Correlation between insulator surface and DC flashover characteristics in vacuum

The high-voltage DC flashover characteristics of a large number of solid insulating materials were investigated. These materials included high-density aluminas from different manufacturers varying in bulk composition and surface microstructure, coated aluminas to reduce surface charging, steatite, and forsterite. The results show a strong correlation between the first and conditioned breakdown strengths, the rapidity of conditioning, and the surface microstructure. Specifically, it is shown that `generic alumina´ has widely varying voltage withstand strengths depending on the bulk composition, surface microstructure, and chemical surface state. Materials with a finely granular, closely packed structure exhibited the best voltage hold-off performance. Also, nonporous materials exhibit rapid conditioning to its final value