Roles of cumyl alcohol and crosslinked structure in homo-charge trapping 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 low-density polyethylene, crosslinked polyethylene, and degassed crosslinked polyethylene were soaked in cumyl alcohol and the space charge distribution was measured under dc voltage application. Specimens 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 non-soaked sheet. As a result, the following conclusions were obtained. (1) The crosslinked structure has no effect on homo-charge layers. (2) Cumyl alcohol is responsible for traps in both cases of low-density and crosslinked polyethylene. Due to these traps, a homo-charge layer appears in front of each electrode in the single-layered sheet or on the surface of the soaked sheet facing the opposite electrode in the two-layered sample. (3) More space charge is trapped in crosslinked polyethylene than low-density polyethylene, probably because of the presence of carbonyl groups.