The effect of trigger electrode on the initiating of surface flashover on insulator surface in vacuum

The surface flashover on the insulator surface of disk-type aluminas YAS 998 held between a backside electrode (alumina holder) and a needle electrode to be excited by an impulse voltage (rise time 64 μs, wave tail 700 μs) has been investigated. The backside electrode is completed with the trigger electrode that inserted close to the insulator surface and located at the opposite edge of the backside electrode. From the measurement of surface charge distribution for unflashover condition revealed that the presence of the trigger electrode was not significantly influenced in the initiating of surface charging. For positive impulse voltage application, the anode played an important role in the initiating of surface charging (the anode region is positively charged), while for negative impulse voltage application the cathode region played a role in the initiating of surface charging (the cathode region is negatively charged). During surface flashover condition (positive and negative impulse voltage application), the image of the surface flashover pictures showed that light intensity is concentrated both on the anode and cathode region