Impulse creeping discharge along the surface of polyethylene wire immersed in transformer oil

The experimental study was performed to clarify the basic behaviour of streamers traveling over the surface of oil-immersed polyethylene insulated wire under a standard lightning impulse voltage application. The effect of the grounded side electrode on the characteristics of creepage discharges, such as discharge inception voltage, discharge extension length, discharge current and charge, discharge figure has been studied. There is a remarkable difference in these characteristics between positive and negative polarities of the streamer. Though the approach of the grounded side electrode to the wire restrains the generation and progression of streamers, it leads to the reduction of a punch-through breakdown voltage of the wire insulator. The authors also measured the electric potential along the streamer channel and the streamer propagation velocity by means of a capacitive probe. It is indicated that the streamer continues to progress in a constant velocity and the streamer channel is not equipotential. The propagation of streamers appears to be stopped by a finite potential drop along the streamer channel