Aging of dielectric liquid-impregnated-paper insulated bushings under voltage switching surges

Aging studies have been carried out on dielectric liquid-impregnated-paper insulated bushings subjected to voltage switching surges. The rate of deterioration of the insulating system of the bushings increased with the number of the switching surges applied. The extent of aging or deterioration of the insulating system was manifest by a decrease in the partial discharge inception voltage and an increase in the cumulative apparent charge transfer. An improvement in the partial discharge characteristics was observed when the bushing specimen was allowed to remain under stress-free conditions for an extended period of time prior to the application of the subsequent series of repetitive impulses.