Laboratory tests to evaluate HVDC wall bushing performance in wet weather

Two test methods are developed to simulate the conditions causing flashover of DC wall bushings at working voltage. One is based on the clean-fog pollution test. The other is a rain test, with part of the bushing unwetted. The effect of varying test parameters is measured and five variants of rain test are adopted for measuring the performance of a wall bushing. Its performance compared unfavorably with that of an empty porcelain shell. Various numbers of booster sheds (removable silicone-rubber cones fitted round the bushing) are found to improve its performance substantially