From LDPE to XLPE: Investigating the change of electrical properties. Part I: Space charge, conduction and lifetime

This paper discusses the results of space charge, conduction current and electrical lifetime measurements performed on widely-used materials for electrical insulation, that is, low density polyethylene (LDPE) and cross-linked polyethylene (XLPE). Space charge accumulation profiles were compared in LDPE, low density polyethylene plus antioxidant (LDPE + AO) and XLPE, with consideration of thermal treatment effects in LDPE and XLPE. Significant variation (decrease) of accumulated space charge and apparent mobility, as well as slight decrease of conduction current, can be seen going from LDPE to LDPE + AO and XLPE, which may be associated with formation of deeper trap levels (or an increase of their density). On the contrary, electrical life under ac voltage does not show significant differences from LDPE to XLPE. This latter result underlines that life under high ac electrical stress is mostly determined by defects (weak points) rather than material characteristics associated with charge injection and transport.