某500 kV输电导线在架线施工过程中发生断裂，通过宏观观察、几何尺寸检测、化学成分分析、力学性能试验、断口形貌宏微观分析、模拟试验等方法对导线的断裂原因进行了分析。结果表明：导线结构尺寸、力学性能及材料正常；断口均为典型的正向拉断断口，未发现原有缺陷；通过设计导线的逐层拉断试验及现场力学条件的模拟试验，发现导线在加载至紧线器额定载荷时并未发生滑移及断裂，在接近导线额定拉断力时整体断裂，对比试样与现场断裂导线的断口形貌，确定导线是在施工过程中严重过载，于紧线器夹持位置发生逐层断裂。

A 500 kV transmission wire fractured during the construction process. The reasons of the fracture were analyzed by macroscopic observation, geometric size detection, chemical composition analysis, mechanical property test, fracture surface macro and micro analysis, simulation test and so on. The results show that the structure size, mechanical property and material of the wire were normal, the fracture was the typical forward tensile fracture, and no defects were found. Through the design of the wire layer-by-layer tensile test and the simulation test of the field mechanical condition, it was found that the wire did not slip and fracture when the tightener was loaded to the rated load, and the whole fracture happened when the load was close to the rated pulling force of the wire. In comparison with the fracture morphology of the specimen and the fractured wire, it was determined that the wire was overloaded in the construction process, layer-by-layer fracture occured at the clamping position of the tightener.