Comparison between deteriorated region, precursor of electrical tree, and water treed region

When polyethylene is subjected to a high field in the presence of water, a water tree is formed. Under dry conditions, a deteriorated region forms gradually before initiation of an electrical tree. Fourier transform IR analysis showed that there were common polar groups in the deteriorated region, and water treed region. Scanning electron microscopic observation showed that both regions contained a number of microvoids. The formation of the deteriorated region increased AC ramp and positive impulse tree initiation voltage but decreased the negative impulse tree initiation voltage. The dried water-treed region showed the same effect. The experimental results suggest some similarities in structure and properties between the deteriorated region and the water-treed region