Flashover performance of non-uniformly polluted glass insulating surface under HVAC stress

This paper examines the performance of polluted insulating surfaces with non-uniformly distributed pollution. An experimental study simulating insulator samples contaminated with pollution layers of different pollution severity and dimensions on their surface is carried out. The pollution repartition includes configurations consisting of adjacent layers of contrasting conductivity values, with the position and the length of the layer having high conductivity being varied within the electrode gap distance. The voltage applied to the test electrode gap is increased within a range of values below the flashover voltage. For each voltage level and pollution configuration, the discharge characteristics are obtained by analysing the leakage current, the arc length and the flashover voltage. Based on an equivalent electrical circuit, a mathematical model that considers non-uniform pollution conditions is proposed. The model allows the determination of the main parameters characterizing the discharge propagation up to flashover: the critical arc length, the critical leakage current and the critical flashover voltage. The computed model predictions are validated with experimental results, and a very good agreement was obtained. It is expected that the proposed study brings a useful contribution into the understanding of insulator flashover subject to more realistic, non-uniform distribution of contaminants on the surface.