On the nature of AC field aging of cross-linked polyethylene using liquid electrodes

The nature of AC field (6 kV mm-1 and 1 kHz) aging of cross-linked polyethylene (XLPE) with (i) NaCl and (ii) CuSO4 (0.1 M) liquid electrodes has been studied with thermally stimulated discharge current (TSDC), thermal transient current (TTC) and Fourier transform infrared spectroscopic (FTIR) techniques. The behaviour of thermal transient current appears to be related to the electrical aging time and consists primarily of two components, i.e. dipolar and space-charge contributions. The magnitude of the TTC is related to that of the integrated charge released in a TSDC thermogram. FTIR measurements show that oxidation of stabilized XLPE is significantly lower than that of the unstabilized polymer. No noticeable increase in bound water content in the polymer was observed as measured by IR absorbance at approximately 3370 cm-1. Progressive enhancement of absorbance at approximately 1715 cm-1 and the TSDC peak at 70 degrees C with increasing field aging time appear to have the same origin.