Composite rod insulators for AC power lines: electrical performance of various designs at a coastal testing station

The electrical performance of 36 composite insulators comprised of four commercial types for each AC-system level of 34.5 kV, 230 kV, and 500 kV is determined. The weathershed materials are epoxy-resin, ethylene propylene rubber and silicone rubber; half of the 230 kV insulators had no stress rings. Surface leakage current is recorded for surge levels of 25 mA, 150 mA, and 500 mA. A special technique is developed to obtain the flashover statistics of the 500 kV insulators, thereby allowing performance of the composite insulator to be quantified relative to that of a string of cap and pin porcelain insulators of antifog design. The deterioration of the insulators is observed by making regular visual inspections. The practical consequences of the findings and the causes of the degradation are discussed