Investigation of thrasher compression fittings on BPA´s direct current transmission line

An attempt was made to predict thrasher fittings´ future performance and develop a reinforcement design. Fitting test data, field experience, and design parameters were correlated into an analytical tool, Bennett number, capable of ranking relative fitting performance. Bennett number also has potential as a design tool for establishing minimum fitting diameter and electrical size. Bennett number, laboratory data, and field experience were used to identify the thrasher fittings and five other fitting designs used at BPA as suspected or demonstrated marginal performers over their design lives. The thrasher fittings could exhibit unacceptable performance before the end of their expected life. Based on laboratory tests, the thrasher fittings have an estimated remaining life of approximately 30 years. It is concluded that the best way to mitigate a failed or marginal thrasher fitting is by reinforcement. The reinforcement design is a helical shunt which acts both as a current shunt and heat shed enhancer