Effect of Epoxy Resin Spacers on Corona Characteristics in SF6/N Mixtures under Positive DC Voltages

Insulator is a very typical weak point of inner insulation in gas-insulated power equipment, which is commonly made of alumina-filled epoxy resin. When a corona discharge is caused by tip defect near the insulator, it may lead to the corona develop into a surface discharge, resulting in insulation degradation. In this paper, we investigate the effect of epoxy resin spacers on corona characteristics in SF6/N(5:95) mixtures under positive DC voltages. A three-electrode arrangement corona discharge experimental platform was built. For a constant electrode gap spacing, the influence of tip defect location on corona characteristics is analyzed by using the same size epoxy resin spacers. Characteristics of corona were studied including the corona onset voltage, breakdown voltage, current pulse, and changes in corona pattern. The experimental results have shown that the corona onset voltage and breakdown voltage increase first and then saturate with increasing distance between the needle electrode and the dielectric surface. The corona pulse characteristics are not affected by dielectric solid. If the needle electrode is located at the surface of the epoxy resin spacer, the corona will be attracted to the dielectric surface, forming so called surface discharge. If the needle electrode is set away from the surface, corona discharge will also be attracted by the surface and form a 'towards dielectric' component. But the surface effect decreases with increasing distance, in our case, the dielectric effect can be neglected if the distance is larger than 12 mm.