be connected to the power grid in two ways: by connecting to the power grid via a home installation or by directly connecting to the power grid. The disadvantages that arise when using solar energy are the inability to adequately store larger amounts of energy, there are oscillations in radiation intensity during the day and year, dependence on climatic conditions, lack of security of supply, radiation intensity does not match consumer demands, all in all, the production of electricity from solar sources is still not economical enough, therefore additional incentives are needed. Solar energy could become the main carrier of environmentally sustainable energy development in the near future as a highly acceptable renewable energy source. This is becoming the main reason for increased research into new procedures and processes for converting solar energy into electrical and thermal energy. Every energy plant, including solar power plants, changes the picture of the natural environment to a certain extent. In solar power plants, there is no combustion process, emissions of harmful substances, harmful impacts on air and water quality, soil degradation and noise impacts on the environment, so that if legal obligations are adhered to, the negative impacts of solar power plants will be minimal or negligible.

Abstract: The task of the final work was to model the power system of the ship, which includes the electric propulsion system, in the Simulink environment of the MATLAB software package. The created simulation model of the ship’s power system should, in addition to the electric propulsion system, contain elements that model the production, transmission and consumption of electricity on the ship. Finally, on the basis of the selected literature, the main and auxiliary parts of the created simulation model of the ship’s power system had to be described. In the second chapter of the final thesis, the production of electricity on the ship is described. The basic and auxiliary sources of electricity and the basic principles of the ship’s power plant are mentioned. Basic sources of electrical energy on board are covered in detail. Auxiliary sources of electricity did not need to be processed in detail, because they are not in the simulation model. In the third chapter of the final thesis, the most significant differences between the marine and land power systems are given, and the main and other elements of the ship’s electrical network are listed. Direct current and alternating current distribution systems are also mentioned. The alternating current distribution system was treated in more detail than the direct current distribution system, because it was used in the modeled simulation. In the fourth chapter of the final paper, four basic groups of electrical energy consumers on the ship are listed. Of the four mentioned groups of consumables, electric motor drives and electric propulsion are covered in more detail. In the case of electric propulsion, the description of propulsion with electric transmission was detailed, because it is used in the simulation. The fifth chapter of the final paper describes the main and auxiliary elements of the simulation. Then a description of the simulation as a whole is given, as well as the order of events during the simulation. At the end, the results of the simulation during operation are presented with appropriate comments on the obtained values.

Abstract: In this thesis, small hydropower plants are described as a plant in which the potential energy of water is converted into the kinetic energy of its flow, then into the mechanical energy of rotation of the turbine shaft and finally into electrical energy in a synchronous generator. The second chapter describes the properties and characteristics of the hydropower plant, while the third chapter describes the components of the hydropower plant. A small hydropower plant consists of all plants and buildings from water supply and drainage, plants for the production of electricity and transformation to a level suitable for the final consumer. The fourth chapter describes the method of calculating the hydro potential and determining the possible production of electricity from a small hydropower plant. While the sixth and seventh chapters explain the economic viability of SHPPs and the consequences of SHPP connection to the distribution network in the context of power flows, loads, voltage quality, re-establishment of drive after failure, parallel drive with distribution network, power reliability and frequency change in the network. In the final, eighth chapter, testing and simulation of conformity of production modules is explained.

Abstract: The final paper describes compact medium voltage switchgear blocks, their classification, design and configuration in a way that complies with IEC standards. The second chapter discusses the classification of switchgear blocks, standards that indicate the design of switchgear blocks, the impact of SF4 gas on the environment and safety measures. The busbar compartment and the compartment for housing connections are separated from the switchgear compartment. Each switchgear block consists of a compartment in which the primary elements are located and the variants in which they can be designed, as described in the third chapter. The fourth chapter describes the configuration of switchgear blocks, which consists of individual fields as a separate unit with the examples given. The remaining chapters present in detail the designs of switchgear blocks from different manufacturers such as BVK, RM6, SM6, SafePlus/SafeRing, with regard to the installation location, their construction, insulation types and characteristics (arc extinguishing, control method, etc.) together with the nominal data for which they are designed.

Abstract: This final paper describes the differential protection of power transformers and its application in the transformer protection system. The basic requirements for differential protection are given, so that it can function as such in the system in the event of a fault or dangerous condition in the power system, and without interrupting the power supply to the end consumer, if possible. In the second chapter, in order to better understand the importance of the power transformer in the system, a basic description of the transformer is given. The classification of transformers, types of transformers are briefly described, and a characteristic diagram of the transformer with the corresponding markings is given. In the third chapter, dangerous operating conditions of the power system and types of failures of the power system are described, which in any case represent a danger to the safe functioning of the transformer. Both the power system and the transformer are exposed to various atmospheric discharges, mechanical damage, insulation damage, etc. on a daily basis. In the fourth and fifth chapters, the importance of differential protection of power transformers is described. The specifics of power transformer differential protection, static and numerical differential relays, and when and why stabilized differential protection is used are briefly presented. In the fifth chapter, multifunctional relays from Končar, ABB and Siemens are described and some of their possible functions are shown.

Abstract: The introductory part explains which electrical properties are contained in electric power lines. Also, the advantage of overhead in relation to underground lines was explained, as well the most commonly used types of conductors in transmission lines. The third chapter describes the resistance, and its change with increasing temperature. The fourth and fifth chapters describe the inductance and capacity of power lines, and their calculation in relation to types of line, the number of bundle conductors, and whether the line is transposed or not. The method of mean geometric distances used to calculate capacitance and inductance is also described. At the end of the work, typical examples are shown for 110-kV, 220-kV, and 440-kV lines used in Republic of Croatia, and their solutions in the Matlab.

Abstract: The task of this final paper is to conduct a cost-effectiveness analysis of the construction of a solar power plant on a selected example, taking into account the new Act on Renewable Energy Sources and High-efficiency Cogeneration. The first part describes the technical potential of solar energy required for the operation of photovoltaic systems and the occurrence of the photovoltaic effect that is the basis for the production of solar energy. Then, photovoltaic systems are described, from the history of solar cells, through their types to the way they can be connected to the electricity grid, and an overview of technologies on which the future of solar energy use should be based is given. The second part analyzes the economic profitability of building a solar power plant using a model made in Excel that takes into account the insolation of the location, the possibility of tilting the module, the characteristics of the module and household electricity consumption to ensure maximum return on investment.

Abstract: The aim of this work is to explain the optimal voltage regulation in the distribution network through the theoretical and practical part. The introduction lists the four main units of the power system and its main task as well as the two basic types of distribution networks. The second chapter lists the basic equations for the voltage drop along the circuit and the ways in which the voltage drop along the circuit can be reduced. The third chapter describes the voltage drop allocation, the principle of the load flow model and the problems and voltage reduction including the solution of these problems. The fourth chapter describes the principle of operation of the regulator as well as three types of compensation: line-drop compensation, load-center and voltage-spread compensation. Chapters five and six describe the methods for parallel operation of regulators, bus regulation settings and line loss and voltage drop relationships. In the practical part of the work, the optimal voltage regulation is shown using the DIgSILENT PowerFactory program, and the voltage profiles before and after the optimization are compared.

Abstract: One of the most important parts in the electric power system is the distribution system as it connects transmission networks with their end users – customers. Due to constant technological and industrial development there has been a significant increase in electricity demand. Therefore, the distribution systems have become more complex which requires frequent improvements in the reliability of distribution systems. Some of the main distribution system problems include: the minimization of total losses in the distribution network, equalization of voltage profiles along MV terminals, equalization of load per terminals and increasing reliability of power supply. To minimize these problems it is essential to plan the structure of the distribution network. There have been developed various reconfiguration methods aiming to reduce overall system losses, equalize voltage profiles, load, and increase reliability. Distribution system reconfiguration consists of changing the distribution network topology in order to find the most optimal topology. This paper covers optimization methods, the proposed model of SN 10 kV network for the real area processed with DigSilent Powerfactory software package and complete analysis of power flows, voltage conditions, loads and power reliability for the existing network switching condition. By using the DM topology optimization module, the optimal network switching condition was determined regarding a certain target function. The obtained results are presented and thoroughly analyzed.

Abstract: In this thesis, in the first part we discussed about different charger topologies for electrical vehicle. We describe three levels of chargers and compare them. Also, we mention SAE charge standard and battery technology which is most important part of electric vehicles and charge stations which have built-in batteries. In second part of this final paper we describe and compare impact of connecting large charging stations on the electrical grid with device for smart charge and without it. At the end of this final paper we talk about ancillary services to the electrical grid provided by large charging stations.

Abstract: Low-voltage networks are networks with a nominal voltage lower than 1 kV and without exception belong to distribution networks. Low-voltage networks are the most widespread part of the power system. There is almost no settlement, village or hamlet in the developed part of the world that does not have an electric grid. The task of low-voltage networks is to provide all consumers connected to them with a high-quality supply of electricity and to ensure the protection of consumers from direct and indirect contact with live devices, especially in the event of malfunctions. In this final paper, a detailed analysis of the calculation of the low-voltage electrical network TS 20(10)/0.4 kV Marusinac 3 is described and carried out using the WINDis software package. The possibilities of the WINDis program package are briefly described in the second chapter. In the third and fourth chapters, the current and planned state of the electrical network is presented. Formulas are given for calculating short-circuit currents, which are necessary for the correct selection of fuses that will protect the network from overload. In the last chapter, a detailed analysis of the low-voltage network TS 20(10)/0.4 kV Marusinac 3 was carried out in the program package WINDis for each extract, while adhering to the prescribed electric power norms and prescribed standards.

Abstract: This work presents smart lighting and describes its parts and the benefits of installing it. After that, a light-technical calculation was made for one office where smart lighting is planned to be installed. The practical equipment testing was carried out in the laboratory conditions of the company LEDeno Doba d.o.o. All equipment that will be installed later is tested in the laboratory. The paper also describes communicate for DALI devices used for smart lighting systems. Three control modes are described: manual, automatic and using smart devices. After the connection, in practical part selected equipment was tested with some external signals and interference and the test results showed that the equipment was of high quality and the system worked without problems.

Abstract: The main objective of this document was to realize the system a practical model of the system for active monitoring the position of light based on the Arduino platform, and to continuously monitor its work. Multiple photovoltaic panels can be connected to the selected controller, but all tests and measurements have been performed on a single panel. This document describes in detail all the electronic components that were required to create the model. The communication between the computer and the controller of the photovoltaic panel is described. An application has been created that allows the user to manually and automatically control the photovoltaic panel. It also describes the processing of an analog signal that needed to be averaged to allow the controller to control the rotation angle correctly.

Abstract: The introductory part of this work describes the basic principles of wind energy conversion as well as electricity production from wind turbines. It contains a list and overview of internal and external parts of wind turbines. In addition to this different ways of connecting wind power plant to the electricity grid are described in addition to technical conditions which must be satisfied. Detail technical data related to the wind turbines; transformers and medium voltage cables used in the internal cable network is described for wind power plant „Krš - Pađene“.The cable routes and characteristic cross sections of cable ducts which lead to wind turbine substations and main supply substation are given. Depending on the number of connected wind turbines per feeder; the length of the feeder and the cable type; the calculation of the current sizing of the cables is described. For defined internal cable network detail power flow calculation is conducted using MATPOWER software package. The calculation uses the input data related to cable lines; transformers and buses electric parameters and produces results related to power flows; power cable line loading level; voltage increase and active power losses in the internal cable network.

Abstract: The introductory section explains the reasons for the need for voltage regulation in the distribution network so that all consumers have a fairly equal amount of voltage of the nominal amount. The second chapter describes the voltage regulation procedures in general, we touched on the back-up power supply of adjacent MN networks to provide additional protection in the event of a power failure of a substation. Also in the second chapter we have seen some basic voltage regulation schemes of main substations. After introducing the general voltage control modes in Chapter 3, the control modes are explained in more detail, such as automatic control of the main substation HV or LV bus, voltage compensation, and some analyzes of voltage regulation using additional reactive power injection from the HV network to the MN network. In the practical part, the data were analyzed after applying the method of changing the transformer switch. In addition to the above method, the method of simultaneous use of the Booster transformer and the method of changing the transformer switches were used. Both methods proved to be positive and led to an improvement in voltage conditions, as can be seen from the graphical representations. Although both methods are effective, by installing Booster transformers we achieve better voltage opportunities on terminals that have longer lengths and more consumers.

Abstract: This paper begins by generally describing hydro power plants and their parts, as well as mentioning the biggest hydro power plants in the world. This is followed by a description of small hydro power plants, their construction and the two types of small hydro developments. In addition, we look at some of the formulas required for calculation that takes place at the end of the paper. Before the very calculation, we have a detailed description of every type of turbine we used, as well as tables of formulas for flow and efficiency of each turbine. Using the mentioned tables and calculating these formulas, we obtained an efficiency curve for each turbine. Furthermore, the terms for total production of energy on a daily, monthly and yearly basis are written down. By calculating the terms at the very end of the paper, we obtained the tables for total production. These are substantiated with corresponding diagram of production of energy on a monthly basis.

Abstract: The topic of this final thesis was the description of relay protection. Through the work, we have shown how relay protection, with its development over the last half century, has greatly contributed to the safety and stability of our power system. We have presented its development through all three generations, and explained their disadvantages and advantages in more detail. Furthermore, the types of basic relays are described and their functioning is explained. Having familiarized ourselves with the most important types of protection and their principles of operation, we come to numerical relays, which are represented in the paper by the described Siemens SIPROTEC 7SJ82. We find its application in the renovation of the 110/35 kV Meterize substation, where the relay itself was introduced as the main protection of the plant by replacing the 35 kV plant. By presenting the plant and its technical data, we see what this relay actually protects. It contains a huge variety of protection, and is parameterized by the user to those protections that it needs. This is processed by the DIGSI 5 engineering package, which was produced to make the user’s job easier, and its capabilities are also extensive. The Omicron CMC 256 relay test device, its main parts, and its characteristics are described.

Abstract: This final paper describes the spectral measurement of noise in a communication node. The physical foundations of noise as a phenomenon are given, the physiological effects of noise in terms of human health are described, and noise measurement techniques are described. Measurement problems are elaborated and instrumentation is described. The practical part of the paper includes examples of measurements on typical noise sources in an apartment and spectral measurements in 3 communication nodes (server rooms) at the Faculty. The concluding part comments on noise levels, spectra, and possible impact on human health.

Abstract: This final paper deals with the topic of electromagnetic radiation from extremely low frequency fields, more precisely from 10 kV, 110 kV and 400 kV power lines, with the aim of proving that the radiation values ​​are below the permissible limits. Radiation is the phenomenon of energy spreading in the form of waves or particles (ionizing radiation) or in the form of electric and magnetic fields (non-ionizing radiation). Ionizing radiation penetrates the interior of the human body and directly affects cells, while non-ionizing radiation only affects the surface of the skin. Electromagnetic radiation is a form of non-ionizing radiation. With regard to frequency or wavelength, EM radiation is divided into a spectrum consisting of gamma radiation, X-rays, UV rays, IR radiation, the visible spectrum and radio waves. By concentrating on extremely low frequency fields (50 Hz), more precisely household appliances, power plants and power lines, which are the main topic of this paper, we take into account the fact that electric and magnetic fields can be considered separately. Below the power line, the electric field is of constant value as long as the lines are energized, while the magnetic field varies depending on the load current. From Maxwell’s equations, which are the foundations of theoretical electrical engineering, formulas are derived that describe how the values ​​of the electric and magnetic fields depend inversely on the distance from the power line, i.e. that the field decreases with distance from the power line. In the Republic of Croatia, regulations have been adopted that define the limit values ​​of electromagnetic radiation, in the categories for professional exposure, the general population and particularly sensitive areas, which are, in turn, increasingly strict. Measurements in residential areas have shown that in some devices such as vacuum cleaners and stoves, the magnetic field (electric motor, induction) prevails, while in DVB-T the electric field prevails. By measuring the electric and magnetic fields in three spatial axes, results were obtained that show that the radiation from power lines 10 kV, 110 kV and 400 kV is far below the prescribed limit values. Therefore, all misconceptions about the harmfulness of power lines have been refuted.

Abstract: In this final thesis, the second chapter is dedicated to the design and characteristics of a step-down DC-DC converter without galvanic isolation. After a brief explanation of the influence of parasitic components of the LC circuit on the operation of the converter, in the third chapter, the values ​​of parasitic resistances of the capacitor and the choke are determined using experimental methods and calculations. The fourth chapter presents a simulation model in which the values ​​of parasitic resistances that were experimentally determined in the third chapter are used. The fifth chapter analyzes the waveforms of the simulation model. In the first part, the parasitic resistances are set to zero, in the second part, the measured value is added to the parasitic resistance of the inductance, and in the third part of the fifth chapter, the parasitic resistances of both the choke and the capacitor are included. The corresponding waveforms are analyzed and compared in order to determine the influence of parasitic resistances on the operation of the converter under consideration.

Abstract: This final paper deals with the calculation of losses in a three-phase converter based on catalog data of commercial IGBT modules. The losses were determined using the MATLAB Simulink software package. The chapters describe power electronics converters, as well as the algorithm for calculating losses, which is based on hysteresis pulse-width modulation. Through simulations in the MATLAB Simulink software package, IGBT module losses were tested for different amounts of phase current, DC voltage and switching frequency. The simulation results are presented in graphical diagrams and all results are commented on.

Abstract: This paper explains how parasitic resistances of the choke and capacitor affect the operation of a DC-to-DC boost converter. The second chapter explains the basic principle of operation of a DC-to-DC boost converter without parasitic resistances, and describes the operating modes in which the converter can operate (continuous and discontinuous operation). The third chapter theoretically explains the influence of parasitic resistances on the operation of the converter, as well as the principle of experimentally determining the actual parasitic resistances of the capacitor and choke. Then, the fourth chapter discusses the method of applying a simulation model for the purpose of determining the influence of parasitic resistances of the choke and capacitor. In the fifth chapter, we have tried to clearly demonstrate the influence of parasitic resistances on the operation of the converter, using comments and images of the voltage and current waveforms of individual converter components, for three cases. In the first case, we explained how the converter would operate without parasitic resistances. In the second, we included the parasitic resistance of the choke and tried to compare it with the first case. In the third case, we took into account the parasitic resistances of the choke and capacitor and explained how these two components combined affect the operation of the converter.

Abstract: This paper describes the use of Arduino microcontrollers, stepper motors and photoresistors, which are connected with the help of software into a functional unit for monitoring light sources. The task was realized in several ways with the help of a PC with a graphical interface in automatic mode, manual mode, and in fully autonomous mode. The model is assembled into a functional unit that can be applied to static and moving objects.

Abstract: This paper describes microgrids with a large proportion of renewable sources, and electric vehicles as consumers and sources of electricity. The aim of the work was to analyze the influence of electric vehicles on the operating conditions of the microgrid. In order to carry out such an analysis, basic knowledge about the principle of operation of microgrids, renewable energy sources and electric vehicles is required, which is covered in the first part of the paper. After this knowledge was adopted, a microgrid model was designed in the MATLAB software package, in which all the previously mentioned elements essential for a properly conducted analysis were used. By simulating the operation of the microgrid without, and then with the influence of the V2G regime, different results of electricity production and consumption in the microgrid were obtained. By observing the frequency deviations in both cases, the conclusion was reached that the use of the V2G regime must be carried out within certain limits of the integration of electric vehicles in order to achieve the best possible regulation of the operating conditions of the network.

Abstract: In the first chapter, an overview of the structure of the distribution system, its components, and the role of the distribution system in the larger picture of the power system is given. Then, in the following text, terms related to the quality of electricity, factors that provide insight into the quality of delivered energy and reliability of delivery are explained. Basic modeling of system components and their behavior as they age are also explained. Before the elaboration of some more complex analyzes and simulations of system behavior, the basic terms related to these simulations and analyzes are explained in order to enable a clear understanding, and the frameworks and principles of modern methods and analysis of distribution systems are given.

Abstract: The theoretical part of this final paper describes distribution networks, their characteristics and specificities. Special emphasis is placed on low-voltage distribution networks, which, in addition to phase conductors, also have a neutral conductor, and earth as a return conductor. In this paper, the Backward-Forward algorithm was used for calculating the power flows of the low-voltage network, which is based on Kirchhoff’s laws and the calculation of voltage drops on all busbars of the network. This algorithm is convenient to use because it converges even in cases of large R/X ratios that are characteristic of distribution networks. In the experimental part, this algorithm was implemented in the Python program package. The BF algorithm was used to calculate the power flows of the radial distribution network of 9 buses and a network of 906 buses. It is shown that the developed algorithm is a powerful tool with which we can calculate the power flows of an arbitrary distribution network. To verify the accuracy, the results were compared with the OpenDSS software package and the accuracy was confirmed numerically using a very low percentage error of the order of 0.0001%.

Abstract: A solar cell is an electronic device designed to convert solar energy into electricity and represents the technology of the future. Since silicon currently dominates the world market, this paper considers basic measurements on monocrystalline and polycrystalline silicon panels. Using a temperature chamber and artificial sunlight, module efficiency measurements were made in laboratory conditions. The same was done in real conditions for mFNE. Based on the results, conclusions were made about the optimal operating mode of the solar panel.

Abstract: This paper describes the basic elements of the electrical installation of a passenger car, with special emphasis on signals on the CAN bus. The historical development of electronics inside the vehicle is briefly described, as well as the form of signals and message topology, and the medium used for their transmission. Special attention is given to the types of sensors with characteristic examples for electrical and non-electrical signals. The characteristics of the Raspberry Pi development platform and its applications in electronic installations are described, as well as the software development steps, characteristics of the developed version and possible upgrades. The results obtained by connecting the Raspberry Pi microcomputer to the CAN bus are processed in such a way that CAN messages are filtered based on addresses and contents within the data fields, and are stored in variables that are later called in the graphical interface. Finally, the result is a control panel for displaying information with the minimum number of wires required for creating an electrical installation.

Abstract: This paper describes the techniques for testing the winding resistance of a synchronous generator with auxiliary Diesel power supply. After a short theoretical introduction describing the principle of a synchronous machine, an overview of the measurement methods is given (indirect measurement using the U-I method and direct four-wire measurement). The central part of the paper is practical measurements of 2 synchronous generators, analysis of the results and conclusion on the correctness of the machine in the context of the amount of winding resistance.

Abstract: This final paper describes busbars, their role and application. Their operation under normal operating conditions and under short circuit conditions is analyzed. The second chapter presents the method of manufacturing busbars and the materials used in their manufacture. It also discusses the properties of aluminum and copper conductors and their alloys. The role of insulators in electrical installations and the method of their construction and installation is also described. In normal operation, the cross-section of busbars is selected according to the maximum current flowing through the most loaded part of the busbars. This current is determined by the thermal load. The negative effects of temperature increase and the selection of busbar cross-sections are described in the third chapter. The fourth chapter presents the thermal loads of busbars during a short circuit, the calculation of the required cross-sections and temperature increases. The negative effects of electric arcs and pipe expansion are also described. The last chapter presents the mechanical characteristics of busbars during a short circuit and the forces that destructively affect them. The stresses of busbars in their standard design are analyzed.

Abstract: This paper presents methods for calculating short-circuit currents according to the international standard IEC 60909. Short-circuit currents need to be known in order to plan further development of the power system, adjust relay protection, dimension electrical equipment and design earthing switches. The second chapter describes the characteristic short-circuit currents, and lists the types of typical short circuits such as single-phase, two-phase, three-phase short circuits and two-phase short circuits with simultaneous connection to earth. The consequences of a short circuit such as thermal and mechanical stresses and possible ways to prevent it are also listed. The third chapter describes in detail the methods for calculating short-circuit currents: the equivalent voltage source method and the symmetrical components method. In addition, the calculation of maximum and minimum short-circuit currents is described and the equivalent impedances of electrical elements required for calculating short-circuit currents are given.

Abstract: In this final paper, various designs of submarine cables, single-core and three-core, were analyzed and compared from a technical and economic perspective. Previously proven data was used throughout the analysis. The second chapter provides general data on cables. The third chapter discusses the analysis and comparison of various technical parameters of 110 kV submarine cables. The technical characteristics, i.e. the advantages/disadvantages of single-core and three-core cables - transmission power and losses, resistance to possible cable damage caused by passenger or fishing boats, were compared. The prices of single-core and three-core cables, laying prices, maintenance costs, cable transport prices from the factory to the laying site, coastal protection prices and finally a recapitulation of all costs are analyzed in the fourth chapter of this paper. The analysis conducted shows that the best solution for the given example is to select a submarine cable with a cross-section of 3x630 mm2 for the highest quality and most reliable power supply.

Abstract: This paper describes the tests of high-voltage switches and their connection with valid standards. The basic parts of the switch and their role in operation, as well as the general principle of operation, are mentioned. Valid standards that prescribe all tests and generally everything related to high-voltage switches are listed. The differences between domestic and international standards are explained. All methods of circuit breaker testing are listed according to importance and frequency. The results of the routine testing of the high-voltage 123 kV circuit breaker in TS Kraljevac were presented.

Abstract: This paper presents the basic construction and principle of operation of transformers for galvanic separation, as well as their application in medicine, where they represent one of the basic measures of protection against indirect contact. Transformers for galvanic separation meet all the criteria prescribed by the international standard IEC 60364-7-710. Special attention is paid to the detailed presentation of two basic types of transformers for galvanic isolation: ES710 and DS0107, as well as to all other equipment manufactured by Bender, which make up the protection system of the University Clinical Hospital Mostar.

Abstract: This paper presents international and domestic regulations related to standard voltages of electrical networks, types of overvoltages to which elements of electrical installations are exposed, and test voltages used for insulation testing. Overvoltages are defined, the classification of overvoltages is presented, the most common causes of their occurrence, and their basic characteristics. The most common cases are listed with respect to the locations of atmospheric overvoltages, as well as the ways in which switching overvoltages occur. Methods of generating test voltages are also described.

Abstract: In this paper, detailed guidelines are given and it is shown on a concrete example how to make the main project of home electrical installation - used norms and rules, presentation of protection measures, quality control program, calculation of selected electrical equipment as well as all necessary schemes and cost sheet.

Abstract: The student should describe the thermodynamic principles of heat transfer and state and describe the basic laws of thermal radiation. Furthermore, thermography should be described as a method of non-contact temperature measurement, with special emphasis on the difference between qualitative and quantitative thermography in the maintenance of power plants, as well as the components and operating principle of a thermal imaging camera. Finally, the acquired knowledge should be applied in the thermal imaging inspection of a solar power plant, processing of thermograms and recommendations for its maintenance.

Abstract: The student should describe the basic concepts of the grounding system, types of grounding electrodes and analytical expressions that enable the estimation of grounding resistance from knowledge of the grounding electrode geometry and specific soil resistance. Then, the methods of measuring grounding resistance and permissible values ​​according to the applicable legislation should be described. The acquired knowledge should be applied to measuring the grounding resistance of several 10/0, 4 kV/kV substations and conclusions should be drawn about the quality of grounding.

Abstract: The student should describe the characteristics of the central monitoring and control system at FESB. Special attention should be paid to the characteristics of sensors and actuators that can be monitored via CNUS in the context of controlling the lighting and heating, ventilation and air conditioning (HVAC) systems. In the practical part of the work, the programming of sensors/actuators should be described and the building parameterized for a given week should be set. In addition to the above, typical faults (alarms) detected by CNUS should be processed, as well as techniques for eliminating these faults. Furthermore, it is necessary to create weekly and monthly diagrams of air temperature and carbon dioxide concentration for given amphitheaters and use them to explain the parameterization of the building. In the remainder of the work, the CNUS should be simulated on the example of a family house by performing a series of process measurements that would be obtained with CNUS and, based on the results obtained, conclusions should be drawn regarding the condition of the house and the settings of the home’s thermotechnical systems.

Abstract: In this final paper, an idling test of an asynchronous motor powered by a frequency converter was performed, with the aim of determining the losses incurred. The second chapter discusses asynchronous motors in general and their basic characteristics, such as the principle of operation, the design of asynchronous motors, and the construction itself. The third chapter discusses frequency converters, with special emphasis on indirect frequency converters with a DC voltage intermediate circuit that was used in this experiment and sinusoidal PWM modulation that controls the commutator switches of this indirect converter. The fourth chapter deals with the description of the idling test of an asynchronous motor, i.e. what can be determined from the idling test, and the experimental determination of idling losses.

Abstract: This paper describes different types of stepper motors and their operating principles. Then, the disadvantages and application areas of stepper motors are listed as a conclusion to the theoretical part. Then, the relationship between the voltage at the output of the rectifier of the speed measuring element and the actual speed of the motor is experimentally determined. Thanks to the relationship between the frequencies of the fundamental harmonic and the pulsations, a passive RC filter is constructed to reduce these pulsations to an acceptable level. For 3 different filters, their disadvantages and advantages are given and described.

Abstract: In this final paper, the stator flux linkage of an unloaded induction motor is determined from the measured stator voltages and currents. First, a theoretical analysis of the design and operating principles of an induction motor is given. Within the theoretical part of this paper, a classical dynamic model of an induction motor is presented and the stator flux linkage equation is determined. This equation was used for the measurement results in the experimental part, in which the flux linkage was determined by simulation and using the phasor diagram of an unloaded induction motor. Finally, the two previously mentioned methods for determining the stator flux linkage are compared and an analysis of the obtained results is given.

Abstract: This paper outlines the monitoring system of the entire switchgear, while the monitoring system of high-voltage circuit breakers is described in detail. The measured quantities and the method of displaying the measured quantities (graphically, numerically) are listed. The external influence on the monitoring system of high-voltage circuit breakers and the methods of protecting the protected object (circuit breaker) are also described. The main characteristics and designs of the monitoring systems of high-voltage circuit breakers manufactured by Siemens, ABB and Končar are presented.

Abstract: This paper describes a mathematical model for calculating the magnetic flux density of a cable system, which can take into account any number and arrangement of single-core cable systems arranged in a triangular bundle or laid in a plane at any distance from each other. A matrix of reduction coefficients is used, which takes into account the complete electromagnetic coupling between the associated cable lines. The application of this model allows the calculation of the distribution of currents flowing through metal screens in a cable system, and then the magnetic flux density at arbitrarily selected points in the air, depending on the geometric arrangement and number of single-core cable systems, which is shown in the selected numerical example. In addition to the well-known factors that significantly affect the amount of magnetic flux density, such as the amount of current and the depth of laying, the results obtained also indicate a significant influence of the method of laying and arrangement of phase conductors, which can be used in the planning and design of new cable lines.

Abstract: In order to produce electricity from the energy of solar radiation, it is necessary to know certain parameters, the basic of which is the global solar irradiance on the horizontal surface. In order to achieve greater electricity production, solar panels are placed at a certain angle or actively follow the movement of the Sun. Calculations of the expected irradiance on solar panels depend on the model used to transform the measured global irradiance values ​​for the horizontal surface to the values ​​for the tilt of the panels. In this paper, the irradiance calculation of the panel under variable inclination was performed using the initial measured values ​​of the global solar irradiance on the horizontal surface. The first part of the paper describes basic terms related to the Sun and solar radiation, the geometric relationship between the Earth and the Sun, the influence of the atmosphere on radiation, and the components of solar radiation (direct, scattered, reflected). The second part of the paper describes the calculation of solar radiation and the application of that calculation for the city of Split. The Liu-Jordan model for south-facing surfaces was chosen for the calculation, and this model was extended by Klein to arbitrary surface orientation.

Abstract: This paper explains the concept of thermal imaging, a method that has recently been increasingly used in the maintenance of power plants. The second chapter contains basic concepts from heat and describes the thermodynamic foundations of heat transfer, among which thermal radiation is highlighted, which is of great importance in thermal imaging. The third chapter describes the parts of a thermal imaging camera, which represents the central object of a thermal imaging system, and presents the basic classification of cameras. The fourth chapter discusses various areas of application of thermal imaging, with an emphasis on its application in the power system. The fifth chapter presents basic concepts and classifications of distribution substations that connect medium-voltage and low-voltage networks. The sixth chapter presents images and results of thermal imaging inspections carried out on several 10/0, 4 kV substations. By reviewing the thermograms shown, results on the current state of the substations were obtained and recommendations for their maintenance were given.

Abstract: The aim of this final paper was to present the current conditions in an asymmetrically loaded two-winding transformer for typical examples of single-phase or two-phase asymmetrical loading. Three-phase power systems can be divided into symmetrical and asymmetrical systems. In the case of non-symmetrical systems, the problem of asymmetry is usually solved using the method of symmetrical components. On the examples of a two-phase asymmetrically loaded transformer on the side of a delta-connected winding, a two-phase asymmetrically loaded transformer on the side of a star-connected winding and a single-phase asymmetrically loaded transformer on the side of a star-connected winding, the transformation from an asymmetrical to a symmetrical system is shown in detail using the method of symmetrical components. The previously presented theory was analyzed and confirmed in laboratory conditions.

Abstract: Combined measuring transformers are a combination of voltage and current transformer. The most commonly applicable solution consists of a combined transformer with an inverse current transformer and an inductive voltage transformer. Measuring transformers of all manufacturers should comply with the international standard for measuring transformers under the designation IEC-61869-1. Additional requirements for combined transformers are found in the IEC standard under the designation 61869-4. In the fourth chapter of the work, a comparison is made between the manufacturers of Končar, Siemens and ABB combined transformers and, based on their characteristics, common characteristics are reached for oil combined transformers and combined transformers insulated with SF6 gas.

Abstract: The student should describe the basic concepts of the grounding system, types of grounding electrodes and analytical expressions that enable the estimation of grounding resistance from knowledge of grounding electrode geometry and specific soil resistance. Then, the methods of measuring grounding resistance and permissible values ​​according to current legislation should be described. The acquired knowledge should be applied to measuring the grounding resistance of several 110 kV transmission line poles and draw conclusions about the quality of grounding.

Abstract: The student should describe the characteristics of the Arduino platform, types of sensors, shape and amplitude of the input signal, signal processing method, output signals, communication with input and output units, and Arduino programming. After that, using the appropriate sensor, the Arduino platform should be configured to work as a contactless ammeter with wireless transmission of measurement data. The measurements obtained with such an ammeter should be compared with a commercial device and the accuracy class determined.

Abstract: This final paper analyzes the induction transformer, its equations, the vector diagram of an ideal and real transformer, and explains the properties of transformer oils. Special emphasis is placed on oil-immersed transformers and oil. Power transformers are most often oil-immersed transformers whose windings, together with the core, are placed in a boiler with oil. Whether it is mineral or synthetic oil, they have their own requirements and physical and chemical properties that need to be well known. By checking the oil, it is possible to predict future failures and avoid major damage. The measurement method used in the paper is measuring the breakdown strength of transformer oil with a Megger OST 80PB. All results presented in the paper were obtained from field testing. This method shows that adding water (water from the atmosphere and cellulose paper) has a negative impact on the dielectric strength of the oil. The quality of the oil deteriorates and it is necessary to replace or treat the oil. The purpose of this work was to familiarize the student with equipment for testing transformer oil, distribution transformers, their application, importance in the power system and maintenance of the transformers themselves.

Abstract: This paper explains power transformers, their application, division and function in the power system. Their principle of operation, basic laws and relationships are also explained. Special attention is paid to the isolation of power transformers and their testing and maintenance. Each transformer differs according to power, voltage and performance, and there are numerous different versions of their insulation. The condition of the insulation is very important for the reliable operation of the transformer. By checking the condition of the insulation, it is also possible to predict failures that often cause large costs. There are several types of insulation testing that can be classified into two basic types: direct current testing and alternating current testing. Testing with alternating current gives a much better insight into the state of the insulation because it enables the testing of inter-turn insulation, and the insulation itself is loaded with alternating voltage during operation. However, the equipment required for alternating tests is much more expensive and bulky, which makes it unusable in field tests. In the aforementioned paper, several results of field testing of isolation of oil distribution transformers with direct current are also listed and explained. The purpose of the work was to acquaint the student with the equipment for testing the state of insulation of electrical devices, its application, and familiarization with distribution transformers, their application, importance in the power system, and maintenance of the transformers themselves.

Abstract: This final paper presents in detail voltage measuring transformers, their divisions and various applications. Voltage measuring transformers from TS 110/35/10 kV Vrboran are presented in particular. The second chapter of the paper presents the basic characteristics of voltage measuring transformers and the influence of these characteristics when selecting a transformer. It also discusses the very important effect of ferroresonance, which can lead to various phenomena: from errors transmitted via the transformer to measuring devices to the destruction of the voltage measuring transformer itself. The third chapter lists all divisions of measuring transformers and also discusses the insulation of voltage measuring transformers. Inductive and capacitive voltage measuring transformers are presented in particular. The fourth chapter presents in detail all voltage measuring transformers located in TS 110/35/10 kV Vrboran.

Abstract: This final paper describes current measuring transformers, their application and classification. Their operating principle is also explained and they are compared with power transformers in characteristic operating states. The second chapter discusses current measuring transformers in general, their design, connection methods and their behavior in no-load and short-circuit conditions. In no-load conditions, large overvoltages occur and the transformer is destroyed, therefore the secondary must never be left open. Each current measuring transformer is defined by current and angular errors and accuracy class. Their explanations, calculation methods and the impact of reducing the number of turns of the secondary winding are discussed in the third chapter. The fourth chapter explains the behavior of a current measuring transformer in conditions of increased primary current, methods of obtaining a current multiplier and the selection of current transformers. The last chapter presents in detail the characteristics of all current measuring transformers located in the TS 110/35/10 kV Vrboran.

Abstract: In this paper, high-voltage SF6 circuit breakers are analyzed - their origin, history, use and production. The method of handling SF6 gas, safety during work and the chemical structure of SF6 gas are described. A comparison of the characteristics and capabilities of different types of high-voltage SF6 circuit breakers, manufactured by Končar, Siemens and ABB, was performed. The comparison was made by types of SF6 switches and by voltage levels. An analysis of the reliability of SF6 switches manufactured by Končar was also performed based on data on their failures.

Abstract: Through the first part of the paper, industrial plants, technological equipment and types of industrial plants are theoretically defined. Oil refineries are also defined, refining procedures and products are described. In the second part of the work, attention is paid to the design of the electric power supply and distribution system in the oil refinery, as well as the elements of electric power plants. The concept of selection and the importance of certain parts of the plant for constant power supply are explained. The final part shows the importance of the stability of the power supply itself and the possible solution of achieving a constant power supply through other sources and the use of a system for quick load shedding.

Abstract: The student should address the issue of air quality from a health and technical perspective and describe different measurement methods. Using the Fluke 975 V Air system, air quality parameters (temperature, relative humidity, dew point, condensation temperature, CO2 and CO concentration) should be measured for various measurement points within the FESB building, in the building environment and other suitable locations and compared with legally defined limit values.

Abstract: The student should address the issue of dust in the air from a health and technical perspective and describe different measurement methods. Using the Fluke 985 HHPC system, the student should measure dust concentrations and classify dust according to particle diameter for different measurement points within the FESB building and in the building environment as well as at other suitable locations and compare them with legally defined limit values.

Abstract: The student should describe the principle of operation of an induction transformer, transformer equations, vector diagram of an ideal and real transformer, and materials for windings and core. Special attention should be paid to techniques for measuring the transformer’s transfer ratio. Using appropriate equipment, perform measurements on 10/0, 4 kV/kV transformers of different powers in different tap changer positions and draw conclusions about the correctness of the transformer from the aspect of the transfer ratio.

Abstract: The student should describe the structure, use and properties of optical cables and measure the parameters necessary to verify their correctness. Using the Fluke DSP-2000 system with FOM and FTK accessories, the student should measure the relevant parameters (loss, power…) and conclude whether the cable meets the requirements for its category.

Abstract: The student should describe the construction, use and properties of LAN cables and measure the parameters necessary for LAN cable certification. Using the Fluke DSP-2000 system, the student should measure the relevant parameters (attenuation, NEXT, ACR, FEXT, delay difference, return loss, impedance…) and conclude whether the cable meets the requirements for its category.

Abstract: The student should describe the characteristics of the Arduino platform, sensor types, input signal shape and amplitude, signal processing method, output signals, communication with input and output units, and Arduino programming. After that, using the appropriate sensor, the Arduino platform should be configured to work as a solar radiation intensity meter. Compare the measurements obtained with such an instrument with a commercial device and determine the accuracy class.

Abstract: The student should describe the characteristics of the Arduino platform, types of sensors, signal processing, output signals, communication with input and output units, and Arduino programming. After that, the student should configure the Arduino platform to work as a thermo-hygrometer using the appropriate sensor. The measurements obtained with such a thermo-hygrometer should be compared with a commercial device and the accuracy class determined.

Abstract: The student should describe the working principle of the induction transformer, the transformer equations, the vector diagram of the ideal and real transformer, and the materials for the windings and core. A special review is given to the techniques of measuring the resistance of transformer windings. Using measuring systems UT 206 A and Megger AVO DLRO 10, perform measurements on transformers 10/0, 4 kV/kV and 35/10 kV/kV of different powers and draw conclusions about the correctness of the transformer from the aspect of the amount of winding resistance.

Abstract: As part of the final work, it is necessary to create a cheap and efficient circuit for measuring the frequency of the power system using the Raspberry PI platform. The corresponding program should convert the measured values ​​from the sensor into corresponding physical values ​​with eventual calibration. Computer support should enable the choice of different averaging intervals of the measured quantity. In addition, the developed solution should ensure periodic reading of the frequency along with the time stamp of the reading with the possibility of sending data to a cloud service that enables free storage and downloading of chronological measurement data. To examine the precision of various designs of circuits and algorithms for frequency measurement in relation to the available reference measurements.

Abstract: In this paper, the scope of functions related to the automation of distribution networks is defined. The paper explains the reasons for the introduction of new remote control systems, defines distribution network control models, and defines the basic characteristics of modern remote control systems. Below we have described the Distribution Network Management System (DMS). The main functions are explained in more detail, which include, among other things: consumption management, Q/U voltage regulation, calculation of electricity consumption and billing in accordance with current market prices, management of distributed power plants and elements for storing electricity, locating faults in the network, maintaining the quality of electricity , network reconfiguration and power restoration…

Abstract: As part of the final thesis, an application was created that allows displaying an Android GPS heat map, tracking the user’s location in real time, and inputting GPX files on the basis of which a heat map is created. The functioning of the GPS system and navigation devices is explained in detail. The Android operating system, its most important components and their use are also shown. The creation of an Android application, programmatic retrieval of the user’s location, use of the Google Maps API, and creation of heat maps using it are explained.

Abstract: The first part describes the historical development of the electricity market, which has been followed by electrical companies since the eighties of the twentieth century. For years, the electric power sector was a vertically integrated monopoly in state/private ownership, which, as a model of the organization of the electricity market, proved ineffective due to the unrealistic price of electricity. This, along with technological progress in the production and transmission of electricity, imposed the need for reform, i.e. liberalization of the electricity market. The only competitive market results in positive effects for all participants in market competition. This prompted a series of reforms throughout the world. Restructuring, regulation and privatization of the electric power sector took place. The reasons for the restructuring are also listed. Over time, the basic models of the organization of the electricity market are formed. We distinguish between three basic models, the model of vertically and horizontally integrated monopoly, the model of one customer and the market model that can be organized as a wholesale market and retail. The second part describes the main participants in the electricity market, as well as their roles and responsibilities. In the third part, the ways of determining the price of electricity in market conditions are briefly described. Price formation is a complex process that requires reaching a compromise between different interests and expectations. Finally, in the last chapter, an overview of the electricity market in the Republic of Croatia was made. Development of the electricity market. of energy is a continuous process that adapts to technical, economic and liberalization requirements.

Abstract: Through the first part of the paper, primitive network matrices, incidence matrices, and the method of their formation are theoretically defined. In the second part of the paper, the procedures for forming the impedance and admittance matrix of the node are listed and processed. In the last part of the work, expressions for the calculation of currents through the branches and node voltages in the event of a three-pole short circuit were derived. Finally, on the example of the electrical network, a comparison was made of the results obtained for currents through the branches and voltages on the busbars, obtained with the help of a program developed in the MATLAB environment, with the results obtained with the help of the TOKSwin program package.

Abstract: The paper describes the materials used for the construction of transformers, and the types and consequences of the resulting losses. It is also explained how losses can be minimized during construction. Loss calculations were made for three characteristic transformer drives: •sine balanced •sine unbalanced •non-sine balanced system. Within the program package MATLAB an algorithm was developed and implemented for the optimization of the substation drive in order to minimize the losses of working energy while avoiding frequent switching operations at the substation level. Based on historical consumption data at the substation level and electrical parameters of the transformer, the schedule of optimal switching states was determined.

Abstract: The paper describes the basic elements, types, method of execution and characteristics of distribution transformers. In addition to the main parts of the transformer, other additional parts of the transformer that may exist in certain versions are described. Ways to protect transformers from internal and external faults are also explained. The characteristic ways of grounding the constellation of medium voltage networks and the advantages and disadvantages of each design are described.

Abstract: The paper describes the physical basis of water power utilization, the basic parts, the method of execution and the types of hydroelectric power plants. The method of calculating the hydro potential and determining the possible production of electricity from the hydro power plant is described, along with the previous calculation of all losses or the total utility of the hydro power plant, based on which the type, number and power of the hydro unit is selected.

Abstract: The problem of optimal economic involvement of power plants in traditional systems boils down to satisfying consumption in the system by producing electricity from available power plants while minimizing the costs of their operation. When forming the plan of operation of the power plants, it is necessary to take into account the limitations of the production units that affect the possibility of placing energy at a regulated moment in time. In addition to covering consumption in the system, it is also necessary to take into account losses in the transmission of electricity to end consumers. In this paper, the theoretical basis for the calculation of the optimal engagement of power plants will be given, and a computer program will be developed that will enable the calculation of the optimal engagement of power plants in a system of realistic dimensions. Using specific examples, the developed computer program will be implemented and its characteristics will be described.

Abstract: In the introductory part of the paper, the problem of today’s energy and energy sources is briefly explained, and how more and more countries are turning to the production of electricity from alternative sources. In the second part, the physics of wind formation, its movement in the atmosphere, the influence of height and the surface of the earth on wind intensity and parameters for the assessment of wind potential are discussed. Different heights, as well as the surface itself, greatly affect the movement of the wind, and it is very important to place the wind farm in the right place. Also, there are certain parameters that should be taken into account and which are very important for the creation of wind farms in a certain location. In the third part of the paper, wind turbines, different forms of land-based wind turbines, components and materials used in making wind turbines, and the type of generator and mechanical connection with the turbine are covered. There are many forms of wind turbines that have been developed over the past as well as different materials, and research is still ongoing for even better refinement. In the fourth part, the aerodynamic conversion of wind on wind turbine blades is explained, what is the maximum utilization of wind energy, and how we use the blades and the angle of attack of the wind to regulate the workforce. Furthermore, how are buoyancy and drag forces created and why are these two forces one of the most important forces in wind turbines. The fifth chapter discusses the current state of wind energy in Europe and Croatia and what are the predictions for the future in that sector.

Abstract: In this paper, the task was to describe the basic principles of a cathodic protection system. In the second chapter, we explained: electrochemical corrosion, the process of cathodic polarization, the strength of the corrosion current, the electrolytic potential, the imposed protective potential that is needed to protect the structure from corrosion, and the conditions under which they must be met for the use of the cathodic protection system. In the third chapter, we described two cathodic protection systems, the system with an induced current and the system with sacrificial anodes, and gave their basic characteristics and areas of their use. We analyzed the potential distribution along a pipeline of limited length. We examined the type of anodes used in each of them, analyzed the time and efficiency of the anode operation, and the strength of the protective current. In the case of the induced current system, the power stations that provide the protective current are described. At the end of the chapter, we compared both systems for the purpose of their selection. In the fourth chapter, an example of the use of cathodic protection with an induced current for the protection of a steel pipeline is reviewed. The chapter describes the necessary measurements on the basis of which a decision is made on the technical solution and the basic elements of the system. The selection of anode bed, feeding station and operating mode for the selected example is presented. This chapter is intended primarily to gain insight into the necessary protective current and potential values ​​that ensure pipeline protection. The cost of pipeline maintenance, with and without a protection system, is also compared.

Abstract: This thesis describes the problem of assessing the risk of damage from lightning strikes and based on this, results were obtained using the DEHNsupport software package. After the introduction, the second chapter explains the concepts of damage and loss, as well as risk and its components, and provides factors that influence risk components. The third chapter lists the basic guidelines for risk management, which include identifying the object to be protected, the procedure for calculating the necessity and economic justification of protection, and the selection of protective measures. The fourth chapter discusses in detail the assessment of risk components for a building and provides all the formulas necessary for the assessment procedure. The concept of a zone in a building is also introduced and the assessment of risk components in a building with multiple zones is explained. The fifth chapter contains an introduction to the program, as well as the processing of examples using it. The calculation procedure using the aforementioned program is elaborated in detail. After the calculation itself, the economic justification of lightning strike protection as well as protective measures are explained based on the results.

Abstract: In this paper, the task was to describe the basic features of the medium-voltage shipboard electrical power system used on large ships with electric propulsion. In fact, these are voltages above 1000 V, which are high voltages for ship applications with an upper limit of 15 kV. In the second chapter, we gave a general overview of the functioning of the shipboard electrical power system, and in a separate subsection, we explained the reason and method of introducing high voltage, as well as its basic characteristics. The third chapter shows several typical schemes of shipboard high-voltage electrical power systems. The fourth chapter describes the basic energy sources, typical generators used on ships, and emergency power sources used when primary energy sources are disabled. The fifth chapter provides an overview of systems and devices for energy distribution and transmission, from electrical networks, through transformers and switchboards to types of converters. In the sixth chapter, we presented the basic features of electric propulsion and the types of motors used, from motors directly connected to the grid, motors with variable speed. We also described the latest concepts of electric propulsion, azimuth thrusters and pod propulsion. The seventh chapter talks about consumers of electrical energy, primarily about electric drives, which are the main consumers of energy at the medium voltage level. Since any contact with high voltage can be fatal, special attention should be paid to safety procedures to protect the devices in the first place from ground faults, and the personnel working with these devices. This was discussed in the eighth chapter.

Abstract: The task of this paper was to describe ship electrical systems, so the ship was considered as a separate electrical power system. The systems for the production, transmission and consumption of electrical energy are described. The medium-voltage ship electrical power system, safety and protection measures are also briefly described, and the history of ship electrification is also touched upon. The introductory chapter briefly discusses the development of ship electrification and briefly touches on sources, consumers and transmission of electrical energy on board. The second chapter discusses in more detail the main and auxiliary sources of electrical energy, i.e. generators, batteries, shore connection and uninterruptible power supply. The third chapter generally discusses ship electrical networks, electrical energy distribution systems and transmission systems for electric propulsion. The fourth chapter describes electrical energy consumers, which are divided into four subchapters. The first subchapter describes electric motor drives, the second describes circuit consumers, the third describes lighting consumers, while the fourth subchapter lists other consumers. Chapter 5 discusses the medium-voltage shipboard electrical power system and the protection of shipboard electrical equipment and persons on board. It also discusses the protection of ships from lightning strikes.

Abstract: The first step in the work was to solve the theoretical basis for the fixed method. This method previously required the formulation of an expression for the potential distribution in a multilayer medium. The medium was defined as multilayer where the first layer was air. The basic expression that had to be determined was the potential distribution, so the electric potential could be given by the expression of the Helmholtz differential equation. Immediately in the first calculations, an assumption for the wave constant was introduced in order to bypass the Sommerfeld integrals, and the Poisson differential equation was obtained. The retardation factor was included in the expression later. Then, a solution to the Poisson differential equation was derived and an expression was obtained that contained two kernel functions. Further calculations were actually based on the adaptation and approximation of these two kernel functions at the boundary values, and 25 points were taken for the approximation, and finally the retardation factor was introduced. The second step was the complex method and one of its forms, which is called the matrix bundle least squares method. This method focused on the Green’s function, whose expression was written in a general form. The key point here is that it was necessary to take into account that this is a cylindrical coordinate system and the Green’s function was written for such a case. The expression for the closed Green’s function was obtained using the Lipschitz integral and introducing the above substitution. In the end, an expression was obtained in which almost every part of this expression represents a quasi-static image and the electromagnetic field was considered quasi-static, which is why this method was called the quasi-static method of complex images. The matrix bundle least squares method is a method that gives approximately accurate results despite the occurrence of numerical errors and noise. By using matrices and substitution, the error and noise are nullified and a more precise method is obtained than the ordinary matrix bundle method. Finally, a numerical solution is given, as well as graphical examples and the procedure for calculating the expression for a three-layer and four-layer medium, and a conclusion is given on the relationship between these two methods.

Abstract: In this paper, the task was to describe the basic theoretical assumptions of static electricity. In the theoretical background, we defined some terms such as: electric field, electric field strength, electric potential, electric current, influence, polarization, electric displacement vector, capacity, work and energy in an electric field, and force in an electric field. In the third and fourth chapters, we described the formation of static electricity and its appearance in everyday life. In the fifth chapter, we looked at the possible dangers and damages caused by the discharge of static electricity. We also touched on atmospheric static electricity in the sixth chapter. The focus of the work is on the description of methods for protection against the harmful effects of static electricity. The seventh chapter talks about measures to protect against static electricity, by which we mean: grounding, maintenance of adequate humidity in the air, air ionization, antistatic preparation, increasing the conductivity of poorly conductive materials and removing static electricity by influence. We also touched on protective measures in explosive environments, protection of flammable and poorly conductive liquids, personal protection and protection in industry. In order to implement protective measures at all, it is necessary to regularly measure static electricity with appropriate instruments. This was discussed in chapter eight.

Abstract: This final paper explains, based on available literature, why the quality of electricity is important and how to check its quality. Since electricity is a commodity sold on the world market, it is determined by various standards, including standards on the quality of electricity. The second chapter describes the concept of electricity quality and the EN 50160 standard that refers to it. The third chapter contains a brief description of the characteristics of electricity quality, and most of this final paper is dedicated to this, and the fourth chapter describes the need for measuring electricity quality and certain methods. The fifth chapter describes the Fluke 435 power quality analyzer and how it is connected and used. It describes its capabilities, functions, how to connect to the network and some additional parts, and shows catalog data. The sixth chapter contains the results of measuring the quality of electricity in the FESB building. These results are presented graphically and it is clearly seen that the electricity in the FESB building meets the criteria set by the EN 50160 standard and on the basis of which the Fluke 435 analyzes electricity. The reason for this is that we had an unloaded consumer and were relatively close to the transformer station, so no significant fluctuations in the monitored electricity parameters were observed.

Abstract: The task of this paper is to classify chemical sources of electrical energy and briefly describe the basic characteristics of primary and secondary chemical sources of electrical energy. The introductory chapter defines the meaning of a battery as a chemical source of electrical energy, the difference between a battery and a cell, and a wide range of applications for the same. The second chapter provides a description, the history of the creation of a battery, and a general division into primary and secondary chemical sources of electrical energy. It also defines the concepts of electrode potential and electrical polarization. The third chapter classifies and describes primary chemical sources of electrical energy, starting from the oldest and technologically simplest cells (Voltaic, Weston’s), all the way to the technologically more modern mercury, alkaline, and silver batteries. The fourth chapter provides a division, description, and application of secondary chemical sources of electrical energy, as another large and important group of chemical sources, which today have a very wide range of applications. The final fifth chapter provides insight into some more modern technologies, which are increasingly being researched and advanced, as possible successors to current sources. A brief description of future technologies such as supercapacitors, fuel cells, and nuclear batteries is presented.

Abstract: In this final paper, based on the available literature, the most commonly used methods for assessing the geoelectric properties of soil are systematized. The measurement methods and methods for interpreting the measurement results are briefly described. After which, using the EarthModel software package, the results of measuring the apparent soil resistivity during geoelectrical sounding are interpreted. The first chapter provides a brief introduction, listing the basic geoelectrical parameters of the soil. After which, the methods used for assessing the geoelectrical properties of the soil and the reason for their application are listed. The second chapter describes the geoelectrical sounding method, measuring using the Wenner and Schlumberger methods, and the method of measuring and determining the apparent resistivity from the measured data. The third chapter briefly describes the surface impedance method and the method of measuring the field and soil impedance. The fourth chapter refers to the wave propagation method, the method of calculating the surface impedance and its application in wells or underground. The fifth chapter describes the wave rotation method, measurement techniques, and wave rotation equations. The sixth chapter describes the probe impedance method, i.e. the basic methods for measuring the electrical properties of the soil, the method of determining the input admittance of a transmission line and the electrical parameters of the soil. After that, measurement techniques and applications in boreholes are explained. The seventh chapter describes the mutual impedance method, the basic antenna structures and the method of calculating the mutual impedance for a particular structure are given. After that, measurement techniques and methods in boreholes or underground are described. The eighth chapter describes transient electromagnetic methods and the method of calculating the soil conductivity and the pulse measurement method is described. The ninth chapter describes the time-domain reflectometry method, the method of execution, measurement techniques and the calculation of impedance and reflection coefficient. The tenth chapter describes resistance measurement in the laboratory, the method of execution and determination of the apparent soil resistance. The eleventh chapter describes the capacitance method, the method of execution and the procedure for determining the dielectric constant of the soil. The twelfth chapter provides the theoretical basis for interpreting the results of measuring the apparent resistance using the EarthModel software package, after which an example of interpreting the task in the EarthModel software package is given.

Abstract: In this final paper, based on the available literature, various aspects of electricity quality are briefly reviewed, with special attention paid to the influence of the characteristics of the grounding system on the quality of electricity. Electricity is a commodity traded on the open market, which must meet the given quality criteria. Therefore, the main part of this paper is dedicated to the basic characteristics of electricity quality, the basics of the grounding system and the methods of measuring the disturbances themselves, as well as the quality of electricity itself. In the second chapter, in addition to the concept of electricity quality, some of the standards related to quality are described, namely the purpose and characteristics of these standards. The third chapter refers to the characteristics of electricity quality. A detailed description of the characteristics of all parameters is given here. In the fourth chapter, the influence of the grounding system on the quality of electricity is discussed, since the grounding system and the method of grounding have a great influence on the quality of electricity. In the fifth chapter, methods of measuring the quality of electricity are discussed, with a description of the capabilities of existing devices for measuring the quality of electricity. Power quality monitoring requires specially developed methods for calculating power quality characteristics and clearly defined limits for these characteristics for comparison with measured values. In the same chapter, some of the methods of power quality monitoring using newer devices such as the FLUKE 435 are described.

Abstract: The introductory chapter discusses the current IEC/EN 62305 standards. These are standards in the field of lightning protection. The third chapter discusses sources of damage with respect to the location of the lightning strike, types of damage and losses. Furthermore, the fourth chapter describes risk, types of risk and risk management based on its components. The decision on the need for protection is made based on existing standards. Optimal protective measures are selected with respect to technical and economic aspects. The fifth chapter deals with the design of lightning protection systems, where methods for designing the arrester, down conductor and grounding systems are listed. Three methods of the arrester system are listed: the rolling ball method, the protective angle method, the conductor network method. The conductor network method is used in the demonstration example. When designing the down conductor system, natural down conductors and the measuring connection are mentioned. In designing the grounding system, there is a type A system and a type B system. An example of a building with lightning protection is in the sixth chapter. All data that serves as criteria for selecting the type of protection is listed. A lightning protection calculation has been performed for a car mechanic workshop.

Abstract: In the introductory part, we defined overvoltages. We consider overvoltages on devices to be unwanted and dangerous phenomena because they endanger the safety of personnel, damage or completely destroy devices and cause malfunctions of devices. We can effectively protect a device from overvoltages if we know the characteristics of overvoltages well. One of the basic characteristics of overvoltages is the place and method of occurrence of overvoltages, i.e. the source of overvoltages. Overvoltages on LV installations are caused by: direct lightning strikes, indirect lightning strikes, switching on and off in the power system, switching on and off in LV installations themselves, etc. Knowing the source of overvoltages, we design a system for protection against lightning and overvoltages. The task of overvoltage protection is to conduct all excess energy caused by overvoltages past the protected equipment to the grounding system in the shortest possible time. In addition to the electrical characteristics of the arrester, the response speed is also an important feature for selecting protection. Since fast protective elements cannot meet the energy requirements, multi-stage protection is resorted to, and combinations of fast and slower, but more energy-efficient protective elements are used. In the end, we determined the method of choosing the appropriate surge protection device for low-voltage systems, which is based on a probabilistic approach.