An artificial pollution test on silicone rubber insulators under long-time wetted conditions

Currently, the pollution performance of silicone rubber (SIR) insulators is mainly evaluated by the clean fog test method, in which the wetting time of a tested sample is kept within 1 to 2 hours. The objective of this paper is to validate if it is necessary to take the longer wetting time than 2 hours for SIR insulators in the clean fog test. A type of kieselguhr-polluted SIR insulators with the strong surface hydrophobicity was evaluated in a unique environmental test chamber. Each insulator was tested for 24 hours or until a flashover occurred. The test results show that it took 8 hours to 14 hours for some tested insulators to flash over at the scheduled levels of high voltages, due to the gradual decrease in surface hydrophobicity and the consequential increase in wettability with time under the fog conditions. However, the leakage current along the insulator surfaces had no remarkable development before the flashover occurred. The test results prove that it is necessary to take much more wetting time than 2 hours to evaluate the flashover performance of SIR insulators in the clean fog test. Furthermore, another test on the kaolin-polluted SIR insulators with the weak surface hydrophobicity indicated that in order to obtain the lowest pollution flashover voltages of SIR insulators under longtime wetting conditions, the fog parameters should be reasonably chosen to avoid the heavy lose of the salt density on the insulator surfaces with time.