Estimation of flashover voltage along cylindrical insulator in vacuum

This paper deals with a method to estimate the surface flashover voltage of an insulator in vacuum, in which the distribution of surface charge accumulated due to a secondary electron emission avalanche (SEEA) is taken into account. We show experimental and calculated results for a cylindrical insulator made of ceramic, glass or polymer, where each insulator ranges up to 50 mm in length. Since the surface roughness of specimens affects the progression of SEEA, its influence on the flashover voltage is also examined. The calculation results have demonstrated good agreement with experimental ones except for a case in which the SEEA charge is substantially lowered. For further confirmation of the validity and applicability of our estimation method, we have examined the flashover characteristic of a specimen when its surface consists of smooth and rough regions. The calculation result of this case also agreed with the experimental one. To explain the disagreement that appears in the less charged case, we discuss and propose two flashover mechanisms, including one based on SEEA.