Study of ac pollution flashover performance of porcelain insulators at high altitude sites of 2800 ~ 4500 m

The external insulation of electric equipments will be affected by the atmospheric conditions in the high altitude regions. However, a few investigations at the high altitude sites of 3000 m and above have been conducted. This paper reports on the laboratory tests of artificially polluted cap-and-pin porcelain insulators performed at the high altitudes of 2800 m to 4500 m. The test results and analysis show that the pollution flashover voltages in high altitude regions are affected not only by the pollution grades but also by the atmospheric parameters. The exponent characterizing the influence of equivalent salt deposit density is 0.26 to 0.29 and the one characterizing the influence of nonsoluble deposit density is 0.09 to 0.15. The ac pollution flashover voltage UF will decrease with the decrease of air pressure P and increase with the decrease of ambient temperature t. [U.sub.f] is a power function of the ration of air pressure P/[P.sub.o] and also is a power function of the ambient temperature coefficient (1 + 0.02(t - 20)). The average exponent characterizing the influence of air pressure is about 0.56 and the exponent characterizing the influence of ambient temperature is about 0.21 for the three types of insulators in the paper. Index Terms--AC insulator, atmospheric parameter, flashover, high altitude site, pollution grade.