Influence of Short-Circuit Current Nonperiodic Component Increasing on Radial Dynamic Stability of Power Transformer Winding Under Reclosing

Abstract

As one of the key main equipment of the power system, the transformer directly affects the safe and reliable operation of the system. In the process of transformer reclosing, the internal electromagnetic environment is obviously different from that of the initial short circuit. The nonperiodic component of the short-circuit current exceeds that of the initial short circuit, increasing the electromagnetic force on the winding and severely threatening its dynamic stability. In order to study the influence of reclosing short-circuit impact on the radial dynamic stability of transformer winding, this paper takes SFSZ9-50000/110 transformer as an example. Firstly, the numerical model of short-circuit current of infinite power system is constructed by Matlab/Simulink, and the short-circuit current of initial short-circuit and reclosing process is calculated. The increase value of the reclosing short-circuit current compared with the initial short-circuit current is calculated, and the accuracy of the short-circuit current numerical calculation model is verified by comparison with the theoretical value. The results show that for the power transformer studied in this paper, the three-phase short-circuit current of the transformer under the reclosing short-circuit condition increases by about 6% compared with the initial short-circuit current. Then, based on the short-circuit current, the finite element method is used to analyse the leakage magnetic field of the transformer winding by using ANSYS Maxwell and the variation law of the electromagnetic force under the reclosing short-circuit impact. Finally, various kinds of radial stress of transformer winding under initial short-circuit and reclosing short-circuit conditions are compared and checked. The results show that under the reclosing condition, the average circumferential stress and inner winding radial bending stress of the transformer increase by about 12%, which leads to the decrease of the dynamic stability margin of the transformer. The research results have reference significance for optimising the dynamic stability verification method of transformer winding under reclosing short-circuit impact.