Analysis On Nonlinear Galloping With Multimodal Coupling Of Iced Conductors

Transmission conductor is an important part of the power system and plays a key role in the transmission of electric energy.However,the surface of transmission conductors is easily covered with ice under the low temperature,rainy and snowy weather.The conductor with asymmetrical ice-coated cross section will produce low-frequency galloping with large amplitude under wind load,leading to serious accidents such as wire breakage,interphase short circuit,tower tilt or collapse.Therefore,studying the galloping characteristics of iced conductor is very important for the safety and stability maintenance of the transmission system.At present,many studies have been proposed for the galloping analysis of iced conductors.Among them,the nonlinear three-dimensional continuum dynamic model was presented,and most of them focused on the single-order modal coupling analysis in each direction.However,as a three-dimensional continuum,transmission line will produce multi-mode galloping in the in-plane,out of plane,and torsion directions.Therefore,it is necessary to study the multi-mode coupling characteristics of ice-coated conductors.The multi-modal coupling in the in-plane,out of plane,and torsion directions is considered in the thesis for the first time.A nonlinear dynamic model of iced conductor with multi-mode coupling is established by using Galerkin method to discretize the continuum conductor model.The Runge-Kutta method is used to solve the problem.Considering the wind environment,the vibration characteristics of the nonlinear system and the suspension height difference of the conductor,the galloping of the iced conductor and modal vibration characteristics are systematically analyzed.The main research work is summarized as follows:In the first part of this thesis,the multi-mode discretization of 3D continuum iced conductor model is carried out by using the Galerkin method,and the multi-mode coupling nonlinear dynamic analysis system of iced conductor is established.The stability of multi-mode coupled nonlinear system of iced conductor is judged based on the Lyapunov stability theory.Modal vibration responses of iced conductor under different critical wind speeds are obtained by the Runge-Kutta method,and the modal vibration characteristics of conductor galloping are analyzed.In addition,as internal resonance is an important characteristic of nonlinear system,the variation of modal vibration characteristics under different internal resonance conditions is studied.In the second part,the fluctuating wind is introduced on the basis of the research work in the first part.Considering the randomness of the wind field,the high-efficiency fluctuating wind simulation method based on the traditional harmonic superposition method and Hermite interpolation improved Cholesky decomposition is adopted to simulate the random wind field of transmission line,and the influences of fluctuating winds on the galloping characteristics and modal vibration characteristics are analyzed The modal vibration responses,effective wind angle of attack and dynamic aerodynamic coefficient are obtained by numerical method.The randomness of iced conductor galloping in the random wind field and the randomness of modal vibration when iced conductor galloping are analyzed.In the third part,the conductor is simulated to be built in the slope terrain considering the height difference of transmission line in the actual erection.The multi-mode coupling nonlinear dynamic model of iced conductor based on the slope of mountain is established by using the cable continuum modeling method.Firstly,the aerodynamic coefficients of iced conductor cross-section under different mountain slopes are obtained by CFD(Computational Fluid Dynamics).Then the modal vibration characteristics of iced conductor under different mountain slopes are studied by numerical method,which are conducted in the stable wind field and stochastic wind field,respectively.In this thesis,by establishing a multimodal coupling nonlinear dynamic model of ice-coated conductor,the galloping of ice-coated transmission lines and the vibration characteristics of various modes are systematically analyzed.This research work provides a theoretical basis for the prevention and control of galloping of transmission conductors,which makes contribution to maintaining the safety and stability of the transmission system.