Effects of pollution materials on the AC flashover performance of suspension insulators

The type of pollution materials may influence the flashover performance of an insulator. In this paper the pollution flashover performance of a 7-unit insulator string, consisting of typical discs, is determined by laboratory tests while varying the weight percentage of soluble (NaCl and CaSO₄) or non-soluble (SiO₂, Al₂O₃ and Fe₂O₃) materials. When studying the effect of pollution materials on flashover performance, the influence of volume conductivity and equivalent salt deposit density (ESDD) under different weight percentages of soluble materials is firstly investigated, and then the underlying factor, the thermal ionization of pollution materials, is considered. Finally, the measurement results of leakage current under different pollution materials are presented. The research results indicate that the effect by weight of CaSO₄ is not as severe as that of NaCl, and the reason is not just its effect on the layer conductivity and ESDD, but its effect on the thermal ionization during the arc propagation process may also be one of the key factors. The fact that a small amount of Al₂O₃ and Fe₂O₃ causes the flashover voltage to decrease by 20%, may result from the lower ionization potentials and the higher leakage currents caused by non-soluble materials containing Al₂O³ and Fe₂O₃.