Charge behavior and partial discharge characteristics on alumina dielectrics under AC voltage application in vacuum

The charge behavior and partial discharge characteristics, which is not breakdown but has a potential to lead breakdown, at solid-composite system in vacuum can be a critical issue to be investigated, under ac operating voltage application. We investigate the partial discharge along an insulator surface in vacuum under AC voltage application by the measurement of the charging and the light emission. Under sudden AC high voltage application, the partial discharge along the alumina surface occurred at the peak voltage of the negative polarity. The partial discharge was initiated near the rod electrode and spread out over the whole alumina surface. By the analysis of electric field, the partial discharge and subsequent charging behavior on the alumina surface under AC voltage application was verified to be dominated by the distortion of electric field due to the negative charges accumulated on the alumina surface, and this distortion occurs at the period of decrease of negative applied voltage.