The Galloping Mechanism Of Iced Transmission Tower-Line System And Analysis Of Its Response

The galloping of iced transmission lines is a self-excited vibration with low frequency, large amplitude, and it is not only have horizontal and vertical motion, but also has twisting motion, galloping is one of the important factors for damaging iced transmission tower-lines. The law of coagulated ice on power transmission conductors, the movement patterns and instability mechanism of galloping under wind load has important practical value and theoretical meaning, which has become a difficult and hot issue in electric field of science. Snow and ice disaster happened frequently and distributed widely in the world, which brought great threat to security operation and development of transmission network, such as electric power transmission from west to east. In this paper, a typical transmission tower-line system was selected to analyze the galloping characteristics through theoretical analysis,numerical simulation and wind tunnel test, which mainly analyzed the aerodynamic characteristic of iced conductor, galloping mechanism and galloping response of iced transmission lines under wind load, which provided a good reference for anti-galloping of transmission system. The main contents in this thesis are as follows:1. Numerical simulation on the aerodynamic force of iced transmission lines. This paper researched the effect of wind attack angles, wind speed and ice thickness on the galloping of iced transmission lines, and aeroelastic models of single conductor with crescent, D-shaped and fan-shaped sections were set up, and the aerodynamic characteristics of iced single conductor were simualted. The flow field information was analyzed for iced single conductor and bare conductor, and the whole process of the wake of vortex shedding had been researched, and the difference of field information between iced single conductor and bare condutor was found. The variation of aerodynamic coefficient with D-shaped and fan-shaped iced conductors was more complex than crescent section, which were more likely to gallop than the conductor with crescent section. The aerodynamic characteristics of twin-bundled and quad-bundled subconductors were analyzed, which demonstrated sub-conductors at downstream were seriously influenced by the ones at the upstream, with the increase of the number of sub-conductors, and the wake flow effect of each sub-conductors was more complicated, the bundled conductors were more likely to gallop than single ones. Response surface method was applied to analyze the aerodynamic coefficient affected by wind speed, wind attack angle, and ice thickness, and the formulas of Den. Hartog and Nigol were derived with wind speed, wind attack angle and ice thickness.2. The development and application of a new spatial two-node catenary element. Transmission line system has the characteristics of cable structure, in order to analyze the linear and nonlinear behavior of cable structures under various loads, based on its mechanical characteristics, this paper presented a spatial two-node catenary cable element model(STCCE), which can be used to analyze the nonlinear effect of cable structures. Based on the analytical solutions of elastic catenary, the tangent stiffness matrix was derived, and the stiffness matrix and the internal force vector were calculated using an iterative algorithm, and the nonlinear behavior was analyzed using the new model(STCCE) under static and dynamic loading. The Newton-Raphson method was applied to solve the structural balance equation for the nonlinear static analysis. An incremental iterative method, based on the Newmark direct integration and Newton-Raphson methods, was used for nonlinear dynamic time-history analysis. The accuracy and reliability of the STCCE were verified using numerical analysis. It provided a new algorithm for galloping of transmission system.3. Galloping resonpse analysis of transmission lines based on spatial two-node catenary element. The bending stiffness and the torsional stiffness were assembled into the stiffness matrix of two-node catenary element, and the mass matrix, the stiffness matrix and the damping matrix of iced transmission conductors were constructed. The dynamic equations with three degrees of freedom was derived, which had not only interactions of the vertical and horizontal, but also the torsional movements. The incremental iterative method based on Newmark direct integration method and Newton-Raphson method were used for solving dynamic nonlinear motion, the analytical solution in time-domain of iced transmission lines under different wind speed was got. In order to find out the critical wind speed of galloping, the Hurwitz criterion was applied to judge the instability condition of galloping, and the cirtical wind speed was also solved by Hurwitz criterion. By analyzing the response of galloping affected by wind speed, span and sag, the results showed that the tesion of iced transmission line periodical changed with time.4. The galloping response of large-span iced bundled conductors. Establishing the finite element model of iced bundled conductor, considering the torsional stiffness of bundled conductor and aerodynamic coefficient of each subconductors, calculating the galloping response of twin and quad bundled conductors at 10m/s wind speed, the results showed that the amplitudes of along wind direction and cross wind direction were larger than that of single conductor, because the spacers limited the twist of conductors, and the torsional dynamic response was not larger than that of single conductor. Considering three joint types of conductors and spacers: hinge joint, rigid joint and semi-rigid joint, if the conductors were connected with spacers by rigid joints, the galloping amplitudes of three directions were lager than hinge and semi-rigid joints, and it was smallest by using hinge joints between the subconductors and spacers.5. The galloping response analysis of iced transmission tower-line system. The form-finding of single-span and multi-span cable was researched under its own gravity, uniform ice and non-uniform ice load. The finite element model of transmission tower-line system was established. By simulating the random fluctuating wind field, the galloping response at intermediate node of iced transmission tower-lines was calculated under fluctuating wind. By simulating the random fluctuating wind field, the galloping response at intermediate node of iced transmission tower-lines was calculated under fluctuating wind. By analyzing the axial tension of the joint at tower and insulator under fluctuating wind field, the imbalance tension between adjacent span mainly transmitted through the insulator string. The galloping generated by fluctuating wind was lager than the average wind. The galloping of intermediate span conductor was tranmitted by insulator string, driving adjacent span conductor galloping.6. The wind tunnel test of iced transmission lines galloping. According to the similarity coefficient of aeroelastic models in wind tunnel test, simplified aeroelastic model of transmission tower-line system was made. In these cases of different wind speed and wind direction, the galloping response of iced aeroelastic model of transmission tower-lines was analyzed. The results proved that the galloping response was seriously affected by wind direction and wind speed, with the increase of wind speed, the amplitude of galloping response increased gradually, and the existence of critical wind speed was verified. The galloping amplitude of across wind direction was larger than that of along wind direction.