Theory of positive onset corona pulses in SF6

The mechanism of formation of positive corona onset pulses in SF ₆ at 100 kPa is examined. A constant positive voltage of 50 kV is applied to an 0.5-cm diameter sphere located 6.5 cm from a grounded plane. The calculated current pulse has a width at half maximum amplitude of ~0.3 ns, thus explaining the origin of subnanosecond current pulses in SF₆. During the current pulse a streamer moves out into the gap along a 100-μm channel, with the electric field in the streamer trail E>E*, where E* is the critical field for which ionization equals attachment