| China’s high-voltage transmission lines have entered a period of rapid development,and the demand for ultra-high-voltage transmission lines is increasing.The safe operation of transmission lines has become a key research object at home and abroad.Because of its wide range of distribution,passing through mountains and rivers,and long-term external factors,including wind,rain,lightning,ice and so on,it is easy to cause overhead transmission lines can not operate normally.High voltage transmission lines are mainly continuous conductors,which have the characteristics of large span and strong flexibility.They can only bear tension,but can not be compressed.In extreme bad weather,serious icing of transmission lines and galloping of non-circular cross-section conductors may occur when the wind passes through the iced conductors.With the continuous growth of galloping time,malignant accidents such as broken strands and broken wires of overhead wires,shifting of fittings,disconnection of insulator strings and overturning of poles and towers will occur,which will bring different degrees of harm to the transmission line system and affect the normal operation of the power grid system.In order to reveal the influence of terrain change on the dynamic characteristics of continuous transmission lines,a dynamic stiffness theory based on arbitrary elevation-difference angle is proposed.First,single-span conductors are regarded as independent substructures of continuous transmission lines,and the vibration equation of single-span conductors with two suspension points at different elevation-difference angles is constructed.A quadratic term is introduced into the theoretical equation,which can take into account the shadows of gravity chord component.The calculation method of dynamic stiffness of insulator string rotating around its suspension point is deduced.The transverse vibration modes and frequencies of continuous conductor are studied by dynamic stiffness theory.The accuracy of theoretical modal and frequency formulas is verified by finite element software ABAQUS.The results show that the method of calculating dynamic stiffness has high accuracy,and the theoretical modal accords with the finite element results.The frequency and modal obtained at the same time can provide a basis for the research of anti-galloping technology of mountain high voltage transmission lines.Simplify the dynamic model of multi-span transmission line dance.Based on substructure method and continuity condition,the non-linear vibration equation of multi-span iced conductor in the whole tension section is established.The non-linear partial differential equation is transformed into ordinary differential equation by Galerkin method.Finally,the theoretical solution of the non-linear ordinary differential equation is obtained by multi-scale method.In order to further investigate the galloping characteristics and the accuracy of theoretical solutions,the non-linear numerical solutions of continuous transmission lines in different modes are given.The effects of structural parameters such as damping,pitch and mode on the numerical solutions are analyzed by using displacement time history curve and phase plane diagrams.The effect of damping coefficient on the attenuation time of non-linear vibration displacement of single transmission line is studied.The results show that damping can significantly reduce the vibration displacement of continuous transmission line.By observing the galloping displacement time history curves of the middle span of the single-span conductor and the three-span conductor,it can be shown that with the decrease of the length of the adjacent conductor,the closer the three-span conductor is to the vibration frequency value of the single-span conductor,and the closer the vibration time and period of the conductor is to the single-span conductor. |
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