Effect of Cumyl Alcohol in Multilayer Dielectric on Space Charge Build Up

One of the issues of using cross-linked Polyethylene (XLPE) in DC insulation systems is the propensity of crosslinking byproducts to promote charge buildup inside the insulation, leading potentially to insulation failure. Field-induced ionization of the molecules, like in insulating liquids, is thought to be one of the processes of charge generation. In this paper, space charge measurement is realized to probe the effect of cumyl alcohol as one of the crosslinking byproducts. Low Density Polyethylene (LDPE) is used as polymer matrix, and soaked in cumyl alcohol. We show that polyethylene naphthalate (PEN) layers constitute efficient barriers to the evaporation of cumyl alcohol from LDPE films. The space charge behavior of soaked LDPE is compared to that of reference LDPE with PEN. Significant charge build-up occurs at the LDPE/PEN interfaces due to the conductivity gradient. PEN appears not suited for such analysis as the field is concentrated in the layer and is weak in the bulk LDPE.