Development of water tree resistant XLPE compounds

This paper is intended to present the philosophies of Neste Chemicals for improvement of the water treeing properties of crosslinked polyethylene compounds. The main part is devoted to insulating compounds, discussing cleanliness, polymer modification and water tree retardant (WTR) additives. A short discussion on the improvement of semiconductive materials with respect to water tree behaviour concludes the paper. The various mechanisms for water tree retardation are discussed within the framework of a theory that may be considered as a combination of two major hypotheses for water tree growth. Water trees are seen as consequences of two degradation processes working in parallel and mutually reinforcing each another: an oxidative degradation and an electro-mechanical deterioration of the polymer