Effect of saline Deposition and Surface Flashover on High Voltage Insulators in Coastal Areas

Pollution flashover is one of the major factors affecting the design of external insulators to provide a reliable and secure operation of transmission lines. There have been many studies and research on the flashover mechanism of polluted insulators in several countries. However, because of the complexity of the flashover mechanism and dependency on factors such as climate conditions, environmental stresses and pollutants in various areas, the pollution flashover incidents still occur frequently, therefore more research is needed to investigate these incidents. Up to now, the research mainly focused on the polluted insulators with ice and snow to determine the surface flashover and they barely touched the cold-fog method to investigate the surface flashover process on polluted insulators. In winter and early spring, due to the combined effect of saline and cold fog deposition, leakage current (LC) flows on the insulators and surface degradation may take place, which cause an increase in leakage current and dry bands formation on insulator surface, finally the partial arcs occur across the dry bands. As the partial discharges increases the individual partial arcs become connected and complete flashover occurs. The performance of the polluted insulators mainly depends on the conductivity of the polluted surface layer which can be determined from the equivalent salt deposited density of the polluted surface layer. The main objective of this research was to investigate the flashover phenomenon on high voltage polluted insulators by measuring and calculating several important flashover processes with the combined effect of saline deposition and cold fog. Two contamination categories were considered: Uniform and non-uniform surfaces for measurements. For uniform contamination, the method described in [4] was adopted. Investigation has been carried out on different stages of flashover i.e initial stage, intermittence local arc stage, arc propagation stage, critical flashover stage and flashover stage, also the impact of wind, rate of saline accumulation on high voltage insulators under cold fog and different environmental stresses were studied.