Polarity effect in DC withstand voltages of contaminated surfaces

The characteristics of partial arcs on contaminated surfaces are believed to dominate the withstand voltage of a contaminated insulator. The structure of a DC partial arc on an experimental model of an insulator surface contaminated with sodium chloride is investigated using a still camera and an interferometric method. The results reveal a difference in the structure of the positive and the negative partial arcs, and make it possible to explain the cause of the polarity effect in the withstand voltage of a heavily contaminated DC insulator, namely, the negative withstand voltage is lower than the positive. It is concluded that knowledge of the structure of partial arcs can be used in constructing an advanced mathematical model of the flashover phenomenon on a contaminated surface.<
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