HVDC wall bushing performance in wet weather

There is a history of flashovers of wall bushings in rain, even when they are relatively clean. These flashovers appear to be associated generally with a non- uniform rain distribution because of the shielding effect of the valve hall. This paper reports that a study has been made of this problem involving the development of laboratory test techniques to simulate the critical conditions, and also verification that the rapid flashover clean fog test can be used for evaluating a polluted DC bushing. Using these techniques a conventional bushing has been assessed and a method of improving its performance has been found by fitting it with supplementary silicone-rubber sheds, (booster sheds). The effects of various numbers of such sheds on the bushing have been measured, as have the effects of modifications to the booster shed.