Formation of Charge Distribution Inside Alumina Cylinder under the Various Conditions of AC Voltage Application in Vacuum

Abstract

In order to improve the electrical insulation performance of Vacuum Interrupter (VI), it is important to control a surface flashover which occurs via charging on the insulator. In this paper we prepared a model sample of vacuum interrupter with shield rings which mitigates the high electric field around triple junctions. The charge distributions on the inner surface of cylindrical insulator were investigated after applying AC voltage under the various conditions. The charge distributions were measured over whole area of the inner insulator's surface by an electrostatic probe. As a result, we found that surface electrical charges were formed on some local parts of insulator surface between the areas of the shield rings after the initial stage of several cycles of AC voltage application. After AC voltage application during some seconds, the surface charges tend to expand all over the insulator surface. Additionally, depending on times of AC voltage application test, the formation of surface charges becomes more difficult. It was considered as the conditioning effect on the surface electrical charges.