Comparative investigations of DC and 60Hz prebreakdown behaviour of vacuum insulation

Vacuum insulation for high voltage power apparatus is becoming more acceptable. However, there is very little comprehensive data available for the insulation performance of vacuum gaps under 60Hz a.c. voltage stress. The authors report the result of a systematic study comparing the behaviour of a vacuum insulated gap under d.c. and 60Hz a.c. voltage stress. It is concluded that the behaviour of a vacuum gap is not significantly different for the different types of voltage stress except in the initial prebreakdown phase.