Study On Aeolian Vibration Of Transmission Line And Its Prevention

Aeolian vibration of overhead transmission lines is vortex-induced vibration caused by Karman vortex streets and the coupling vibration of conductor motion and vortex excitation.The amplitudes of aeolian vibration are small,but its vibration frequencies are high,the duration is long,and some lines even are under aeolian vibration all year long.Aeolian vibration can cause lots of accidents,such as: the conductor breakage and the slack of the clamp at the joints of the suspension clamp,vibration damper and spacer.The accidents of conductor breakage caused by aeolian vibration still takes place occasionally even though there are a lot of research results on aeolian vibration of conductors.Therefore,it is of great significance to study the characteristics of aeolian vibration of transmission lines and consider its suppression method to reduce the line accidents of conductor breakage and ensure the safe and stable operation of power system.Firstly,a wake oscillator model is used to describe the fluctuating nature of vortex shedding on the leeward side of a conductor,and a nonlinear numerical simulation method of aeolian vibration of a single conductor line under the coupling effect of conductor motion and vortex excitation is studied.Compared with the energy balance method and the dynamic method without considering the coupling effect of conductor motion and vortex excitation,the vibration characteristics can be revealed more truly and the understanding of vibration mechanism of aeolian vibration is also deepend.Using this method,the lock-in phenomenon of aeolian vibration is revealed by this three-dimensional(3D)numerical simulation for the first time.It is found that the phase difference between the lift and the displacement of conductor is about 90° in lock-in domains,and the vibration finally stabilizes to single frequency.In the range out of the lock-in domains,the phase difference is unstable and the vibration appears "beat phenomenon".The nonlinear numerical method of aeolian vibration of conductors considering the coupling effect of conductor motion and vortex excitation has laid a foundation for the further study of aeolian vibration characteristics.The mechanical properties of steel and aluminum wires in conductor are obtained by uniaxial tensile tests.Considering the structural details and the complex friction,extrusion and slippage among wires of the conductors,3D refined FE models of the typical aluminium conductor steel reinforced(ACSR)and formed aluminium conductor steel reinforced(FACSR)are set up.Furthermore,the elastoplastic deformation and stress of the two types of conductors as well as the tension-torsion coupling effect under static tensile and dynamic load are analysed.It is found that it is necessary to take into account the effect of the structural details of conductors on their mechanical behaviour in the design of transmission lines.The maximum Mises stresses in the layers of conductors are ranked in descending order as outer steel,steel core,inner aluminum and outer aluminum in static axial loading and dynamic ice-shedding situations.Under the same tensile load,the maximum stress in the wires of ACSR is much larger than that of the wires of FACSR,which indicates the safety of the latter one is higher than that of the former under the same load.The obtained results provide a reference for the study of damage degree and failure mechanism of conductor under loading.The 3D refined FE model of the conductor and the complete suspension clamp is established taking into account the friction,extrusion,slippage between the suspension clamp and the conductor and between the wires inside the conductor as well as the initial bending of the conductor.This model is more reasonable compared with the half model of suspension clamp and conductor in the literatures.The elastoplastic dynamic responses of the conductor under aeolian vibration are investigated,and the stress,deformation,fretting wear and fretting fatigue of the conductor are analyzed.It is found that the actual bending stiffness of the conductor should be considered if the amplitude of the conductor near the clamp is studied.The initial bending of the conductor has an obvious effect on the stress state of the conductor near the suspension clamp.As the amplitude increases,the maximum stress of the aluminum wires shifts from the outer layer to the inner layer.With the decreases of the friction coefficient,the maximum Mises stress of the inner aluminum wire increases,but the Mises stress of the outer aluminum wire decreases.As the friction coefficient increases,the conductor is more prone to fatigue when the amplitude of the conductor is kept constant.With the increase of amplitude,the influence of friction coefficient on the maximum slip displacement decreases.The influence of friction coefficient on slip displacement and wear of the outer layer is more obvious than that of the inner layer.The inner layer of the conductor is more prone to wear than the outer layer.The analysis results provide a reference for the study of fretting fatigue and fretting wear mechanism of aeolian vibration of conductors.New types of vibration damper for aeolian vibration are proposed and its design method is given in order to solve the problem that the dangerous frequencies of the aeolian vibration of the conductor do not match with the natural frequencies of the vibration damper and the steel strand of the Stockbridge damper is easy to be damaged.The masses,dampings and natural frequencies of the vibration damper can be designed according to the protection frequencies of a specific line.The suppress effect of the new types of vibration dampers on the aeolian vibration of the conductor is studied by the numerical simulation and compared with that of the Stockbridge damper.It is found that the suppress effect of the new type of vibration damper is better than that of the Stockbridge damper when the masses,damping ratios and natural frequencies are equal.By designing the masses,damping ratios and natural frequencies of the new types of vibration dampers for a specific line,better damping effect can be obtained.For twin bundle conductor in tandem arrangement,taking into account the coupling effect of conductor motion and vortex excitation and the influence of wake flow,and using two wake oscillator models to describe the fluctuating nature of vortex shedding behind the two conductors,as well as the coupling term of the oscillator to describe the aerodynamic coupling effect of the upstream sub-conductor on the downstream sub-conductor,the nonlinear numerical simulation method for aeolian vibration of twin bundle conductor line is studied.And the method is used to simulate the aeolian vibration characteristics of twin bundle conductor.It is found that due to the influence of spacers the amplitudes in sub-spans of the twin bundle conductor line are not equal when the vibration frequency is greater than 10 Hz.In lock-in domains,there is a transition in the vibration pattern,where the amplitudes and frequencies change abruptly.When there is no spacer in a line,the vibrations of the two sub-conductors are in the same frequency but there are phase differences between them due to the influence of the wake.After the spacers are installed,the amplitudes of the two sub-conductors are almost equal,and the motion is in phase or out of phase.At some frequencies,the spacers change the vibrational waveform of the line.Research results in this paper provide a reference for the study of characteristics,failure mechanism and suppression method of aeolian vibration of transmission conductors,which has important theoretical significance and engineering application value.