Calculation of Influence of VFTO Signal on Insulation of Main Equipment in 500kV Power Station

The very fast transient over voltage (VFTO) caused by switching operation in GIS power station may threats equipment insulation especially transformers to research this problem, EMTP is adopted to calculate the overvoltage in 500 kV power station and a dynamic arcing model is used to simulate arc resistance in disconnector to improve the calculation accuracy to analyze the influence of VFTO on interturn insulation by equivalent circuit model of transformer winding is established. Then amplitude waveform and frequency spectrum of VFTO by switching operation in transformer side and bus side is calculated and compared and the threat to equipment's major insulation is assessed, results show that VFTO caused by switching operation in bus side when the bus is charged is more serious; at the same time, the distribution of VFTO in transformer winding is calculated results show that high frequency voltage concentrates on the cokes and interturn near the winding entrance voltage of interturn 1–2 is the largest, which account for 5.9% of the entrance voltage.