The acceleration effect of temperature change on water tree propagation

Abstract

To further understand the influence of temperature change on water tree propagation in XLPE (Cross-linked polyethylene) cables, the propagation characteristics of water trees in XLPE samples were investigated under temperature change (0°C transferred to 60°C, or 60°C transferred to 0°C). There were two kinds of samples: XLPE sheet samples, and cable samples. The XLPE samples were subjected to an accelerated water tree aging experiment under the condition of constant temperature and temperature change for water tree observation. While for the cable samples, they were subjected to voltage aging under the condition of constant temperature and temperature change for orientation analysis. The results of water tree observation showed that the growth rate of water trees aged under temperature change from 0°C to 60°C was significantly higher than that aged at the constant temperature of 0°C. The results of orientation analysis showed that the oriented XLPE materials in the cable samples can keep oriented for a certain period of time when the samples were transferred from 0°C to 60°C. According to the orientation theory in polymer physics, before disorientation, the severe molecular thermal motion at relatively high temperatures can act on the oriented XLPE materials and accelerate the fracture of the molecular chains, which further increased the propagation rate of water trees significantly.