The relevance of the research is caused by the need to define the required voltage level of the supply transformer with regard to the downhole reactive power compensator, in order to prevent accidents in operation of electric centrifugal pumps' plants. The aim of the research is to assess the change of voltage drop value in electrotechnical complex conductive elements of the electric center-pump plants for oil production using a downhole reactive power compensator. The research object is the electrotechnical complex of electric center-pump plants for oil production. Methods. Thesis of electrical engineering theoretical foundations, correct assumptions in preparation of mathematical models and computer simulation in the software package of symbolic mathematics Wolfram Mathematicain were used when developing the mathematical model of the electrotechnical complex of submersible plant for oil production. Results. The authors have developed the equivalent circuit and mathematical model of electrotechnical complex plant of electric centerpump with a downhole reactive power compensator. The distribution of voltage drop values in the complex elements is shown using the high-quality vector diagram of voltage and current in the branches and nodes of the equivalent circuit. The analysis of the vector diagram showed that the in-hole compensator reduces the longitudinal and transverse components of the voltage drop, which positively affects the mode of operation of the oil production plant. The surface of the required voltage at the output of the supply transformer is obtained depending on submersible electric motor power value for different lengths and sections of the cable line. It was found that the use of the downhole compensator makes it possible to reduce the voltage drop in the current-conducting elements of the electrical engineering complex of the oil production plant to 50 V.