Accelerated aging of crosslinked polyethylene cable insulation; positron annihilation spectroscopy study

The authors describe results obtained by using the technique of positron annihilation spectroscopy to examine the free volume of cross-linked polyethylene (XLPE) insulation from 15-kV cables that had been subjected to laboratory accelerated aging. Conclusions on free volume presence and content are drawn from o-positronium lifetime and intensity. The limited number of experiments suggest that the free volume content was greatest in unaged cable, drops upon initiation of aging, and then increases upon continued aging. For the accelerated aging conditions used, the free volume did not reach the initial level even after 900+ days of aging. Observed changes were small, and DC voltage did not appear to have an effect on total free volume. These results may be related to the specific cable aging conditions used. Conventional microscopy results on similar cables are also provided.