Simulation of corona discharge. Negative corona in SF6

Negative coronas in SF₆ under three voltage levels are investigated by Monte Carlo simulation. For the purpose of simulation, the gap between a hyperboloidal needle and a plane is divided into two regions: region I where the electric field is very steep and most electrons and ions are accumulated, and region II the rest of the gap. In region I electron motion is simulated by dividing the region into a number of cells and a small cell size improves the accuracy. The magnitude of current pulse increases with increasing voltage and there appears to be more than one peak in each pulse as observed by experiment. The development of electron avalanches is due to ionization and photoionization in the high field region, while the quenching of the avalanches is due to the space charge field suppression. Also the accumulation of positive and negative ions are displayed in detail. The space charge field distortion is studied and found to increase with increasing applied voltage