Polarization phenomena in cross-linked polyethylene (XLPE) containing water-trees

The authors report preliminary results of a polarization study using thermally stimulated discharge current (TSDC) measurements and the thermal current transient technique on XLPE (cross-linked polyethylene) samples in which water trees have been grown. A schematic representation of the observed current transients at the onset or removal of a step input of thermal radiation is shown. Values of the peak thermal transient current I_p of control samples and aged samples after poling at 6.14×10⁶ Vm^-1 and after the TSDC runs are given. It may be observed that the I _p value increases by two orders of magnitude after aging of 472.2 h followed by a DC poling at a field of 6.14×10⁶ Vm^-1. In addition, the TSDC spectra for (unaged) control samples and samples in which water trees have been grown are shown. It is observed that the dominant TSDC peak at 80°C increases significantly for samples with increasing aging time