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.

I. Introduction

According to the restriction of the terrain characteristics and the corridor conditions, transmission lines usually pass the goaf of coal mine. There are some transmission lines with an electrical grade not higher than 500 kV passing the goaf of the coal mine in China. Affected by the surface settlement of the goaf, the foundation of the transmission pole and tower will be destroyed by settlement, inclination, or slip. Then, with the variation of the leg opening and height difference of the tower legs, the tower structures will bear high additional loads, and part of the body or the entire body of the tower structure may break down. Deformations of the foundation have introduced a serious threat to the safe operation of the power grid.