Space charge and associated electroluminescence processes in XLPE cable peelings

The intent of this paper is to cross-correlate the information obtained by space charge profile analysis and electroluminescence (EL) detection in crass-linked polyethylene samples submitted to de fields, with the objective to make a link between space charge phenomena and energy release as revealed by detection of visible photons. Space charge measurements carried out at different electrical fields by the pulsed electro-acoustic method show the presence of a low-field threshold, close to 15 to 20 kV/mm, above which space charge begins to accumulate considerably in the insulation. Charges are seen to cross the insulation thickness through a packet-like behavior at higher fields, starting at about 60 to 70 kV/mm. EL measurements show the existence of two distinct thresholds, one related to the permanent excitation of EL under voltage, the other being transient EL detected upon specimen short-circuit. The former occurs at values of field corresponding to space charge packet formation, and the latter to the on-set of space charge accumulation. The two techniques give therefore consistent information on space charge phenomena and associated energy release in the optical EM spectrum.