| Overhead transmission lines are the carriers of electrical energy transmission and are one of the most important infrastructures of modern society.Due to long-term exposure to the natural environment,the ambient temperature has a direct impact on the conductor load capacity and conductor temperature,and an indirect impact on the characteristics of parameters such as wire arc sag and stress.Especially in regions such as the northeast and northwest,where the temperature difference between the four seasons is large,the working environment of the conductor is particularly harsh.However,existing research is usually based on the assumption of room temperature or annual average temperature,and most of the research will be simplified to isothermal cylinders,lack of extreme low-temperature environmental conditions related to the study,ignoring the differences in the radial temperature distribution of the conductor,rarely consider the gap distribution,inter-strand contact and air convection conditions on the impact of radial temperature field.Therefore,the study of the dynamic characteristics of transmission conductors under extreme low temperature conditions is of great importance to ensure the structural safety of overhead transmission lines in cold regions and to carry out dynamic capacity increase of conductors to enhance the transmission potential of the lines.This paper firstly analyzes the self-damping characteristics of the wire under extreme low temperature conditions,followed by finite element modeling of the temperature field of the wire based on the principle of thermal equilibrium,studying the influence of different factors on the radial temperature field of the wire and summarizing the radial temperature distribution law of the wire,analyzing the stress distribution of each layer of the wire strands under different ambient temperatures and different radial temperature differences,and finally analyzing the temperature of the overhead transmission wire breeze The effect of vibration strength of overhead transmission lines is analyzed,and the effect of layered stress and temperature on the fatigue life of the wire is calculated.The main research contents and results of the paper include:(1)The effect of extreme low temperature conditions on the self-damping characteristics of the wire was studied.In the extreme low temperature conditions,theoretical analysis of the wire’s self-damping,the influence of low temperature on the wire’s self-damping characteristics.The test of two types of coductors self-damping under extreme low temperature is designed and conducted.The results show that:low temperature wire self-damping power is slightly lower than the self-damping power at room temperature,but the difference is not significant;frequency is certain,with the lowering of the ambient temperature,the wire amplitude is increasing,the wire self-damping power increases,therefore,low temperature conditions are more likely to occur in the wire breakage phenomenon,need to be taken into account in the design of the line in the extreme cold regions.(2)The effect of the extreme low temperature conditions on the radial temperature field distribution characteristics of the wire was studied.LGJ300/50 conductor as an example,the three-dimensional solid finite element modeling of the wire,calculated the radial temperature field of the wire,and analyzed the radial temperature distribution law of the wire under different working conditions.The results show that:in this paper the proposed method of numerical simulation of the radial temperature field of the wire has a high accuracy,numerical simulation method takes into account the existence of the air gap between the strands inside the wire more accurately reflect the actual situation of the internal structure of the wire,more accurate calculation of the temperature distribution inside the wire,to make up for the shortcomings of the IEEE calculation method;in the occurrence of convection natural convection and forced convection In the case of natural convection and forced convection,the radial temperature field of the wire presents the law of high surface temperature in the center,and the radial temperature distribution of the wire is not uniform,affected by the different contact conditions of each strand,the temperature of each strand has a large dispersion;for LGJ-300/50 type wire,the load capacity increases from 500A to 800A,due to wind speed,ambient temperature and other factors,the radial temperature difference of the wire can be 3～8℃;in low temperature environment,for the overall temperature of the wire,the change in ambient temperature has a greater impact,when the ambient temperature rises from-40℃ to 20℃,the overall temperature of the wire rose about 59℃,but the ambient temperature changes when the wire radial temperature difference is almost no change.(3)The effect of extreme low temperature conditions on the stress characteristics of the interlayer strands of the conductor was studied.Taking LGJ-300/50 conductor as an example,numerical simulations were conducted to analyze the effects of running tension and temperature load on the stress and strain distribution patterns of the strands in each layer of the conductor,and the results were compared with theoretical calculations.The results show that:when the ambient temperature is-40℃,the wire in the role of different operating tension,the stress value of the steel core part of the wire is higher than the outer aluminum strands,the overall stress state,the stress state of the same layer strands are similar distribution;due to the role of axial tension,the outer aluminum strand stress is greater than the inner aluminum strand stress,the outer strand axial strain is greater than the inner layer,in the long time load,plastic strain occurs first in the Under isothermal load conditions,as the wire temperature decreases.the stress in the internal steel core part of the wire gradually decreases.the stress in the external aluminum strand part gradually increases,due to the existence of the radial temperature difference of the wire,the outermost aluminum strand stress value of the wire increases with the increase in radial temperature difference,while the internal steel core and the inner aluminum strand stress shows a decreasing trend,when the radial temperature difference of the wire reaches 20℃,the outermost aluminum strand When the radial temperature difference of the wire reaches 20℃,the stress value of the outermost aluminum strand increases by about 27%compared with that without radial temperature difference,and the amount of stress change is directly related to the size of the radial temperature difference,and there is no direct relationship with the internal temperature of the wire.(4)The relationship between the fatigue life of the wire and extreme low temperature conditions is studied.Using the principle of energy balance method,the combined effect of temperature and wind speed of the wire breeze vibration characteristics of the analysis,taking into account the radial temperature difference of the wire and the influence of different strand layer stress distribution and other factors,the use of Miner damage accumulation theory,according to the wind speed and wind direction probability distribution,the fatigue life of the wire in extreme low temperature conditions is predicted.The results show that:without considering the effect of ambient temperature on the static stress,the fatigue life of the wire decreases with the decrease in ambient temperature,and the fatigue life of the wire changes significantly;the average stress of the wire strands has a greater effect on the fatigue life,and decreases sharply with the increase in the stress of the outermost layer;when the wire is energized and the static stress of the wire is considered,the fatigue life of the wire decreases with the decrease in ambient temperature.In this paper,the dynamic characteristics of the wire for extreme low temperature conditions carried out a systematic study,by considering the coupling of the ambient temperature and the structural properties of the wire.to obtain the extreme low temperature conditions of the wire from the damping change law,clarify the extreme low temperature conditions on the radial temperature field distribution of the wire,the strand layered stress characteristics and fatigue life of the impact of the law,the results of research to improve the load capacity of the wire,to explore the dynamic line has been built Capacity potential,enhance the level of wire safety design and fatigue life,to ensure the strength of the wire safety and arc sag safety distance provides a theoretical basis and basic data for the design and operation and maintenance of transmission line engineering in extreme environments to provide technical support,to ensure the safe and stable operation of transmission lines in cold regions laid a solid foundation. |
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