The Influence of Flashover Traces on Partial Discharge and Flashover Characteristics of Insulator in SF6

Gas insulated equipment is widely used in substations and converter stations due to its good properties. However, insulation failures of gas insulated switchgears (GISs) and dead circuit breakers (DCBs) occur occasionally on site, and flashover traces have also been found on the insulator surface in some normally operating DCBs. The influence of flashover traces on insulation performance is still unclear. In this paper, a 550-kV test platform is established. Partial discharge (PD) and flashover tests of metal particles on the insulator surface are conducted, and the influence of flashover traces on PD and flashover are studied. The results show that, the 8 mm long metal particle will significantly reduce the flashover voltage. Before flashover, the discharge is sporadic and weak, and the apparent charge is normally lower than 5 pC. The repetition rate of pulse current signal is lower than 200 times/s, and only over a hundred ultra-high frequency (UHF) signals appear before flashover. With only flashover trace on the insulator surface, the flashover voltage is 400 kV, which is higher than that with metal particles but much lower than the AC withstand voltage. The total number of discharge signals is less than 100 before flashover. This study helps to understand the influence of flashover traces on insulation performance, providing support for condition monitoring, diagnosis, and evaluation.