Zifu Zhang

Study on the Limited Values of Foundation Deformation for a Typical UHV Transmission Tower

The tower foundation above the goal of the coal mine is easily deformed, which causes a serious threat to the safe operation of ultra-high voltage (UHV) transmission lines. In this paper, the finite-element model of a typical 1000-kV UHV ac transmission tower was established in general software ANSYS, and the axial forces of the members as well as their variation trends were analyzed under different load cases, which include foundation settlement, slip, and inclination combined with normal design cases. Limited values of the foundation deformation under different cases for the analyzed tower were determined. It shows that the limited values of longitudinal deformation, transverse deformation, nonuniform settlement, and horizontal slip are decreased, in turn, with the same external loads. The limited value of the foundation deformation under 60° wind is the minimum, which is the control load case of the foundation deformation. The limited value of nonuniform settlement through computation is lower than that of the current regulation, and it is dangerous to evaluate the stress state by the regulation method. In the righting process of the tower with foundation deformation, the axial forces of the members are not more than than the critical bearing capacities except the horizontal slip case, and the tower is in a safe state.

Dynamic responses analysis and disaster prevention of transmission line under strong wind

Dynamic analysis of a typical transmission line section under strong wind was carried out. Firstly, according to the design conditions of the typical transmission line section, a three dimensional finite element analysis model of cup tower-stay frame tower-conductor-ground wire-insulator system was established in ANSYS. The initial tension force of the conductors was applied by the cooling method. Before the wind-induced vibration analysis, the form-finding analysis of conductors under self weight was carried out. Secondly, time history of the impulsive wind velocity was generated by spectral representation method. Time history of the impulsive wind velocity can be obtained by Fourier transformation in MATLAB program. The average wind pressure is applied to the tower line system by static method, and the impulsive wind pressure is applied by transient dynamic method. Thirdly, for the wind load case of design velocity, the wind-induced responses of the typical transmission line section were analyzed. Effect of the structural damping was considered by Rayleigh damping coefficients. Nonlinear transient analysis was employed for the wind-induced dynamic analysis of transmission line system. Under different wind velocities and directions, some wind-induced responses were obtained, which includes the tension forces of the conductors and the ground wires, axial forces of the towers, and the tension forces of the stray frame tower. Lastly, based on the analyzed results, the prewarning wind velocity for the typical transmission line section was determined. Some strengthen suggestions for the tower design in the strong wind zone was presented.

Tower Destruction Mechanics of Overhead Transmission Lines and Prevention Technologies in Ice Disasters

Some advances on tower destruction mechanics of overhead transmission lines and prevention technologies in ice disasters are introduced. Firstly, based on the numerical and experimental study on the tower-line system with ice-shedding and broken of conductors, dynamic responses of the tower-line system were obtained, and the unbalanced tensions as well as the uplift loads were proposed. Secondly, study on the bearing capacity of K type joints with an included angle less than 30 degree was completed. The first ultra high voltage (UHV) steel tubular cup type tower in the world was designed for transmission lines in heavy icing area, and the prototype test was carried out in the UHV tower test station. Thirdly, the bearing capacity and the destruction modes of transmission towers with galloping conductors were studied. A practical calculation method of the galloping loads was obtained. A constructional measure realized by the bolt strengthen technology were proposed for the transmission towers in the galloping area with high intensity. Lastly, the structural reinforcement technologies of the transmission towers after ice disaster were developed, especially for the enhancement of design standards and reinforcement technology for main members of transmission towers. Keywords: Transmission tower; Accreted ice; Load characteristic; Destruction mechanics; Reinforcement.