POLARIZATION AND DIELECTRIC BEHAVIOR OF AC-AGED POLYETHYLENE

High field polarization and dielectric relaxation behavior have been u sed to study the aging mechanisms of crosslinked polyethylene (XLPE) a nd low density polyethylene (LDPE) aged at constant alternating electr ical field stress in a humid environment at room temperature, For this study, the dielectric spectroscopy data in the frequency range of 10( -5) to 10(6) Hz and their comparative analysis, have been used to prov ide electrical analog models of the aging. The dielectric data in the frequency range of 10(-5) to 5 X 10(-2) Hz were calculated from the de sorption current, whereas bridge measurements provide the data in the frequency range of 10 Hz to 10(6) Hz. In addition, thermal transient c nrrent and thermally stimulated discharge current measurements have be en carried out in order to determine the polarization and space charge accumulation in ac aged polyethylene. A correlation has been observed in the behavior of polarization and dielectric relaxation in the pres ent work. The dielectric behavior of the XLPE cable samples and of the LDPE nat samples show a presence of both the inter-cluster (low frequ ency) charge exchange and the intra-cluster (high frequency) charge mo tion, the former mechanism becoming more dominant as the aging progres ses. For the XLPE cable samples ac aged in a humid environment at room temperature, relaxation peaks obeying the fractional power law have b een observed in addition to a quasi-dc process.