The performance of HVDC wall bushings with silicone rubber sheds

Until late 80s, most of the HVDC wall bushings installed, including those at the DC voltage of 600 kV, were provided with porcelain insulators with glazed external surface. During 70s to 80s, large numbers of flashover incidents have been reported on HVDC wall bushings. Many studies have been carried out on this problem. Uneven wetting, as the main cause of those flashovers had been identified and effective remedy methods have been introduced. However, the effects of those incidents on the design criteria for external insulation can be observed even today. Since late 80s, HVDC wall bushings with silicone rubber sheds started to be installed in HVDC stations. Since then, most of HVDC wall bushings installed, at various DC voltage level up to 800 kV, have been with silicone rubber sheds. Good operation experiences have been reported. In this paper, firstly, a revisit of the conclusions obtained regarding the performance of wall bushings with porcelain sheds will be made with special attention to the related design criteria and test requirement. Following that, a review of the performance of wall bushings with silicone rubber sheds is made also with special attention to the related design criteria and test requirement. Conclusions and recommendations will be given.