Electric Surface Strength and Surface Deterioration of Thermoplastic Insulators in Vacuum

Investigations have been made of various factors which effect the surface flashover strength across thermoplastic insulators in vacuum. The factors studied, for ac and dc excitation, included the dependence of flashover voltage on specimen length, metallization of the insulator ends, specimen conditioning under dc and ac voltages, and residual gas pressure. The influence of the number of sequential flashovers on the flashover voltages and on the surface deterioration of polymethylmethacrylate, tetrafluoroethylene, and polyethylene samples, in vacuum, has also been determined. Tree tracks were examined under an electron microscope to determine their growth and characteristics at different stages of the experiment.