Junke Han

DYNAMIC RESPONSES OF TRANSMISSION TOWER-LINE SYSTEM UNDER ICE SHEDDING

Ice shedding from conductors may easily induce electrical and mechanical accidents, which cause a serious threat to the safe operation of transmission lines. In this paper, a 3D finite element model of tower-conductor-ground wire-insulator system was established in ANSYS, and the dynamic responses of ice shedding under different cases were analyzed for a transmission tower-line system. The computed jumping heights are in excellent agreement with the experimental values of a two span conductors model. Many variables were considered in the ice-shedding simulations that include tower-line coupled effect, phase combination of the ice-shedding conductors, 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 of jumping heights, loads at the end of insulators and the forces of transmission tower were studied. Ice-shedding simulations of an actual 500 kV transmission line section which experience failure under ice shedding in 2008 were performed. The results show that stress ratios of members at the tower head under design ice thickness exceed the limiting values when the amount of shedding ice is large. For ice shedding at the top phase conductors, the jumping height and unbalanced tension at the end of insulator can be reduced by applying interphase spacers in triangular arrangement. The tower is in a safe state under the load of the design ice thickness. In order to prevent ice-shedding accidents, interphase spacers should be used, and the weak members at the tower head should be strengthened according to the calculated load values at the end of insulators.

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.

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.

Analysis of Overall Stability and Local Stability of Legs on UHV Transmission Steel Tubular Tower

The overall stability and local stability of legs on UHV transmission steel tubular tower are controlled by the slenderness ratio and the diameter-thickness ratio of steel bar respectively. 8 typical steel tubular towers with double circuit transmission lines on the same tower in 1000kV transmission project of Anhui Province – Shanghai (the 1000kV Huainan to Shanghai transmission line, the PROJECT as called hereby in this paper) are chosen to set up the finite element model of beam-bar mixed element and calculate the stress of legs under consideration of the effect of bending moment of bar end. The result shows the effect degree of bending moment of bar end to the stress of legs is be closely related to its slenderness ratio. The law between slenderness ratio and stress is obtained by calculation and analysis. The local buckling will occur when the diameter-thickness ratio of round section of steel tubular tower is beyond a limit. Basing on this analysis result and comparison between the domestic design standard and the foreign design standard, the value of diameter-thickness ratio of round section of steel tubular tower is suggested. This study result provides references and proofs for the structural optimization of UHV Transmission Steel Tubular Tower.

Study on the Application of Weathering and Cold-Formed Steel in Transmission Tower

Application of weathering and cold-formed steel in transmission lines can reduce steel consumption and environmental pollution. Some advances in studies on the weathering and cold-formed steel in transmission tower are introduced. Firstly, corrosion-resistant tests of weathering steel samples under different simulating technical atmospheres were carried out separately for 240 hours. It shows that the corrosion degree of joint samples is higher than that of single chip samples, and the corrosion-resistant performance of weathering steel is superior to common carbon steel. The corrosion-resistance of weathering steel meets with the requirement of transmission tower. Secondly, experiments and finite element analysis for cold-formed angles and a 220 kV prototype tower were completed, the stability coefficient fitting curves as well the modification formulas of slenderness ratio for cold-formed members were determined. Ultimate loads calculating by the fitting curve were well agreed to the experimental values, especially for the members with small slenderness ratios. Weight of cold-formed steel tower can be reduced by more than 5% percent after considering the strength enhancement. Cost of weathering and cold-formed steel transmission tower is nearly equivalent to that of hot-rolled steel tower with hot galvanizing. So application of this new style steel can bring great social effects and economic returns. The research results provide important reference to the application of weathering and cold-formed steel in transmission tower.