Dynamic Characteristic Analysis Of Continuous Transmission Line

High-voltage transmission line system is an important part of electric power facilities,if the system was damaged,heavy losses of our daily life and production will be caused.High-voltage transmission line,as a long-span flexible structure,will produce galloping under the action of ice and wind load.It severely threatens the security and reliability of power systems.Galloping of transmission line belongs to non-linear self-excited vibration,its frequency are same as a certain natural frequency of system.So the change rules of modal and natural frequency of transmission line are theoretical foundation for researching transmission line galloping,it is of great project practical value.Numerical results show that in galloping of iced conductor,adjacent gear conductor has obvious effects amplitude of galloping of galloping conductor,and high voltage transmission lines are generally continuous transmission line,when the galloping occurs,the conductor adjacent to the galloping conductor is generally in a state of motion,if the equivalent static stiffness is used to simulate the influence of the conductor on the galloping,it ignores the adjacent conductor movement effect.In order to reveal the interaction between each span of conductor galloping,the motion differential equation of continuous spans conductor under the harmonic excitation is established by taking insulator string and single-span conductor as substructure.Continuous conditions for force and displacement of the substructure are utilized to solve the above equation,and then a calculation method for dynamic stiffness of continuous spans transmission line which consider the effect of adjacent conductor and insulator string is presented.Dynamic stiffness get by the method can more accurately reflect the dynamic effects of adjacent multiple conductor and insulator string on galloping span transmission line.The accuracy of calculation method for the dynamic stiffness of continuous spans transmission line is proved with the help of finite element method.The result showed that harmonic excitation frequency equals the natural frequency of continuous spans conductor when the dynamic stiffness reaches its maximum value.Based on this conclusion,the natural frequency of continuous spans conductor can be obtained.Moreover,the possibility of simplifying continuous spans conductor as spring-particle is discussed on this basis.A specific example given has shown the dynamic stiffness curve of continuous spans conductor and simplified model are uniform by adjusting the spring stiffness ratio and damping under the premise of the same static stiffness and frequency between them.The simplified model can more accurately reflect the dynamic relationship between galloping span conductor and adjacent span conductor,and make the researches on the mechanism of transmission line galloping become more convenient.A strain section consist of multi-span transmission line,different lines influence each other as a unit due to suspension insulator string may vibrates along the string-direction.The research on modal and frequency of a strain section can reflect the galloping mode of transmission line.In this paper,based on the modal synthesis method,the continuous spans transmission line are simplified to multiple single line.Then,based on the dynamic stiffness method,the in-plan natural frequencies and associated modes for two-span conductor and three-span conductor were presented by application of displacement continuous conditions and moment equilibrium equation.Numerical examples showed that the finite element results were in agreement with new method results for multi-spans natural frequencies and associated modes,but the new method was a quick and convenient way to obtain natural frequencies of multi-spans conductor.Various resonance conditions can be predicted by the transcendental equation from which the natural frequencies of the symmetric in-plane modes.In addition,the new method can be generalized to the natural frequencies and associated modes for arbitrary multi-spans conductor.The natural frequencies and associated modes are applied to theoretical analysis on aerodynamic stability and dynamic response of continuous spans transmission line.