Investigation on developing process of impulse flashover across alumina ceramic with asymmetric electrodes in vacuum

Summary form only given. Flashover phenomena in vacuum restrict the performance of insulation system, which has been paid much attention by many researchers. However, due to the rapidity and complexity of flashover development process, the mechanism of surface flashover phenomena is still not fully understood. In this paper, an ICCD camera is adopted to observe the dynamic process of surface flashover on alumina ceramic in vacuum under impulse voltage. A needle as the HV electrode and a round-shaped steel as ground electrode are placed on the alumina ceramic, which forms an asymmetric electrodes configuration. Negative and positive impulse high voltages are applied on needle electrode, respectively. And the development processes of surface flashover are investigated. The results show that when negative voltage is applied on needle electrode, light emission always starts from cathode and then move to the anode, while positive voltage is applied on needle electrode, due to high electric field near needle electrode, light emission can be observed both at cathode and anode. But at the anode, the light emission region is limited in a small scale. It can also be seen that light emission near the cathode is developing to anode with applied voltage increasing, and the light branches are only developed in the direction of anode.