Aeolian Vibration Mechanism Of Long-span Overhead Conductor Consider Vertical Wind Shear

The safe operation of transmission lines is an important link to ensure the national power supply.Due to the special structure of long-span transmission line,it is easy to induce the sustained aeolian vibration of the conductor under the low-speed laminar wind,which causes the fatigue break of the conductor and the damage and failure of the anti-vibration metal fittings.It is of great theoretical and practical value to understand the mechanism of aeolian vibration of long-span conductor.This paper comprehensively evaluates the operating environment and structural characteristics of long-span conductor,and focuses on the large sag characteristics of long-span conductor,considering the actual law of wind speed distribution with vertical shear in flat terrain,the local lock-in mechanism of aeolian vibration of long-span conductor is proposed.The main research and results of the paper are as follows:1)Local lock-in theory and model of aeolian vibration of long-span conductor.Based on large sag of long-span conductor and the distribution of wind speed with height gradient,it is proposed that in the vertical shear wind field,wind load and long-span conductor are more likely to form ’local lock-in’ phenomenon.Local locking is simplified to local excitation,a damped one-dimensional continuous string model is established to study the lateral aeolian vibration behavior of conductor.2)Study on propagation and dispersion of aeolian vibration wave of conductor.From the perspective of wave propagation,the dispersion relationship between complex wave number,phase velocity and frequency of four degradation models,and the influence of elastic stiffness and damping on vibration wave propagation are analyzed.It is pointed out that when the excitation frequency is greater than the critical frequency,the vibration wave of the conductor model is the propagation traveling wave in two opposite directions.In the propagation process,the phase velocity of each order frequency is mainly determined by the structural parameters,and the elastic stiffness makes the vibration wave dispersive.Damping determines the attenuation characteristics of vibration waves in the propagation process.3)Green’s function solution of aeolian vibration of long span conductor under local excitation.The local excitation is further simplified as the point source excitation,and the aeolian vibration model of the infinitely long damped conductor under the local point excitation is constructed.The explicit Green’s function solution of the model response is derived in detail by using the integral transform method and the residue theorem,and the validity of the small damping solution is verified.The influence of structural parameters and excitation parameters on the wave response is studied.It is pointed out that the response of long-span conductor model under harmonic point source excitation is a traveling wave with spatial attenuation from the excitation source along the conductor to the two sides of the support end,and its traveling wave characteristics are related to the excitation frequency ratio and the damping ratio of the system.the self-developed image measurement technology is used to carry out the local excitation experiment of the conductor,the propagation evolution of the traveling wave in the conductor are qualitatively verified.4)Study on the characteristics of aeolian vibration wave of long-span conductor under local excitation.The aeolian vibration model of the damped conductor with support end constraint under point source excitation at any position is constructed.Based on the small damping characteristics of the long-span conductor,the explicit expression of the fluctuation response of the long-span conductor under periodic point source excitation is obtained.It is pointed out that the vibration wave of the damped conductor is the superposition of the standing wave and the traveling wave.The discriminant parameters of the wave type of the conductor are determined in the form of the product of the vibration modulus and the damping ratio,and the qualitative relationship between the discriminant parameters and the wave type is given.It is pointed out that the amplitude of the vibration wave is the largest when the excitation position acts on the ideal peak of the vibration wave.The experiment of vibration under local wind excitation is carried out,and the signal of vibration is obtained by video acquisition and image processing.The experimental results are in agreement with the theoretical analysis,including the stable standing wave vibration of the conductor caused by local excitation and the absence of ideal wave nodes.5)Research on modal damping ratio of conductor with additional local external damping.combined with the structural characteristics and working principle of the commonly used vibration prevention measures of long-span conductor in engineering,the typical damper is simplified as a spring mass oscillator system.The conductor system model with additional local external damping is constructed,and the complex characteristic frequency of the system is calculated.The influencing factors of the modal damping ratio of the system are analyzed,and the influence laws of the equivalent parameters and installation parameters of the local external damping on the damping ratio of the system are pointed out.The above research reveals the evolution law of aeolian vibration wave of long-span conductor after local lock-in,puts forward the distinguishing parameters and conditions of aeolian vibration wave type of long-span conductor,theoretically gives the influencing factors of modal damping ratio of conductor system.