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

This paper reviews surface flashover of insulators, primarily in vacuum, although some comments are made about the effect of ambient gases on surface flashover. It presents theoretical mechanisms of surface flashover and pertinent experimental results. The holdoff voltage of insulators depends upon many insulator parameters, such as material, geometry, surface finish, attachments to electrodes, but also on the applied voltage waveform, duration, single pulse or repetitive, and on the process history of the insulator operating environment, and previous applications of voltage. Several suggestions are made regarding how to choose the material, geometry, and processing when selecting an insulator for a particular application. Some specific techniques for improving the holdoff voltage of insulators are recommended.