Fengli Yang

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.

Simulations for tower collapses of 500kV Zhengxiang transmission line induced by the downburst

The current paper investigates a destructive accident of Zhengxiang transmission line, in which there was six-tower collapse that might be demonstrably conducted by the downburst gust. Based on the dynamic stress analysis of tower members under the strong wind, tower collapse procedure is simulated by finite element method. Finite element method together with material nonlinearity, large deformation, contact, etc, is adopted to model the accident transmission line. Implicit and explicit method are both incorporated for the time integration in the dynamic analysis. Since the accident downburst gust have not been detailedly observed, the strong wind model and the simple gust model are experientially specified as the load boundary condition. The calculation results show that, maximum stress values of some tower members exceeds design values under the specified strong wind and then may overload tower members. With the specified downburst load, tower collapses will occur, and the broken-down tower in the simulation is very similar with real one. The introduced numerical models are effective and available to calculate the transmission line accident further.

Study on effect of grid meshing on simulation of flow field around an equal-leg angle member in transmission tower

This paper adopts three different grids to conduct numerical simulation of flow field around an angle member by CFD. The two-dimensional incompressible Navier-Stokes equation is solved. The pressure velocity coupling adopts the SIMPLE algorithm and the pressure discretization adopts the standard algorithm. Both the momentum equation and turbulence model adopt the second-order windward scheme, and the time term adopts the second-order implicit scheme. The aerodynamic coefficients of angle member and the flow field are obtained by different grids, and through comparison, it is found that the grid mode has a very small impact on the CFD results, and the differences between different grid modes can be ignored. In respect of CFD simulation of flow field around angle member in transmission tower, it is recommended to adopt the partitioned structured grids and the partitioned mixed grids in order to enhance the simulation ability of the grid under multiple working conditions. If the angle member is irregularly s...

Dynamic responses of the conductors in transmission lines under two typical impact loads

Impact loads from ice shedding and broken conductors are common for transmission lines in accreted ice zone, which can bring threaten to the safe operation of the transmission lines. Dynamic analysis of the conductors in transmission lines under two typical impact loads were carried out. Firstly, a finite element model of seven span conductors in transmission line was established in general software ANSYS. Secondly, a time history of the input loading was proposed for the ice shedding load case. Dynamic responses of jumping heights and the reaction forces at the end of insulators were calculated by the implicit dynamic analysis. Some variables were considered in the ice-shedding simulations that include thickness of the accreted ice, length of the ice-shedding span as well as elevation difference. Influences of all the variables on the dynamic responses under ice shedding were studied. Thirdly, the broken load case can be realized by birth-death element method in ANSYS. Stiffness of the broken conductor or insulator element was changed to be a near zero value in a very short time. Dynamic responses of displacements at the broken points, tension forces of the conductors and the reaction forces of the insulators were obtained. Lastly, based on the analysis results, the impact factors under ice shedding and broken conductor load cases were determined, which provide important reference for the design of transmission lines in accreted ice zone.