Micro-discharge and surface flashover of insulators in vacuum

Recently surface flashover phenomena of insulators in vacuum were investigated with an impulse voltage (0.7/4 μs). The test samples studied were 99.9% alumina specimens. The impulse voltage, current and luminosity waveforms were observed whether a flashover occurred or not. Surface charges on insulator were also measured after impulse voltage application. Micro-discharge on the surface of insulators was observed in the experiments. The experimental results show that the micro-discharge occurs frequently as a kind of preflashover phenomenon and can be observed right before the current burst of flashover almost every time. It´s considered that the micro-discharge is related to the accumulated charges on the surface, which initiates a flashover