【作者】 何鹏；

【导师】 肖文凯；

【作者基本信息】 武汉大学 ， 材料加工工程， 2022， 硕士

【摘要】 我国“西电东送”的特高压输电走廊在穿越西北大风区时,频繁发生导线断股事故,造成了重大经济损失。在大风作用下,导线主要做摆动运动,因此在线路架设时,广泛采用了金具串铰链连接导线末端,使导线摆动过渡到铰链中,以避免导线末端成为弯曲受力点而受损断股。但在线路实际运行中,却仍然发生了多次导线断股事故,并且近80%的事故都发生在引流线中。对比较为成熟的微风振动、次档距振荡以及覆冰舞动等断股机理,却发现引流线断股并不满足它们的前置条件。因而,大风区引流线断股可能对应着一种新的断股机理。因此,通过本文的研究既可以填补架空导线断股机理的研究空白,又可以为大风区引流线防断股治理措施提供新的理论支撑。本文首先统计梳理分析了大风区导线断股的积存案例,并重点研讨了引流线结构中的导线断股位置、外部环境特征以及引流线受风运动特点等系列相关因素。由于断股现场地理位置偏远,环境极为恶劣,无法在现场长期研究引流线的断股行为;同时,从现场获得的少量的断股导线断口也遭到了野外环境的侵蚀破坏,难以对其进行有效观察分析。为解决以上难点,我们在某750k V线路的48号塔引流线断股现场安装了导线工况监测系统,以获得现场风速、引流线摆动幅度、频率等数据,再以此搭建实验室引流线运动模拟试验平台。通过试验平台,模拟了引流线在5、6、7、8、9级风力以及5级7级交替风力中的运行工况。通过模拟试验,获得了大量断股导线试样,再利用SEM、TEM、3D轮廓扫描仪等观测分析断股导线的表面和断口等特征,结合材料失效分析相关理论,阐明大风区引流线的断股机理。对模拟试验结果的综合分析表明,导线在受风摆动过程中都会发生磨损现象,出现磨损斑特征,但很难诱导大风区引流线萌生微裂纹;所有试验导线断口中都具有明显疲劳失效特征;再进一步分析各组试验中的导线断股循环周次、断口疲劳条纹、导线内部晶粒变形的位错组态、表面宏观滑移线等特征,发现低于6级的风力对引流线损伤较小,损伤累积速率较慢,不会导致其频繁断股;但6级及以上的大风会使引流线发生应变疲劳(低周疲劳),导致其最外层导线表面在短时间内累积大量疲劳损伤而迅速萌生微裂纹,此后,各级风力都能促使微裂纹快速扩展,最终造成了导线发生频繁断股现象。基于此,本文提出了降低导线循环应力水平至屈服极限以下,避免应变疲劳,以延缓裂纹萌生的治理思路。鉴于大风区常伴随风沙的情况,本文还探索性地模拟了沙尘环境对导线断股的影响,结果表明沙粒冲蚀导线能够增加导线表面的疲劳强度,从而增加裂纹萌生所需的循环次数,有利于延长导线疲劳寿命。更多还原

【Abstract】 The conductors of UHV transmission line of"West-East Electricity Transmission Project"frequently break down when crossing through the strong-wind areas of Northwest China,resulting in significant economic losses.The conductors swing under the influence of strong wind.In order to avoid the end of the conductors becoming a bending force point and breaking down,hinges are widely used to connect the end of the conductor at the line erection stage.In this way,the swinging motion of the conductor can be transferred to the hinge.However,in the actual operation of the transmission line,there are still many broken strands accidents.In addition,nearly 80%of the accidents are caused by the broken strands of the jumper wires.Compared with the mature mechanisms of broken strands,such as aeolian vibration,sub span oscillation and ice galloping,it is found that the broken strands of jumper wires does not meet their preconditions.Thus,the broken strands of jumper wires in strong-wind areas may be caused by a new mechanism of broken strands.Therefore,the research of this paper can not only improve the research on the strand breaking mechanism of transmission line,but also provide new theoretical support for the measures to prevent strand breaking of drainage line in strong-wind area.This paper firstly analyzes the cases of broken strand of conductor in strong-wind areas statistically.Besides,it focuses on the relevant factors,including the broken strand position of the conductor in the drainage line,the external environment and the movement of the conductor.But due to the remote location and harsh environment of the strand breaking site,it is unable to continuously study the strand breaking behavior of the drainage line on the site.At the same time,the fractures of a small number of broken conductors obtaining from the site have been eroded and damaged by the field environment,so it is difficult to effectively observe and analyze.In order to solve the above difficulties,a conductor condition monitoring system was installed on the jumper wires of broke strands of tower 48 of a 750-k V Transmission line.The system can be used to collect data,including wind speed,swing amplitude and frequency of jumper wires,which can be used to build a laboratory jumper wire motion simulation test platform.The operating conditions of the jumper wires in the wind force of 5,6,7,8 and 9 and the alternating wind force of 5 and 7 are simulated on the simulation test platform.Based on the simulation test platform,we obtained a large number of broken strand conductors.Then use SEM,TEM,3Dprofile scanner and other instruments to observe and analyze the surface characteristics and fracture characteristics of broken strands of wire.At last,with the combination of the theory related to material failure analysis to elucidate the mechanism of strand breakage in the diversion line of strong-wind area.The comprehensive analysis of the simulation test results shows that the conductor will be worn and have the characteristics of wear spot in the process of wind swing.These characteristics can induce the initiation of microcracks in the sub outer conductor but it is difficult to induce micro-cracks in the windy areas of the diversion line.Fatigue failure characteristics were evident in all test conductor fractures.With further analyzing of the wire breakage cycle,fracture fatigue stripe,dislocation configuration of grain deformation in the conductors and surface macro slip line in each group of tests.It is found that the wind force below level 6 less damaging to the lead wire,and the accumulation rate of damage is slower and does not lead to its frequent breakage.However,the strong wind of level 6 and above can cause strain fatigue(low cycle fatigue)of the jumper wire,which result in the accumulation of a large number of fatigue damage on the outermost conductor surface in a short time and the rapid initiation of microcracks.Subsequently,wind forces at all levels can promote the rapid expansion of these microcracks,which eventually cause frequent strand breakage in the conductors.Based on the above mechanism,we put forward the treatment idea of reducing the cyclic stress level of the conductor below the yield limit and avoiding strain fatigue,so as to delay the crack initiation.Given that windy areas are often accompanied by sand,this paper also tentatively simulates the impact of sand and dust environment on broken strands of conductors.The results show that sand erosion of the conductor is conducive to increasing the fatigue strength of the conductor surface,thus increasing the number of cycles required for crack sprouting,which is conducive to extending the fatigue life of the conductor.更多还原