Aging and life models for insulation systems based on PD detection

Aging and life models based on growth of electrical trees in insulating materials and systems subjected to electrical stress are investigated. The models consider aging to be primarily a function of either the tree length or the intensity of discharges occurring within the trees. In terms of the latter quantity, a model is postulated, which relates electrical stress, apparent charge and time to end point, i.e. the time needed to reach a limit amount of charge above which the insulation system fails to fulfil serviceability requirements. Generalised probability models are also proposed, which satisfy the need to resort to stochastic considerations for failure evaluation. Even if, in principle, the models hold in the presence of a predominant tree occurring in the insulation, they also can be applied for general purposes from a phenomenological point of view