| The electric power industry plays an important role in guaranteeing the reliable power supply for the national economy.The long-span turning-angle transmission tower is an important part of long distance transmission lines.Its strength,stiffness and stability under various loads is related to the safe operation of the entire transmission network.The strength and stiffness of a 220 kV turning-angle transmission tower is analyzed in this thesis.Firstly,the ANSYS finite element software is used to establish the system model of a single tower and a turning-angle tower-line system with three towers and two lines.The natural frequencies and modes are obtained basing on the finite element analysis.The results show that the natural frequencies of the turning-angle tower-line system are very dense.The torsional modes rarely occur,and their frequencies are lower than those of a single tower.Then,the static strength of the single tower is analyzed under the conditions of strong wind,covering ice and disconnection.The displacement response,Mises stress,node displacement and element axial stress of each main structure under various conditions are respectively studied.It is found that the node displacement of the main structure increases with the increase of its height.The maximum of Mises stress occurs mostly at the height of 27 m,the position where the inclination of the main structure changes.Under the strong wind conditions,the node displacement and unit axial stress as the main structure will increase with the increase of the wind direction angle when the wind direction angle is within 0-90 degree.Under the covering ice condition,the displacement difference of the main structure nodes is obvious,and the difference of the element axial stress decreases with the increase of the wind direction angle.In the case of the disconnection,the difference of node displacement decreases with the increase of height.In different cases of disconnection,the element axial stress of the main structure will change from tension stress to compression stress.After the steady wind load is simulated by using the harmonic synthesis method in MATLAB software,the wind-induced vibration response of a single tower and tower-line system for turning-angle transmission is analyzed.The results show that the transmission tower in the tower-line system produces bending and torsional vibration along the wind direction.The lateral displacement time history of the node fluctuates around the displacement mean value.The longitudinal displacement meanvalue of the node increases with the increase of the node height,and the longitudinal displacement mean value in the inner side is larger than that in the outer side.Finally,the seismic response spectrum analysis and time history analysis are carried out for a single tower.The maximum of stress and displacement of the transmission tower will increase with the increase of seismic intensity.Under the same seismic intensity,the stress and displacement values caused by 45 degree seismic excitation are larger than those caused by the transverse and longitudinal seismic excitation.The displacement trend for the top node of the transmission tower is affected by the acceleration of seismic wave,and it will converge rapidly to the maximum displacement and then gradually decrease. |
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