Merging the electro-thermal life model for power cables with the statistical volume enlargement law

In this paper the combined electro-thermal life model for the insulation of power cables is extended in order to include the volume enlargement law, whereby the statistical breakdown behavior with the increase of insulation volume is accounted for. In this way, a new comprehensive model is obtained, whose usefulness lies in that it includes the effect of volume enlargement - beside that of electrical and thermal stresses - on life estimation. This combination is particularly useful for power cables. Indeed, the extrapolation from laboratory test results to in-field expectations implies a significant enlargement process over cable insulation volume, since life tests are performed using short cable lengths and, furthermore, “mini-cables” most of times. Consequently the estimation of life expectation of a full size cable installed in field cannot disregard the volume enlargement law. In the paper, the novel extended life model is illustrated and discussed considering both AC and DC high voltage power cables.