The mechanisms of vented water tree growth

The water around a field enhancing defect in a tree retardant insulation was measured, and the factors which influence vented tree growth in conventional XLPE (cross-linked polyethylene) insulation were investigated. In both experiments the growth sites were examined by infrared spectroscopy less than ten minutes after the applied voltage was removed. The water tree retardant insulation was strongly absorbing in the region of the infrared spectrum where the carbonyl absorptions associated with oxidation occur. This complication did not apply to the conventional XLPE insulation. There is little evidence of water agglomeration in tree resistant insulation prior to vented tree growth from moderate field enhancements. Infrared spectra of freshly grown vented trees have not shown evidence of oxidation. It is noted that care is needed to distinguish chemical deterioration from species which have migrated into the insulation