Influence of Radius of Curvature, Contact Angle and Material of Solid Insulator on the Electric Field in Vacuum (and Gaseous) Gaps

The insulation strength of a vacuum gap bridged by a solid insulator is lower than that in the absence of the solid insulator. The triple junction formed by the solid insulator, electrode, and vacuum in vacuum devices (or a gas in high-pressure apparatus) has a critical influence on the withstand voltage level of the insulating gap. The electric field is calculated using the charge simulation technique at the triple junction as a function of the junction geometry. The dependence of the field is studied for a varying contact angle a between the solid insulator and the electrode in the range 0 to 90°, for a varying ratio r/D of the radius of curvature r of the rounded edge of the solid insulator at the junction to the length of the insulator D, at a fixed r/D and varying r and D and for different practical insulator materials having relative dielectric permittivities ¿£ in the range 2.1 to 12000. It has been found that the electrical field at the electrode-solid insulatorvacuum junction has a strong dependence on both the contact angle and the solid insulator material. The tangential and normal components of the electric fields are determined at the solid insulator-vacuum boundary and away from the boundary both inside the solid insulator and in the vacuum. Large enhancements in the electric field at the triple junction are found. The effects of the parameters ¿, r, and ¿r on the with-stand voltage of the insulating gap are discussed.