Effects of crosslinking byproducts on space charge formation in crosslinked polyethylene

Space charge is formed in cables insulated with crosslinked polyethylene. It has not been clear whether the crosslinking byproducts or the crosslinked polymer morphology is responsible for the space charge formation. In order to clarify this point additive-free noncrosslinked low-density polyethylene, additive-free crosslinked polyethylene, and degassed crosslinked polyethylene were soaked in the crosslinking byproducts and the space charge distribution was measured after DC voltage application. Samples tested are divided into two categories. The first category is a soaked single-layered sheet and the second category is a two-layered specimen consisting of a soaked sheet and a nonsoaked sheet. As a result, the following conclusions were obtained. (1) Cumyl alcohol is responsible for homocharge layers in front of the electrodes in both low-density and crosslinked polyethylene sheets. (2) Acetophenone is responsible for heterocharge formation in crosslinked polyethylene, presumably as a synergistic effect with water. (3) alpha -methylstyrene has no effect on space charge formation in low-density polyethylene, while it assists charge trapping in crosslinked polyethylene. (4) Charge trapping occurs easier in degassed crosslinked polyethylene than in low-density polyethylene, probably because of carbonyl groups induced by crosslinking