Role of charge injection in AC aging of polyethylene in dry and humid environment

Thermal transient current (TTC) and thermally stimulated discharge current (TSDC) methods have been used to investigate the role of charge injection and trapping in cable-grade cross-linked (XLPE) and nonstabilized polyethylene (PE) samples aged in a dry and a humid environment. The TTC and TSDC data showed that in PE samples there is a nonuniform distribution of charge in the bulk. It is suggested that these charges are ions. PE samples aged at 65°C exhibited evidence of charge injection during DC poling at a higher temperature, due probably to higher oxidation levels or ion penetration during the aging. The observed responses differ from those in XLPE samples aged in dry oxygen, where TSDC peaks occurred at a lower temperature and were probably due to a presence of different types of localized states