Space charge distribution measurements in XLPE and EPR

The Thermal Step Method was employed to determine the space charge distribution in cross-linked polyethylene (XLPE) and ethylene propylene rubber (EPR) aged in dry and wet environments, while the amount of charge in the polymer was determined by the Thermally Stimulated Discharge Current technique. It is shown that these two techniques complement one another. To simulate the insulation used in underground high voltage cables the polymeric insulation was sandwiched between two semicon electrodes. When subjected to DC voltage in a dry environment, EPR insulation accumulates significantly more space charge than XLPE insulation. AC aging under wet condition produced few water trees in XLPE and EPR but negligible quantities of space charge in both types of insulation. No correlation could be established between the amount and distribution of space charge and the length of water trees