The results show that in SF6 there is obvious difference between the positive and negative onset voltage and the difference is increased by an increase of gas pressure. However

in air the positive onset voltage are close to the negative ones at a fixed condition. The positive streamer pulses are not alaways random under all conditions

e. g.

the positive streamer pulses are regular in SF6 when the pressure is low enough. In air

the corona stabilization is influenced not only by the change of pressure

but also by the variation of rod electrode tip-radius. The negative breakdown voltage shows a downward decreasing trend with the increasing of tip-radius

yet positive breakdown voltage decreases significantly with the decreasing of tip -radius.