Identification of AC Electro-thermal Ageing Markers from Artemis Cable Peelings.

XLPE cable peelings taken from underground High-Voltage cables that had previously been stressed under different ac electro-thermal conditions are investigated, with the aim of identifying properties indicative of the changes brought about by ageing. The inherent endurance ability of these peelings has been tested for three different endurance conditions of high ac electrical and thermal stresses. Space charge measurements via Pulse-Electro-Acoustic and Thermally-Stimulated-Currents are utilised to evaluate the state of the peelings before and after the endurance test in comparison with unstressed material. It was found that the pre-stressing altered the inherent endurance capability of the peelings especially for materials that had experienced thermal and electro-thermal stressing as a cable. The space charge behaviour also showed changes due to the stressing, related to the accumulation and transport of charge, with ac-electrical stressing reducing the time for heterocharge accumulation at the anode and AC electro-thermal stressing facilitating positive charge injection and propagation to the cathode. A double positive peak near one electrode was identified as indicative of irreversible degradation.