Spacer Flashover Characteristics in SF6 Under Repetitive Nanosecond Pulses

Very fast transient overvoltages (VFTO) may result in insulation failures inside or outside gas insulated switchgears (GIS), and most of them are caused by surface flashovers along insulating spacers according to operational experiences. For a good understanding of the discharge process produced by high voltage pulses with a fast rising time, an experimental study on spacer flashover under repetitive nanosecond pulses in high pressure sulphur hexafluoride (SF6) is presented. A solid-state pulse generator is used to generate nanosecond pulses with a rise time of 15 ns and a full width at half maximum of 30 similar to 40 ns. The pulse repetition frequency (PRF) varies from single shot to 1 kHz. Brass parallel-plane electrodes and cylinder epoxy resin spacer are used to represent a configuration of uniform electric field and insulator in GIS, respectively. In this experiment, the parameters of amplitude of discharge current, flashover time lag and number of applied pulses to flashover are investigated. And their relationships with gas pressure and PRF are analyzed.