Space charge formation in XLPE-the influence of electrodes and pre-conditioning

The authors present space charge profiles for a range of XLPE planar samples under DC stress. Three different types of semiconductor electrodes were investigated, as well as vacuum evaporated Au. The samples were also subjected to three different heating/pumping pre-conditioning procedures. The space charge profiles in the unconditioned samples (heterocharge) were consistent with an apparent volume charge originating in a spatially inhomogeneous distribution of permanent dipoles. The profiles in the samples pre-conditioned at 80 °C and at atmospheric or rotary pump pressure (homocharge) suggested weak electron injection/extraction across the electrode/XLPE interfaces, followed by deep trapping close to the electrodes. Pre-conditioning at room temperature and rotary pump pressure produced space charge profiles very similar to those of unconditioned samples