Theory of discharges in air-filled insulation voids

An initial seed electron, in an air-filled void in an insulator, is followed until a Gaussian shaped electron avalanche is formed that eventually distorts the electric field to form both cathode and anode directed streamers. The crucial role of photoionisation in the three-dimensional formation of a streamer discharge in a void, is demonstrated by performing calculations both with and without a three-dimensional treatment of photoionisation. The calculation is not constrained in any way, so that the shape of the discharge is determined as a solution of the fundamental equations