The role of chain orientation on the propagation of water trees at different temperatures

The propagation characteristics of water trees at different temperatures were investigated, and the effect of chain orientation on water tree morphologies was revealed. Accelerated water tree aging experiment was performed respectively at 0°C, 20°C, 40°C and 60°C for XLPE specimens. The morphologies of water trees were observed by an optical microscope, and the sizes of water trees were counted. The results indicate that 40°C is a transition temperature for the changes of water tree morphologies and sizes. Water tree branches are individual and distinctly follow the lines of electric field below 40°C, whereas the branches tend to be dense above 40°C. According to the results, the motion of molecular chains plays an important role in the propagation of water trees. The propagation of water trees below 40°C mainly depends on the behavior of chain orientation. However, above 40°C, because the chain orientation is suppressed by the thermal motion, water tree propagation is mainly determined by the behavior of chain thermal motion.