In this paper, the mathematical modeling and simulation of electromagnetic transient processes is considered, which is of vital importance for examining the overvoltage phenomenon of power transmission systems. In the mathematical models of the AC power transmission systems that contain a power source, the power transformer, transmission line, and power autotransformer block are presented. The mathematical model of each system component is obtained based on the branch voltages, flux linkages,

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... d branch voltages of the magnetic circuits individually. As for the simulation, an alternative transient program (ATP) environment is used to model the electric power system's elements. One of the power system's overvoltages occurs because of the fault and switching events. The usage of reactors at the sending and receiving ends of the line limits the overvoltages. The ATP has a powerful tool to simulate the transient events: specifically, the fault transients in the time domain. In order to test the simulation model's performance, the overvoltage measurements from a field test of a 500 kV electric transmission system is used. The simulation shows that the obtained results give satisfactory solutions to investigate the power system's overvoltage events. Selected results of the evaluation are presented.