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.