Integrated modelling of vacuum flashover development: Above‐surface processes and breakdown threshold analyses

Abstract

The flashover in vacuum is a rapid interfacial discharge across the insulator surface when subjected to high applied voltage. Here a theoretical model covering above‐surface processes is introduced. The model calculates the flashover threshold in vacuum, with revised secondary electron emission avalanche theory and improved desorbed neutral transport model. The model serves as the first part of an integrated flashover model, aiming for consistent treatment of both above‐surface and subsurface processes during the entire flashover development. The flashover threshold is obtained by combining the desorbed neutral pressure at given applied voltage and the gas breakdown criterion dictated by the Paschen's law. An analytical formula for threshold estimation containing physical parameters, and a simplified formula consisting of empirical coefficients are introduced, catering for both conceptual understanding and practical application. The derived formulae are validated by experimental data for a variety of insulator materials. The theory generalisation for non‐uniform electric field distribution is further discussed.

Customizing superior surface insulation properties of polymeric dielectric via in-plane molecular chain orientation

“…Surface flashover, a ubiquitous surface electrical breakdown phenomenon that occurs at the interface of vacuum and dielectric surface, is usually triggered before the bulk breakdown of both vacuum and solid. Poor surface insulation property often leads to premature surface flashover, which has been the main factor severely constraining the operating voltage and durability of vacuum devices [1][2][3][4]. Clarifying the underlying mechanism of surface flashover and developing targeted methods * Authors to whom any correspondence should be addressed.…”

“…The complicacy of surface flashover lies in the fact that factors such as secondary electron emission [1,5], surface outgassing [4,6], and surface charge migration [3,4,7,8] are all thought to affect flashover. Among numerous factors, surface charge migration property, determined by surface composition and molecular chain structure, is particularly crucial [8].…”

“…This is because the reverse electric field formed by the accumulated charge can further inhibit primary charge injecting from cathode triple junction. However, it must be noted that when charge migration properties are changed by such mentioned composition-modulated modification methods, it is likely that other flashover-related factors are also changed [2,4,8]. Hence, the improvement of surface insulation strength shows variability and poor controllability.…”