Effect of long-time electrical and thermal stresses upon the endurance capability of cable insulation material

This paper presents the results of endurance tests that have been carried out on cross-linked polyethylene (XLPE) cable peelings. The peelings were taken from cables that were manufactured from a single batch of XLPE and subjected to electrical (up to 28 kV/mm), thermal T = 363 K (90degC) and electro-thermal stressing for at least 5000 hours. The endurance tests of the peelings (thickness 150 mum) were carried out at the same temperature of T = 363 K as the thermally stressed cable, but at two different AC electrical fields of 55 and 70 kV/mm. The resulting life data for the different sample sets are compared to one another and to that of peelings taken from unaged cables. Weibull analysis of the failures shows that only peelings from cables that had experienced a thermal stress component during their time of stressing as a cable, exhibited a statistically significant reduction in endurance capability. Possible reasons for this reduction of life are discussed.