Study on the Maximum Step Voltage Calculation Method of On-load Tap Changer in Symmetrical Two-core Phase Shifting Transformer

The flexible control of power flow can be realized by the phase-shifting transformer, whose load conditions are complicated and the phase angle difference between the load side voltage and the load current will vary greatly. The on-load tap changer is a key component for the phase angle adjustment. The required breaking step-voltage of it is closely related to the on-load conditions in the process of shifting positions. Based on the working principle, operational characteristics and the calculation formula of the step-voltage under on-load conditions of the two-core phase-shifting transformer, this paper analyzed the effects of different load conditions including the load current, phase angle difference between the load voltage and load current and different operation modes on the step-voltage of the phase-shifting transformer. The changing regularity of the secondary side voltage of the exciting transformer is achieved and a novel method for calculating the maximum step-voltage is proposed. By analyzing two specific examples, the feasibility and accuracy of the method were verified by comparing the calculation results with the Matlab/SIMULINK simulation model.