Breakdown strength of TRXLPE insulated cables after extended aging under moderate test conditions

Accelerated aging of 15 kV cables under moderate test conditions were carried out for extended periods of time. Two test conditions were used to age two TRXLPE insulated cables: (1) aging in water-filled conduits as described in AEIC CS5-94 for a test duration of 600 days, (2) aging in water-filled tanks as per IEEE P1407. It has been shown by these controlled comparative tests that the breakdown strength of TRXLPE1 is very stable over extended periods of aging under both conditions. Test cable failures were recorded during aging of TRXLPE2 insulated cables per IEEE P1407, although the actual value of the breakdown strength and its percentage retention over the unaged reference for some aging time intervals were greater than those for TRXLPE1 cables. This demonstrates that the value of AC breakdown strength at a given point in any aging scheme is not necessarily a true predictor of the performance of TRXLPE insulation. The mechanism of electrical breakdown at elevated stress under ramp tests can be vastly different from the breakdown at constant aging stress