Surface charge decay on HVDC insulators: Temperature and Field effects

The surface charge behavior on epoxy plates pre-charged by corona in SF₆ is investigated by surface potential decay measurements. The temperature dependence of the charge mobility estimated from surface potential decay is compared to the DC volume conductivity obtained from conventional current-voltage measurements. Furthermore, the effect of the temperature and the initial field on the charge decay mechanisms is studied. This is of particular practical importance for applications because considerable temperature gradients along the epoxy insulators in gas-insulated switchgears (GIS) separating the hot conductor from the cold ground can appear. Different surface charge controlling mechanisms may predominate at different locations on a GIS insulator.