Role of surface charging in the breakdown of forty-five degree insulators subjected to high voltage nanosecond excitation

A bridged vacuum gap generally fails at a potential lower than that of a corresponding unbridged gap. For pulsed systems a 45 degree contact angle has been found to exhibit enhanced hold off capability. Despite the improved capabilities, the 45 degree insulator will ultimatly fail due to mechanisms which are not well understood. The results reported here attempt to correlate the existance of surface charge on an insulator with hold off capabilities. Results tend to indicate that the +45 degree insulator exhibits less charging than that for other angles resulting in less field enhancement and a resulting higher hold off capability.