Spacer flashover characteristics in SF6 under repetitive nanosecond-pulses

Very Fast Transient Overvoltages (VFTO) might result in insulation failures inside or outside Gas Insulated Switchgears (GIS), and most of them are led to by the spacer flashovers in the light of operational experiences. To get a better understanding of the discharge process, an experimental study on spacer flashovers under nanosecond-pulses in compressed Sulphur Hexafluoride (SF₆) gases is presented. A solid-state pulse generator, SPG200N, is used to generate nanosecond-pulses with a rise time of 15 ns and a full width at half maximum of 30-40 ns. The pulse repetition frequency (PRF) varies from 1 Hz to 1 kHz. The material of spacer is epoxy resin, a common material as insulators in GIS. The test electrodes are brass parallel-plane electrodes, 80 mm in diameter, to simulate uniform field in GIS. In this research, the relations of flashover time lag with gas pressure and PRF are investigated. The experimental results show that the flashover time lag gradually rose with the increase of gas pressure under single shot and lower PRF.