Evaluating the resistance of power cable insulation to ageing under thermal cycling and over-voltage conditions

Equipment for automatic thermal cycling tests on power cables is described. Temperature measurements on an auxiliary cable carrying the same current, permit the temperature of the test cable to be controled and recorded while high voltage is applied. Preliminary tests on 15 and 25 kV cables with EP rubber insulation show that there was no deterioration after 20 cycles with the conductor at 90°C and at twice rated voltage (2 V0). The loss tangent of the 25 kV cable increased to about 50% over the initial value after 24 cycles at 130°C, but showed no further deterioration after 24 cycles at 150°C (at 3 V0). No significant discharges occurred in the cables after heat cycling.