Characteristics of Surface Discharge with Small Gap in SF₆ Gas under Pulse Voltage

Abstract

The barrier effect of the corona and surface discharge characteristics of SF₆ and mixture (SF₆+N₂), in high-field needle to plane gaps with short gap length, was examined under negative polarity pulse voltages with various wave fronts. At constant gap length in SF₆ gas, the discharge voltage increased with the barrier height. And also the discharge voltage increased with increasing the wave fronts in the μs region. On the other hand, under same barrier condition in N₂ gas the discharge voltage decreased with increasing the wave fronts. In order to make clear the mechanism of corona initiated surface discharge, the charge magnitude on the barrier induced with the corona was measured by a electrostatic voltmeter. The charge density was approximately 4×10^-4C/m² at 0.1Mpa and 15kV. The corona properties under various pulse wave fronts were observed with an optical technique such as an image intensifier tube. Anomalous V-t curves obtained in SF₆ gas are considered to arise from the relaxation of electric field resulting from the influence of charge accumulated on the barrier due to corona at wave front of applied pulse.