Life-time characteristics of EPR cable insulation under electrical and thermal stresses

Ethylene Propylene Rubber (EPR) has been used as the insulation for polymeric power cables for its good dielectric properties. For the typical medium voltage EPR cables, the designing electrical stress should not exceed 5 kV/mm under normal operational conditions. The majority of the EPR cables have a maximum working temperature of 105 °C with the capability of working at 140 °C for short-time period. Since the occasional over-voltage and over-current will accelerate the aging, it will be necessary to determine the life-time characteristics under the combined high electrical and thermal stress. In the study, EPR cable insulation samples of 90 μm thick were sliced from the commercial-available 15 kV EPR cable. Constant ac voltage was applied to the cable samples while the test temperature was kept at 105 °C, 140 °C, 165 °C, and 190 °C accordingly. The time-to-breakdown data were collected to extrapolate the lifetime characteristics of the tested EPR insulation samples.