Dielectric spectroscopy of polyethylene in the frequency range of 10(-5) Hz to 10(6) Hz

Polyethylene, one of the most widely used electrical insulating materials, is known, despite its excellent physical properties, to exhibit structural degradation when submitted to a continued electrical (AC) stress in a humid environment. Although much work has been done to correlate the inception and growth of water trees with the breakdown in polyethylene, little attention appears to have been given to identify, through an appropriate model, the deterioration of the electrical and dielectrical parameters with the progressive aging of the insulator. This paper reports the results of a comprehensive study of electrical aging of both low-density polyethylene (LDPE) and chemically crosslinked polyethylene (XLPE) aged in humid environment at an AC stress of 6 kV/mm for an extended time. For this study, dielectric spectroscopy in the frequency range of 10(-5) Hz to 10(6) Hz has been employed to provide appropriate electrical analog models of the aging. An agreement, at least qualitative, is found with the dielectric and the thermally stimulated discharge current (TSDC) behavior.