| High-voltage transmission line system is an important part of electric power facilities,failure will seriously affect our daily life and work.High-voltage transmission line,as a special long-span flexible structure,will producegalloping under the action of ice and wind load,which seriously endangers the security and reliability of power systems.The frequency of the transmission line is the same as that of the system.Galloping of transmission line belongs to non-linear self-excited vibration,its frequencysare 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.To reveal the distribution of the modal and the corresponding frequency ofthe non-high-difference continuous transmission lines,which aregallopingand regarded asan integrated system made up with several sub-structuresconsists of insulator strings and single-span conductors.The motion equation of continuous spans transmission line is establishedunder the harmonic excitation in a single sub-structure,andit is solved by the force and displacement boundary conditions between the various substructuresto obtain a calculation method for dynamic stiffness of continuous spans transmission line which consider the effectof adjacent conductor and insulator string.Natural frequency of conductors can be obtained by the value of dynamic stiffness.A strain section consists 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 modal of transmission line.In this paper,based on the modal synthesis method,the continuous spans transmission lines 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.The numerical examples show that the finite element results are same as the method results for multi-spans natural frequencies and associated modes,and various resonance conditions can be predicted by the transcendental equation from which the natural frequencies of the symmetric in-plane modes.In addition,the method can be generalized to the natural frequencies and associated modes for non-high-differencearbitrary 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.Due to the existence of the chord componentof gravity,thearbitrary height difference continuous transmission linesmake tension maldistribution in the conduct.Based on direct method,the frequencies and associated modes of single span conduct with height difference angle are obtained in this paper.The influence of the chord componentof gravity on modal and frequency is confirmed by the finite element results,which lay the foundation of the calculation of the arbitrary height differencecontinuous spans transmission line’s modal and frequency. |
