Effects of space charge and dipoles on dielectric relaxation of polyethylene and its ageing in humid environment

The present paper reports results of high field polarization and dielectric relaxation behaviour of crosslinked polyethylene (XLPE) aged at constant alternating field stress in a humid environment at room temperature. It is suggested that it is established a competitive process as the ageing progresses, involving a dipolar component originating from an expected increase in the polar moieties and a space charge component arising from injection from the field. The space charge component is observed to get more dominant as the ageing progresses. The situation may be reflected as a Quasi DC (QDC) process in the low frequency range with the ageing time, in addition to dipolar relaxation peaks obeying the fractional power law observed in the medium frequency range and in the high frequency range.