Electric Fields and Composite Insulators

Composite insulators have been applied since the 1970s at transmission voltages for a range of reasons including lower cost, reducing contamination outages and addressing vandalism concerns. The electric field (E-field) distribution along the insulator is an important factor which impacts the life expectancy as high E- field magnitudes can result in a discharge activity which in-turn can damage the insulating material resulting in failure. In order to reduce the high E-fields close to the ends of the insulator corona or grading rings are applied. This panel session paper will present the impact of the E-field distribution on the short and long term performance of composite insulators; how to model the E-field distribution; approaches to design corona rings to manage the Efield distribution; and laboratory testing to evaluate the performance of corona and grading rings.