This paper describes theoretical and experimental investigations of the effect
of an electrode coating on the onset voltage of a corona on negatively
stressed electrodes. Dielectric-coated hemispherically-capped rod-to-plane
gaps positioned in air are investigated. The onset voltage is calculated
based on the self-recurring single electron avalanche developed in the
investigated gap. Accurate calculation of the electric field in the vicinity of a
coated rod and its correlation to the field values near a bare rod of the same
radius are obtained using the charge simulation method. The calculated field
values are utilized in evaluating the onset voltage of the corona. Also,
laboratory measurements of the onset voltage on bare and coated electrodes
are carried out. The effects of varying the field nonuniformity, the coating
thickness and its permittivity on the onset voltage values are investigated.
The results show that coating the electrodes with a dielectric material is
effective in increasing the onset voltage of the corona on its surface. The
calculated onset voltage values for coated and bare electrodes agree
satisfactorily with those measured experimentally.