Development process of impulse surface flashover on alumina dielectrics in vacuum

For higher electrical insulation performance of vacuum circuit breakers (VCB), the surface insulation characteristics in vacuum should be improved. In this paper, we investigated the development mechanism of impulse surface flashover on alumina ceramic insulator in vacuum. We measured the still images and ultra fast framing images of fast developing surface flashover in synchronous with applied impulse voltage and current waveforms. The light emission transition in initiation of surface flashover was also clarified. We found the dark area was formed around the cathode and conducting channel was formed from the anode in developing process of surface flashover in vacuum.