This paper investigates the use of new technologies for primary current into secondary voltage electromagnetic sensor. In the monitoring and management of electric power supply systems around the world, great attention is paid to determining and standardizing the values of measured and controlled quantities and parameters based on signal transformation processes, to the accuracy and reliability of measurement indicators, and to the algorithms and practical software products that provide them. This scientific article is to develop three-phase electromagnetic sensor models and the principle of construction for measurement and control of reactive power of the power supply system. During the research, the methods of calculating the magnitude and parameters of electric and magnetic circuits, calculating errors, graphs, and signals, and designing and modeling electromagnetic converters were used. The practical results of the research are as follows: based on the requirements of power supply system reactive power management, a physical model of the three-sensitive element structure of the complete three-phase current-to-voltage secondary signal converter is developed. Electromagnetic converters of reactive power control systems of the power supply system are based on such quantities and parameters as electricity, magnetism, thermal, mechanical, physical and technical processes, distributed in most cases single and multi-field, rectilinear, non-linear, and also characterized by parameters. Modern calculations and design require the use of complexes in the study of electromagnetic converters of primary current into secondary voltage of complex and variable quantities.