The influence of surface charge on lightning impulse breakdown of spacers in SF/sub 6/

We have investigated the influence of surface charges on the discharge development across particle contaminated spacer surfaces under SF/sub 6/ for lightning impulse (LI) voltages (1.2/50 /spl mu/s). Surface charges may be generated by dc, ac or lightning impulse stress. The discharge characteristic shows a strong reduction of the insulation strength if the applied voltage and the surface charge have opposite polarities. The investigations were performed with a needle protrusion attached to the bottom electrode to give severe field distortion. The bottom electrode was biased positively. The influence on the discharge process is observed by measuring the surface charge distribution and predischarge currents. The results reveal changes in streamer onset voltage, streamer to leader transition, and leader development.