Flashover voltage of high-voltage insulators with uniform surface-pollution films

Abstract

Contamination on the surface of high-voltage outdoor insulators can lead to the formation of quasistable gas discharges, which burn in series with the resistive contaminative film. Under certain conditions, these discharges may grow to cause a complete flashover. In this paper, a model for the case of a discharge burning on a rectangular polluted strip is introduced; solution of Laplace's equation in two dimensions enables accurate values for the series resistance of the pollution film to be calculated, and a numerical method is used to calculate a factor which accounts for the change in resistance due to heating. Application of the flashover criterion di/dx>0 to this model yields results which are in good agreement with experiment. The model can also be applied to axisymmetric insulators with complex shapes by replacing the practical insulator by its ‘equivalent cylinder’ Good agreement is obtained between the calculated flashover voltages and those measured by the VDE 0448 test method.