Water trees in EPR cable insulation

An earlier observation of carboxylate ions in vented water trees in service-aged XLPE (cross-linked polyethylene) cable insulation is extended to bow-tie trees in lab-aged XLPE, to bow-tie and vented trees in lab-aged EPR (ethylene-propylene rubber) and to the surface of LDPE (low-density polyethylene) film aged in an electrolytic cell. The initiation sites for bow-tie trees in EPR frequently contain transition metal oxides. Water trees in EPR and lab-aged insulations are shown to share many common features with the more widely studied examples in film-aged XLPE. Ionic materials (carboxylates and metal ions) are present at high concentrations in the trees. The commonality of the chemical state of water trees in filled EPR compared to unfilled XLPE implies a common mechanism.<>