Investigation on electrical performance of semiconducting glazed insulators under natural pollution in Thailand

On economic reasons, high voltage overhead lines are widely utilized for transmitting electrical power for a long distance. In such a way, insulators have to be used as insulating supporters in various environments. In polluted area, the electrical performance of insulators will be degraded. The polluted insulators will have lower withstand voltage, flashover can occur easily when the air becomes wet by very higher humidity or fog, which affects on the reliability of the power system. It is supposed that such problems can be solved by utilizing semiconducting glazed insulators. This paper reports the three years results of experimental investigation on semiconducting glazed insulator exposed in differently polluted areas, in which equivalent salt deposit densities (ESDD) have been known, namely industrial chemical pollution, salt from sea and dust pollution. The investigation was carried out on small long rod insulators with rating at 33 kV. The test samples are porcelain and silicone insulators with leakage distances of 60 cm and 84 cm respectively. The flashover test on natural polluted insulators were performed in a clean fog chamber after the insulator samples had been hung in specified polluted areas for different periods, e.g. 5 month, 8 months, 10 months and 12 months. The investigation was conducted for three years. The tests procedure were performed in accordance with IEC 507-1991. The comparison of flashover voltage results under wet condition with clean fog are made between normal glaze and semiconducting glazed insulators and silicone insulator as well. The results show that flashover voltage of the semiconducting glazed insulators with different kinds of natural pollutions are about 2-3 times higher than of normal glazed insulators and a little bit higher than that of silicone rubber insulators.