On the design, testing and operating experience of composite dry bushings in HVDC

As part of the ongoing attempts to solve the external flashover problem of HVDC wall bushings, Manitoba Hydro installed a 500 kV composite dry wall bushing with hydrophobic silicone rubber sheds. The bushing was installed in the negative pole (-500 kV) on the valve winding side of the high voltage converter group at the inverter (Dorsey Station). It was found that the external flashover performance of composite dry bushings without any additional corrective measures is as good as conventional porcelain bushings, which are either equipped with booster sheds or coated with any type of protective coating. This performance has been demonstrated under clean fog and nonuniform rain conditions. The silicone rubber sheds are durable. The elimination of oil from the design eliminates a major fire hazard