Ultraviolet-Induced Flashover of Highly-Angled Polymeric Insulators in Vacuum

摘要

The flashover of electrically stressed polymeric insulators in vacuum induced by exposure to intense ultraviolet radiation was investigated. Two geometries, positive and negative 45 degrees, were studied at electric field stresses of up to 80 kV/cm. Insulating materials tested were polystyrene, acrylic, nylon-6, acetal, PVC, and teflon. A krypton fluoride excimer laser at a wavelength of 248 nm provided the ultraviolet illumination. Ultraviolet-induced flashover over polymeric insulators in vacuum depends on the ultraviolet fluence (energy density) incident on the insulator surface. The negative-angle (unconventional) configuration exhibits superior ultraviolet tolerance compared to the positive-angle (conventional) configuration by approximately a factor of two in fluence. Insulating materials with high dielectric constants and low secondary electron emission coefficients exhibit superior ultraviolet tolerance. A model of ultraviolet-induced insulator flashover based on induced charging of the insulator surface is sufficient to explain the observed phenomena. Theses. (mjm)