Life model based on space-charge quantities for HVDC polymeric cables subjected to voltage-polarity inversions

This paper illustrates a new model that enables the estimation of life of polymeric insulation subjected to DC stress, both in the presence and in the absence of voltage polarity inversions. The derivation of the model parameters is based on the results of space charge measurements and accelerated life tests realized at constant DC stress, which allows the characterization of the performance of insulating materials under DC electrical stress to be carried out in short times. The expected life of a cable in service can be evaluated by means of this model, provided that the rate of voltage inversions expected during its life is known or estimated. The model is applied here to results of tests carried out on polyethylene-based materials for cable insulation, and model parameters are calculated resorting to two different approaches. A satisfactory fitting of life test results is achieved, thus confirming the validity of the proposed model.