Space charge behavior at physical interfaces in cross-linked polyethylene under DC field

Space charge behavior at physical interfaces in cross-linked polyethylene (XLPE) films subjected to a dc field has been investigated as a function of the nature of the interfaces using the pulsed electro-acoustic technique. Aluminum, gold and carbon black-loaded polyethylene were used as electrodes to investigate space charge build-up in a single dielectric layer. A sandwich structure constituted by two dielectric films of the same nature was used to study the charging propensity of the dielectric/dielectric interface. Samples with uncharged and charged interfaces were investigated. The time dependence of the space charge distribution was subsequently recorded at different temperatures under field (polarization) and short circuit conditions (depolarization). Charge injection rather than ionic species migration is seen to control space charge distribution in single and double- layer samples in agreement with the storage conditions of the XLPE films. It is shown that the sign and distribution of the space charge depend drastically on the nature and the polarity of the electrodes and that dielectric/dielectric interfaces behave differently depending on the sign of the charge, providing deeper traps for positive charge carriers.