COMPOSITE ROD INSULATORS FOR AC POWER-LINES - ELECTRICAL PERFORMANCE OF VARIOUS DESIGNS AT A COASTAL TESTING STATION

The electrical performance of thirty-six composite insulators - of four commercial types for each AC system level of 34.5 kV, 230 kV and 500 kV — has been determined at the CEGB Insulator Testing Station, Brighton on the south coast of England. The weathershed materials were epoxy-resin, ethylene propylene rubber and silicone rubber; half of the 230 kV insulators had no stress rings. Surface leakage current was recorded for surge levels of 25 mA, 150 mA and 500 mA; a special technique was developed to obtain the flashover statistics of the 500 kV insulators, thereby enabling performance of the composite insulator to be quantified relative to that of a string of cap and pin porcelain insulators of anti-fog design. The deterioration of the insulators was observed by making regular visual inspections. The practical consequences of the findings and the causes of the degradation are discussed. © 1990 IEEE