Accelerated aging of TRXLPE insulated cables using water-filled tanks

Accelerated aging tests were performed under controlled conditions on 15 kV rated cables insulated with a water tree retardant cross-linked polyethylene (TRXLPE) insulation. Two test schemes were followed: (1) time-to-failure test, in which cables were aged to failure in tanks and the failure data was statistically analyzed; and (2) fixed time aging in which groups of five cables were aged for each fixed time period (120, 240, 420, 600 days) under a given condition subsequent to which AC electrical breakdown strength of the aged cables was measured to assess the insulation degradation. The effect of aging temperature on the time-to-failure and the effect of aging time on the AC breakdown strength of the TRXLPE insulated cables are discussed in this paper. The water tree growth characteristics of the TRXLPE insulation after aging under different conditions are compared and correlated to the stability in its AC breakdown strength. It is shown that fixed time aging using water-filled tanks is complimentary to the most widely used life tests. The scope of using these tank tests to differentiate XLPE and TRXLPE insulated cables is also discussed.