Inception and expansion process of surface flashover on solid dielectrics in vacuum

Surface discharge on solid insulator in vacuum, which is one of the most significant phenomena under high electric field, prevents vacuum circuit breaker and vacuum interrupter from applying to higher voltage level. To clarify the mechanism of surface flashover, we investigated the transiently-formed charge characteristics on alumina dielectrics in the development process of surface flashover, by using electrostatic probes behind alumina dielectrics and measuring the light emission image of flashover. As a result, we found out that charge distribution on the alumina dielectrics in the inception of surface flashover depends on the electron emission sites on the cathode and influences the expansion process of surface flashover in vacuum.