Impulse corona in positive rod-plane gaps filled with SF6 gas mixtures

Breakdown and corona inception voltages were measured for SF6, N2 mixtures using rod-plane gaps and positive impulse applied voltage. The results are in general agreement with previously publisbed reports. Corona discharges in these gases were also investigated The results indicate that in N2, streamer type corona exists. In SF6 - N2 mixtures with ≥ 1% of SF6 content, streamer type corona exists from 0.5 to 1 bar, whereas leader /streamer corona appears at pressure of 1. At high pressures, this type of corona results into a direct breakdown. In general, this type of corona extends into the gap in a stepped manner. The range of streamers, the size of the leader step and the time between leader steps decrease when SF6 content and/or gas pressure is increased. At law pressures (0.5 bars) in some mixtures (80% SF6) a pseudo glow/streamer type corona is observed.