Study On The Fatigue Life Of Overhead Transmission Line Considering The Effects Of Different Temperature Fields

When overhead transmission lines are in working condition,high-voltage current will flow inside them,generating a large amount of joule heat,which will increase the internal temperature of the lines,and the working environment of transmission lines is mostly located in the field,and the wind speed and ambient temperature in nature directly affect on the wire,it will also affect the temperature inside the wire.When the temperature of the wire changes,it will also have an impact on the stress distribution inside the wire.At the same time,when the transmission wire is in operation,it will be affected by the wind speed and direction of the outside world,which will produce breeze vibration.Long-term vibration will cause fatigue damage to the wire and affect the service life of the wire.However,most of the current studies on the fatigue life of the wire breeze vibration have not considered the influence of the internal temperature of the wire.Based on the above reasons,this article takes LGJ-400/50 steel core aluminum stranded wire as the research object to study the internal temperature distribution of the wire under different wind speed,ambient temperature and current carrying capacity,and based on these,the internal stress distribution of the wire considering temperature effect is analyzed.Finally,based on Miner fatigue criterion,the breeze vibration fatigue life of the wire under different temperature and radial temperature difference is studied.The specific research work of this paper is as follows:(1)According to the thermal balance theory of the wire,the heat production rate of the steel core and aluminum strand wire under the different current carrying capacity of the wire is calculated.On this basis,the conjugate heat transfer of the finite element model of LGJ-400/50 steel core and aluminum strand wire was analyzed by CFD software Fluent.The analysis results show that the internal temperature of the wire decreases with the increase of wind speed,increases with the increase of the current carrying capacity,and increases linearly with the increase of the ambient temperature.At the same time,there is also a radial temperature difference between the strands inside the wire.(2)Based on the numerical simulation results of the internal temperature field of the wire obtained in the Fluent numerical analysis,the internal temperature stress of the wire is analyzed separately without considering the operating tension and the operating tension.The research shows that: When the operating tension is not considered: Every 50 A increase in ampacity,the average stress of the steel core layer,the first and second layers and the third layer of aluminum strands will increase by about 5MPa,3.5MPa,3MPa and 2MPa respectively;the increase of wind speed will reduce the average stress of the wire;with the change of the ambient temperature,the position of the maximum stress inside the wire has been changed.When considering operating tension: for every 10°C increase in ambient temperature,the average stress of the steel core layer will increase by about 9 MPa,and the average stress of the aluminum strands of the first,second and third layers will decrease by about 2.5 MPa,1.5 MPa,1.5 MPa and 1MPa,respectively;for every 5℃ increase in the radial temperature difference inside the wire,the average stress of the steel core layer is reduced by about 3MPa,the average stress of the first layer of aluminum strands is reduced by about 0.6MPa,and the average stress of the second layer and the third layer of aluminum strands increase by about 1MPa.(3)According to the simulation results of the temperature stress of the wire under consideration of operating tension,based on the principle of energy balance,combined with the distribution probability of wind speed and direction,and based on the Miner fatigue cumulative damage criterion,the fatigue life of the wire under the influence of temperature is predicted.The research conclusion is: The fatigue life of the wire increases with the increase of the ambient temperature,and decreases with the increase of the radial temperature difference.