Research On Wind Vibration Response And Longitudinal Unbalanced Tension Of Transmission Tower Line System In Mountainous Areas With Large Height Difference

Overhead transmission lines,as the main carrier of current electrical energy transmission,are an important lifeline engineering infrastructure for the country.The transmission tower system is a highly flexible structure that is very sensitive to wind.The frequency of the tower system is very rich and often matches the frequency range of the pulsating wind to a very high degree,resulting in frequent wind damage to the tower system under wind load.In particular,the establishment of transmission lines in mountainous areas,towers are located in the location of the terrain,geomorphological variability,there is often a large difference in height between the tower and tower phenomenon,resulting in wind loads in the tower line system in the linear tower wire longitudinal unbalanced tension,easy to trigger the tower longitudinal string down phenomenon.In order to grasp the dynamic characteristics,wind resistance and potential risk of collapse of the tower system of transmission lines in mountainous areas,this paper carries out a wind vibration response analysis of the transmission tower system in mountainous areas,the response law of the longitudinal unbalanced tension caused by the wind in transmission towers and the wind resistance assessment of transmission towers.Firstly,a refined finite element model with two towers and three line sections was established to analyze the dynamic characteristics of the transmission tower system with bare towers and the tower line system considering the coupling effect of the guide wires;the wind velocity time range samples of the wind field in the transmission tower line system were obtained by simulation,and the wind loads of the towers were applied to carry out the wind vibration response of the transmission towers at 0°,30°,45°,60°,90 The wind vibration response of transmission towers with wind angles of 0°,30°,45°,60°,90°,etc.was analysed,and the displacement response and root mean square(RMS)values of the wind speed applied at the top of the towers located at the valley and mountain top positions in the large height difference tower line system were obtained;the influence of wind speed and wind angle on the wind vibration response of large height difference transmission towers in mountainous areas was studied;on this basis,the response characteristics of the main material axial stresses of the two towers and the tower collapse were further compared and analysed.On the basis of this,the response characteristics of the main materials of the two towers and the location of the weakness of the tower collapse are further compared and analysed.Secondly,the mechanism of the generation of longitudinal unbalanced tension in linear towers of transmission lines with large height differences in mountainous areas and its influencing factors were studied,the relationship between the overhanging insulator string offset and longitudinal unbalanced tension in transmission towers with large height differences and unequal pitch was established,and the relationship between the longitudinal wind deflection angle and longitudinal unbalanced tension under the action of wind loads was mastered;A model of the tower line system with different number of gears,such as two,three and four gears,was established to investigate the effect of the number of gears on the longitudinal unbalance tension of linear towers and the response characteristics of the longitudinal unbalance tension of towers at different locations in mountainous areas;the height difference and horizontal distance of the two towers were further changed to carry out wind vibration response analysis of the tower line system with various height ratios under different wind speed inputs,and then the relationship between the height ratio of the tower line system and the longitudinal unbalance tension was derived,and suggestions were made to modify the design values of the existing code regarding the longitudinal unbalance tension.Finally,for transmission towers in typhoon-prone areas,on the basis of transmission line field tower dynamic characteristics testing,foundation settlement,pole and overall deformation and other health tests,an accurate finite element calculation model of the transmission tower assessment object is established,and the design basic wind speed(with a 30-year or 50-year recurrence period)and the beyond,extreme disaster wind speed that the transmission tower may withstand during its whole life cycle are used as the wind speed levels for assessment input.Using the equivalent static load,static elastoplastic and dynamic time analysis,the tower is subjected to a full range of wind resistance calculations and analyses,completing the evaluation of a series of evaluation indexes such as pole compression to yield ratio,overall deflection ratio,hazard point collapse ratio and wind vibration force amplification factor.The analysis of the wind resistance of towers under different wind speeds and wind angles will result in the most unfavourable wind angles and collapse hazard locations of towers,forming a multi-level,multi-dimensional and multi-parameter comprehensive wind resistance assessment method and assessment system for transmission line towers.