Flashover across polyethylene and tetrafluoroethylene surfaces in vacuum under direct, alternating and surge voltages of various waveshapes

Investigations were made of various factors which affect the flashover values across polyethylene and tetrafluoroethylene surfaces in vacuum. The factors studied included sample conditioning under sustained direct and power frequency voltages, and the effect of surge voltage waveshape. The breakdown values for a given voltage waveshape increased with the time of conditioning up to a maximum value which then remained constant within about 10%. Alternating voltages were found to be more effective in the conditioning process. The average breakdown voltage for each insulator decreased with increasing the surge front duration from 1 μs to about 150 μs and thereafter remained constant.