Dielectric Interfaces in DC Constructions: Space Charge and Polarization Phenomena

Interfaces between dielectrics are considered one of the weakest parts of an insulation system but their behavior under electrical stress is not yet completely understood. In particular, when a dc voltage is applied, the electric field distribution at the interface is quite difficult to predict. This is mainly due to the accumulation of internal charge, which distorts the initial Laplacian field. To shed some new light on this topic, space charge measurements were performed on two types of coaxial XLPE-EPR interfaces. A numerical procedure, based on the Maxwell-Wagner theory for interfacial polarization, was developed for the estimation of the dynamic charge build-up at the interface. Experimentally obtained space charge profiles were compared to the calculated profiles. The limits of the Maxwell-Wagner model were assessed and the main parameters, which affect the interfacial polarization but which are not included in the model, were identified.