Charging and polarization phenomena in XLPE-EPR coaxial interfaces

Interfacial charge build-up has been investigated in crosslinked polyethylene (XLPE) and ethylene propylene rubber (EPR) coaxial interfaces. For this purpose, space charge measurements have been performed on cables where the insulating part is composed of two dielectric layers consisting of EPR and XLPE. Measurements were carried out at different temperature gradients across the insulation by means of the pulsed electroacoustic method (PEA). Significant charge build-up was measured at the EPR/XLPE interface when a DC voltage was applied on the cable conductor. Interfacial charge magnitude and time required for the charge to accumulate were found to be strongly dependent on the interfacial temperature. On the other hand, the temperature gradient experienced by the cable insulation was found affecting the space charge in the bulk of the EPR. From the experimental space charge profiles, the electric field distributions within the two dielectric layers of the cable were deduced. A characteristic similarity of all the measurements was that the electric field within the XLPE was enhanced by the presence of interfacial charge.