Electric Field Distribution at Solid Insulator-Vacuum Interface of Different Electrode-Insulator Geometries

The distribution of the electric field at the interface of eight different electrode-insulator geometries used in the design of high voltage systems is calculated using the charge simulation technique. The insulators investigated have (1) a metal insert, (2) a recessed electrode, (3) a concave edge, and (4) a convex edge. These four shapes are chosen to occur at (a) both the anode and the cathode junctions (symmetric electrode junctions) and (b) only at the cathode junction (asymmetric electrode junctions). The computed results with symmetric electrode junctions show that the tangential field value at the electrode junctions are lower than the average applied field except in the case of the insulator with a convex edge at both ends. In this case, the field value is higher at the electrode junctions. The use of asymmetric electrode junctions alters the maximum value of the field in the gap and the field at the anode junction; the field at the cathode junction does not show much variation. The influence of the permittivity of the dielectric material on the interfacial electric field is investigated and found to depend on the electrode-insulator geometry. Epoxy (¿2=3.6), Pyrex glass (¿2=4.6) and porcelain (¿2= 10.0) are used. Measurements of the withstand voltage of insulating gaps have been carried out on different electrode-insulator geometries to verify the calculations. Good qualitative agreement is obtained.