Effect of the development of electrical parallel discharges on performance of polluted insulators under DC voltage

Our work consists of studying the development of parallel discharges on a broad insulating surface simultaneously under uniform pollution´s conditions and DC voltage. This phenomenon plays a very important role on the electric performance of this insulation. The parameters of influence considered in this paper are the following: the width of the polluted material, the degree of its contamination and the polarity of the applied voltage. The tests were performed on a rectangular surface of a glass with various dimensions, and various types of electrodes (rods, planes) were used. The visualization of the parallel discharges was performed by a fast camera. The experimental results emanated from this study show that there is a limiting band width of pollution from which two consecutive electric arcs can develop independently until the insulation´s flashover with a minimal voltage. The value of this limiting width is approximately 12 cm in positive polarity and 20 cm in negative polarity. It was noted that this limiting effective width is not influenced at all by the variation of the wet layer´s volume conductivity. In this paper, two methods and empirical equation were used to confirm these results. In addition, the results indicate that any plane-plane system of electrodes can be associated with multiple rods-rods configurations, which have the same performance.