Abstract
This article focuses on the insulation along solid dielectrics exposed to high voltages or high electric fields in vacuum. Solid insulators in vacuum acquire charge due to electron impacts. Coincidently with the impacts, adsorbed gas molecules are released from the insulator surface. Discharge, or flashover, occurs in the desorbed gas layer. As the amount of gas molecules is closely related to the surface charge distribution, charging phenomena are firstly explained from experimental and theoretical viewpoints. Then, the theory for estimating the flashover voltage is explained and its applicability is discussed based on the experimental flashover data for various materials and surface conditions.
