Winding Overvoltage Characteristic Analysis of Modular Cascade Isolating Energy Supply Transformer of ±500 kV Hybrid HVDC Breaker

The 500 kV isolating energy supply transformer (HIET) with a modular cascade structure can serve as electrical power supply for ±500 kV hybrid HVDC breaker with high voltage isolating capability. Due to the mutual influence of HIET's stray capacitance, winding overvoltage (the overvoltage between the winding terminals) is induced by external overvoltage from HDCB, which significantly impacts on winding insulation design. In this paper, equivalent circuit models of 500 kV HIET are established. The circuit parameters extracting method is given, and circuit parameters are extracted. The winding voltage stress characteristics under lightning/switching impulse overvoltage and HDCB breaking overvoltage are analyzed. The simulation results show that the steeper the applied voltage wavefront, the greater the winding voltage stress peak. It is concluded that the stray capacitance uneven distribution of the winding terminals to ground has a significant impact on the winding voltage peak. By the 500 kV HIET prototype, the windings voltage stress characteristics are verified. The study provides a basis for the winding inter-turn insulation design, supporting the development of 500 kV HIET. It has been successfully applied and verified in Zhangbei ±500 kV DC Grid Project.