Environmental effects on the rate of aging of EP insulated power cable

The accurate prediction of service life of extruded dielectric power cables from relatively short term laboratory tests has been and continues to be, a challenge for power cable engineers. Incomplete understanding of failure mechanisms and the effect of the many different in-service environmental factors, possible interactions between these factors, and the widely scattered nature of dielectric phenomena contribute to the uncertainties. In this laboratory investigation of the effects of water, water temperature, air temperature, voltage impulses, current loading and their interactions on a shielded 5 kV ethylene propylene rubber (EP) insulated power cable, water and water temperature were found to have the largest effect on dielectric strength. When aged in air for 3 years at 4.5 times rated voltage (the least harmful condition found in the experiment) the average dielectric strength declined to 92% of the original value, however this decline is not statistically significant. When aged in 35°C water for 3 years at 4.5 times rated voltage (the most harmful condition found in the experiment) the dielectric strength declined to 21% of the original value.