特高压输电用换位导线铜的热效应

Cold-working strengthened copper material has been widely used as conductive components in the ultra-high voltage transmission (UHVT). However, little attention has been paid to the inevitable Joule heat induced softening of the copper, which may cause catastrophic accidents. Here, we quantitatively investigated the hardness change of copper specimens from continuously transposed cables of UHVT system under two typical working temperature ranges. We demonstrate that the micro-hardness decreases 2% ~ 5% under normal working temperature range for only 168 h (~ 0. 04% of the target lifetime). In addition, the hardness reduction can reach up to ~ 50% under the estimated short-circuit temperature range for only 1 h. Microstructural characterizations based on EBSD and TEM reveal that there is no obvious change in grain morphology and only slight decrease of dislocation density in specimens heated at normal working temperatures even for 168 h. Under short-circuit condition, heating at 400 ℃ for 1 h brings destruction of tangled dislocations but no grain growth, while substantial grain coarsening and dislocation annihilation are observed in samples heated at 600 ℃ for 1 h. Our work suggests that it's necessary and urgent to perform studies on mechanical properties evolution and lifetime evaluation of key component materials of UHVT under service conditions.