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.