FLASHOVER OF INSULATORS IN VACUUM - REVIEW OF THE PHENOMENA AND TECHNIQUES TO IMPROVE HOLDOFF VOLTAGE

This paper reviews surface flashover of insulators, primarily in vacuu m, although some comments are made about the effect of ambient gases o n surface flashover. It presents theoretical mechanisms of surface fla shover and pertinent experimental results. The holdoff voltage of insu lators depends upon many insulator parameters, such as material, geome try, surface finish, attachments to electrodes, but also on the applie d voltage waveform, duration, single pulse or repetitive, and on the p rocess history of the insulator operating environment, and previous ap plications of voltage. Several suggestions are made regarding how to c hoose the material, geometry, and processing when selecting an insulat or for a particular application. Some specific techniques for improvin g the holdoff voltage of insulators are recommended.