Temperature characteristics of water tree propagation in a wide temperature range using XLPE sheets

Water tree propagation depends on temperature. However, water tree propagation in a wide temperature range remains to be elucidated. In this study, we investigated the temperature characteristics of water tree propagation from -20°C to 80°C in cross-linked polyethylene (XLPE) sheets. The water tree observed has a radial structure with a fanlike or human-hand-like shape at low temperatures (-20°C~room temperature), but a dense-ball-like or sphere shape at high temperatures (50°C~80°C). On the basis of the results of our microscopy observation of a water tree, we considered water tree propagation in two temperature ranges: low temperatures and high temperatures. Furthermore, for the growth mechanism of water trees, we suggested that an electromechanical factor is dominant at low temperatures, whereas an electrochemical factor in addition to an electromechanical factor is dominant at high temperatures.