Comparison between water-treed and deteriorated regions. Electrical tree precursor

When polyethylene is subjected to high fields in the presence of water, a water tree may be formed. However, under dry conditions a `deteriorated region´ is gradually formed before the initiation of an electrical tree. The experimental results suggest some similarities in structure and properties between the deteriorated and the water-treed regions. FTIR analysis shows that there are common polar groups in these regions. Scanning electron microscope observation found a number of microvoids in both regions. The formation of the deteriorated region increases the resistance to electrical tree initiation during subsequent ac ramp voltage and positive impulse voltage but decreases it for negative impulse voltage. Dried water-treed regions show the same effect