Study On Wind-induced Response And Stability Of Transmission Tower-line System

With the rapid development of the national economy, science and technology and environmental awareness, electric power industry changes a lot, and HV, EHV transmission mode has become the main development mode of today’s electricity supply. With the escalating of power grid, transmission tower structure is gradually developing toward the high-rise, long-span and the UHV rapidly. Typically, transmission line system with common characteristics such as high-rise tower, span large, flexible is very sensitive to seismic, wind, ice and other environmental loads.The existence of transmission line for tramission tower-line system has impact on the dynamic performance of the tower and the wind induced response.So it is necessary to establish the transmission tower-line model and to research the dynamic characteristics,the response of wind induced vibration and stability under icing load in order to get conclusion that has reference value of theory research and practical application. The main research work of this paper is listed as follows.1) Based on AR model of linear filtering method,consider Kaimal pulsating wind spectrum and apply Matlab to realize simulation of space-dependent pulsating wind speed, and wind load time history samples of transmission tower-line along different heights are further obtained.2) In the finite element analysis software ANSYS, the finite model is established by APDL (Ansys Parameter Design Language) with truss and beam hybrid element, considering the structure and mechanical characteristics of transmission tower. Based on the theory of form-finding for transmission line, the shape of line is completed in ANSYS.Thus the finite element models of a transmission tower, transmission tower coupled with lines and transmission twin towers coupled with three-lines are established. And then, according to the result of modal analysis and contrast of dynamic characteristics among three models, we find that parts of tower below the nominal height is the relatively weak position while the cross-arm section has larger stiffness, that free vibration frequency of the conductor wire is close to grounding wire’s, and that the transmission line has directional influence on the dynamic characteristics of the transmission tower. To be more exact, the longitudinal impact is great, while the transverse almost has no effect. The first-order vibration mode of tower is transverse bending vibration, while the first mode of transmission tower-line system is longitudinal bending vibration. Compared to tower coupled with lines, transmission twin towers coupled with three-line model is to match the reality more exactly, and the result is more credible with relatively small free vibration frequency.3) Grounded on wind load time domain samples in second chapter, the response of pulsating wind induced vibration of a single power and twin towers coupled with lines is calculated and contrasted using Newmark-β method in ANSYS. Conclusion is drawn that compared to the tower, the RMS (root mean square) of displacement of tower-line system increases to some extend,while the RMS of acceleration decreases, which is consistent with the result of wind tunnel test.4) The buckling mode of transmission tower is obtained using eigenvalue buckling analysis under the wind load, icing load and the mixed, and further calculate the minimum buckling load.Considering elastic-plastic materials, geometric nonlinearity, apply the initial defect and analyze its stability under icing load.And the ice thickness leading to instability of tower in the absence of wind and normal wind can be obtained.