Profile optimisation for an HV insulator in vacuum

The exposition of HV solid insulators in a vacuum to relevant voltage differences could determine the surface flashover along the solid dielectric-vacuum interface. Insulator holdoff capabilities can be significantly improved by limiting the field intensity in proximity of the electrodes by means of geometrical field control, namely designing the insulator profile so that the region subjected to high field is shifted away from the regions where the electrodes join the solid dielectric-vacuum interface. In this paper, a new profile for an HV insulator in a vacuum is presented. An axially symmetrical configuration constituted by a couple of coaxial cylindrical electrodes is considered, with the insulator shape designed to guarantee similar performances for both field polarities. The effectiveness of the design is validated by means of numerical simulations and by experimental results involving DC and impulse flashover performances.