Comparison of pollution flashover performance of porcelain long rod, disc type, and composite UHVDC insulators at high altitudes

Aiming at porcelain long rod, disc type and composite long rod UHVDC insulators, this paper presents a comparison of their dc pollution flashover performances and an analysis of arcing behavior at high altitudes (1970m). The solid layer method was used in artificial pollution tests, in which sodium chloride and kaolin powder were used to simulate conductive and inert materials. The insulators were wetted by steam fog in a fog chamber. The 50% flashover voltage (U
_50%
) was measured with the up-and-down method. According to the test results, the three types of insulators are similar in the characteristic exponent which characterizes influence of the salt deposit density on the flashover voltage. Due to lower utilization ratio of leakage distances, pollution flashover voltage gradient for the porcelain long rod insulators is lower than that for the disc type insulators. Whereas covered with Room Temperature Vulcanized (RTV) silicone rubber coatings on the trunk surfaces, the porcelain long rod insulator is much superior to the disc type insulators in pollution flashover voltage gradient. The dc pollution flashover performance and the utilization ratio of leakage distances for the composite long rod insulators are much better than those for the other two types of insulators, which are induced by the special configuration of composite long rod insulators.