Study On Wind Deflection Calculation Methods For Overhead Transmission Conductor Under The Acting Of Vertical Skewed Wind

Overhead transmission line is an important part of energy transmission,which plays an irreplaceable role in the development of social economy.At present,the domestic and foreign codes have made corresponding provisions for the wind load design of conductor,although the calculation methods are different,all codes are based on the characteristics of stationary winds.Different from the transmission tower,the transmission line has the characteristics of large span and small stiffness,and its dynamic behavior under wind load is very complex.The analysis of wind damage accident shows that the damage of transmission line is mainly caused by typhoon,hurricane,tornado and other extreme winds which exist vertical wind components.At the same time,China has a vast territory and complex terrain,transmission lines often need to cross hills,mountains and other microtopography conditions,and the characteristics of wind field under micro terrain are different from that of stationary wind.Therefore,it is necessary to analyze the response of the conductor under the acting of vertical skewed wind.In view of this,based on the cable theory,taking single span transmission line as the research object,this paper analyzes the disadvantages of the current codes,the static wind deflection,dynamic characteristics and gust response of conductor.The main research contents are as follows:（1）This paper compares the current load design codes of transmission lines used all over the world,and the difference of these codes be summarized.Compared with other codes,the load calculation value of Chinese codes is smaller,which is mainly due to the difference of wind-vibration coefficient,that may have adverse effects on the design of transmission lines.At the same time,the wind-induced vibration coefficient of Chinese code is less than 1 under specific conditions,which means that the total wind load is lower than the mean wind load;（2）Based on Irvine cable theory,the equilibrium equation of conductor under the combined action of horizontal wind and vertical wind has been established.The geometric nonlinearity under wind loads is considered in the equation.The static wind deflection displacement of transmission line under different conditions is calculated,and the influence of wind attack angle on the wind deflection of transmission line is discussed.The calculation formula of fundamental frequency proposed by Davenport and ASCE is modified,and the GRF is improved.Due to the difference of time interval between Davenport and ASCE methods,the ratio of resonance response and background response is quite different,and the calculation results of GRF are different obviously;（3）The characteristic equation of single span overhead conductor under static wind load is established,and the geometric nonlinear is considered.The calculation formulas of natural frequencies and mode shapes of in-plane and out of plane vibration of overhead conductor under combined wind are obtained.The validity of the derivation is verified by nonlinear numerical simulation,and the density of clustered modes is analyzed quantitatively.The results show that the modal frequency of the conductor changes greatly under the static wind load,and there are some differences in the fundamental frequency under different wind attack angles;（4）Considering the relative relationship between the conductor and wind,the dynamic equations of the conductor are established.Through the harmonic synthesis method,considering the spatial correlation and point correlation of wind velocity,the two-dimensional fluctuating wind speed at the node of the conductor is simulated,and then the wind load of each node of the conductor is obtained.Finally,taking a typical transmission line as the research object,the dynamic wind deflection of the conductor is calculated based on the nonlinear finite element method.The results show that the fluctuating part of vertical wind load has little effect on the response of transmission conductor,and mainly affects the vertical displacement of transmission conductor.