Effect of Surface Charge Control on DC Corona Onset Voltages

Abstract

A dielectric disc with a thickness of 0.1 cm placed on the plane electrode in a rod to plane room air gap of 2 cm long is charged by DC corona discharges with the positive and negative polarities. The dielectric discs made of acryl PMMA have six kinds of radii from 2 to 16 cm. The surface potentials induced from the accumulated surface charges are measured by a vibrating capaciting voltage meter which can be controlled in the direction of X and Y, and the effect of surface potential on the corona onset voltage is also investigated from both the laser-induced measurement of electric field and the theoretical calculation of surface potential and electric field.In order to make clear the effect of surface charge on the corona onset voltage under the same gap condition, we measure the onset voltage by using the applied voltage of same or inversed polarity to the polarity of surface charge just after the charge deposition was achieved on the dielectric disc. In the case of same polarity, the corona onset voltages increase with increasing the amount of surface charge. However, in the case of inverse polarity the corona onset voltages remarkably decrease in increase of the amount of the charge and are much lower than those without the surface charge. Also, it is surprising that in spite of short gap length 2 cm, the charging area spreads more than that with a radius of 16 cm around the disc center.