Aging phenomenon of 15 kV EPR cable insulation by electrical and thermal stress

Due to high dielectric strength, high resistance to water treeing, and thermal stability, the Ethylene Propylene Rubber (EPR) is an excellent choice for polymeric cable insulation. As for its higher dissipation factor, the usage of EPR materials for power cable insulation is limited to 154 kV. For the typical medium voltage EPR cables, the designed operational electrical stress does not exceed 5 kV/mm. The study in the past revealed that the perfect-manufactured EPR material would not trigger significant aging for the ac electrical field stress less than 20 kV/mm. Yet the failures of medium voltage cables under operational conditions still occurred. In the study, the EPR insulation sliced from 15 kV EPR cables were aged by high electrical stress as well as the thermal stress. The data of time-to-breakdown were collected to extrapolate the life-time model of the tested EPR cable insulation.