Space charge accumulation and conduction current in XLPE insulation

Space charge and conduction current measurements have been performed on XLPE insulation with semiconducting electrodes subjected to dc electrical fields between 20 and 70 kV/mm. It was found that the space charge accumulation in fresh insulation resulted in heterocharge distributions, which was attributed to the presence of curing by-products. In degassed insulation, the space charge accumulation resulted in homocharge distributions for the lower charging fields and an additional heterocharge accumulated near the cathode for the higher charging fields. The modification of the electrode electrical fields in degassed XLPE was found to be approximately half of that in fresh XLPE. On basis of conduction current measurements in degassed XLPE it was difficult to identify the controlling conduction mechanism(s) and to establish a clear correlation between the conduction current and space charge accumulation.