Some Physical Properties of Electrical Discharges on Contaminated-Surfaces

The various discharge phenomena caused by contamination of insulator surfaces were investigated by means of slow and fast oscillographic recordings of the discharge current. It was found that the surface discharges have distinct stages of development. The visual manifestations were recorded simultaneously with the current pulses, providing a good correlation and an exact physical interpretation. It was found that contaminated surface discharges can be classified in three main types: the arc, streamer, and glow. The arc discharge has a highly ionized plasma channel with a small voltage drop while the other two are of low ionization density and carry a relatively high voltage. The ignition mechanism was also investigated and explained. Both streamer and glow discharges are accompanied by steep current pulses and are believed to be responsible for the high-intensity radio noise associated with contaminated surface currents. The use of such pulses or bursts of current to evaluate insulator performance is critically discussed.