Electric field distortion at outdoor insulation in severe environments

Summary

In heavily polluted moist conditions, the withstand voltage of outdoor insulation is so severely compromised that a five-fold increase of surface creepage distance is recommended. This is caused by the formation of dry bands in the pollution layer as a result of leakage current, and it has recently been demonstrated that streamer discharges bridge these bands. These not only sustain the bands but also lead to the initiation of the partial arcs which always precede flashover. The distortion of the electric field at the insulator associated with these processes is examined in this paper. This progress has become feasible by the measurement of surface temperature profiles, using infrared video recording, and simultaneous leakage current data of insulator tests in a fog chamber. Analysis of these profiles, together with new thermal modelling of a heat loss coefficient that includes evaporation, enables the resultant electric field in the pre-flashover regime to be quantified.

Additional informations

Authors

Pretorius, Pieter, Rickmann Johannes, Elg Alf-Peter