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 cross-linked polyethylene samples submitted to dc 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 onset of space charge accumulation. The two techniques give therefore consistent information on space charge phenomena and associated energy release in the optical EM spectrum.