The barrier effect on the onset voltage of negative corona in air

Abstract

This paper is aimed at calculating the onset voltage of negative corona in rod - plane gaps as influenced by the presence of a dielectric barrier located either parallel or normal to the gap axis. The effect of the barrier thickness, permittivity and location with respect to the stressed rod on the calculated onset voltage is investigated. The method of calculation is based on the criterion of self-recurring single electron avalanches developed in the gap when stressed negatively. The electric field values used for avalanche growth are evaluated using a combined technique based on boundary-element and discrete-charge simulations. In this technique, the surface charge on the rod is simulated by fictitious discrete charges while the surface charge on the faces of the barrier is simulated by surface charged boundary elements. The electric field assumes values higher than those in the absence of the barrier whatever the position of the barrier, parallel or normal to the gap axis. The smaller the distance between the barrier and the rod, the larger the thickness and the higher the relative permittivity of the barrier, the lower is the corona onset voltage.