强风区750 kV超高压输电线路引流线断股机理研究

Study on lead wire breakage mechanism of a 750 kV UHV transmission line in strong wind zone

强风区750 kV超高压输电线路某铁塔引流线发生频繁断股事故,造成了重大经济损失。结合风区气象条件对该线路铁塔输电结构进行了细致分析,发现与边相引流线不同的是,该铁塔的中相引流线因塔型结构所限,在安装时需在空间上有一弯曲折线段,该弯曲段极易受大风载荷作用而往复摆动。通过实地安装导线摆动监测系统,得到导线摆动角度和风速的对应关系,将之应用在自行搭建的导线摆动疲劳试验平台中,进行8级风下的导线摆动试验。试验发现,导线最早在17万次摆动后发生断股,断股导线表面出现宏观滑移带,利用3D轮廓仪测得滑移带形貌。对比试验导线和新导线的电阻率、纳米压痕硬度和拉伸强度,发现试验导线的电阻率上升,显微硬度增加,屈服强度提高,显示出明显的屈服变形特征。TEM观察显示,试验导线出现了位错增殖和晶粒变形;SEM断口分析表明,试验导线断口具有明显的低周疲劳断裂特征。

Frequent breakage accidents occur on the lead wires of a 750 kV ultra high voltage(UHV)transmission tower in strong wind zone,which has caused serious economic losses.In this paper,the transmission structure of the tower is analyzed in detail based on the meteorological conditions of the wind zone.It is found that there is a curved fold part of the lead wires of tower in middle phase during installation because of the limitation of tower structure.This curved part can easily reciprocate due to large wind loads,which is different from the lead wires at the side phase.A wire swing monitoring system is installed on site to obtain the corresponding relationship between the wire swing angle and the wind speed.These data are used in the selfbuilt wire swing fatigue test platform to carry out a wire swing experiment under the condition of wind speed reaching grade 8.It is found that the first strand breakage occurs after 170000 oscillations of the wire.A macroscopic slip band appears on the surface of the broken strand,and the morphology of slip bands is measured by a 3 D profilometer.The electrical resistivity,nano indentation hardness and tensile strength of the experimental wires and the new wires are compared,and it is found that the electrical resistivity of the experimental wire,the nano indentation hardness,and the tensile strength have increased,and the yield deformation characteristics are obvious.TEM observations show that dislocation multiplication and grain deformation have occurred in the experimental wires.SEM fracture analysis shows that the experimental wires have obvious characteristics of low cycle fatigue fracture.