Discharges in Air from Point Electrodes in the Presence of Dielectric Plates: Theoretical Analysis

This paper investigates the onset of dc corona from a point electrode as influenced by a nearby dielectric plate as well as the charging of the plate by the corona space charge. The electric field in the vicinity of the point is influenced by surface charges building up on the dielectric plate during voltage application. The field is calculated using the charge simulation technique where the electrodes are simulated by discrete charges and the dielectric plate by area charges. The potential and field in the vicinity of the stressed electrode as well as the maximum surface charge on the dielectric plate are determined by applying suitable boundary conditions during voltage application. The distribution of surface charge on the dielectric plate is measured by means of an electrometer with a specially designed electrostatic probe. The calculated onset voltages and surface charge distributions are compared with those measured experimentally.