The Role of Electrical Orientation on Water-Tree Propagation at Different Temperatures

摘要

To understand propagation characteristics of water trees at different temperatures, the effect of molecular chain orientation on morphologies and sizes of water trees was investigated. An accelerated water tree aging experiment was performed at 0°C, 20°C, 40°C, and 60°C for XLPE specimens respectively. The morphologies and the sizes of water trees were observed via an optical microscope. The results indicate that 40°C can be a transition temperature for the changes of water tree morphologies and sizes. At 0°C, the water tree sizes reach the maximum value among the four temperatures. From 0°C to 40°C, the water tree sizes decreases and reach the minimum value at 40°C. From 40°C–60°C, the water tree sizes increase again. Moreover, the dendritic water tree branches can be observed, and the separate water tree shape become blurry with the increase in temperature. While above 40°C, there are sheet water trees from which separate water tree branches cannot be distinguished. Based on the orientation theory in high polymer physics, the orientation of XLPE molecular chains can play an vital role in the propagation of water trees. Above ?5°C, the motion of the molecular chain segments of XLPE is activated and the XLPE can be oriented under the effect of the electric field. In low-temperature region, the XLPE can be oriented under the effect of the electric field, which can promote water-tree propagation. However, with the increase temperature, the molecular thermal motion become severe, and the orientation degree of the XLPE can decrease. Accordingly, the propagation rate of water trees decreases.