A Comparative Study of Polymer Insulating Materials Undern Salt-Fog Conditions

This paper describes the performance of the widely used polymeric insulating materials for outdoor insulation - high temperature vulcanized (HTV) silicone rubber, ethylene-propylene rubber (EPR) and epoxy resins with a commonly used inorganic filler, alumina trihydrate, under salt-fog conditions. The role of the filler and the effect of the filler concentration in imparting track resistance to the materials is investigated. Various methods to describe the surface aging of polymer materials such as the peak and the average of the leakage current, the cumulative charge, the weight loss and the flashover voltage have been investigated. The results show that at moderate concentrations of filler, 105 to 130 parts per hundred (pph) of polymer, there is little difference in the performance of silicone rubber and EPR materials. At low concentrations of filler (30 pph), the EPR samples track whereas the silicone rubber samples erode. The epoxy materials exhibit inferior properties when compared to silicone rubber and EPR. The results also indicate that monitoring the weight loss, the reduction of the flashover voltage, and the peak of the leakage current are better methods to characterize aging of insulators than the average of the leakage current or the cumulative charge.