Effect Of Bolt Pre-tightening Force On Strength Of Transmission Line Tower

As an important life-line engineering in power grid in China, over-head transmission lines are responsible for the transmission, regulation and distribution of electricity. The normal operation of transmission system is directly related to the realization of the function of the whole power system. Failure caused by the icing and ice-shedding of transmission lines has always been one of the natural disasters which threaten the normal operation of power system. In recent years, the accident of conductor rupture or tower collapse of transmission line tower system happens from time to time, which has attracted wide attention of the design department and research institutions, and the reasons or mechanism for tower damage have become a research hotspot.This paper takes No. 61- No. 66 actual line section of Sichuan 500 k V Yue-Pu general double circuit as the research object, by use of finite element numerical method, firstly, we established six tower-seven span tower-line coupling system finite element model, and numerically simulated the effect of the impact of conductor on the stress and deformation of tension tower under different load cases of ice-shedding. The analysis for the collapsed of No. 65 tower in the actual section shows that the stresses in the dangerous zone are always less than the allowable stress when using beam-truss model, which indicates the destruction of tower is related to structural details. Therefore, we established a mixed tower model of entities and girder while considering the details of the structural link, bolt pre-tightening force and the clearance between bolts and screw holes. By use of the model, we simulated the stress and deformation under load case of icing, through the comparison of the stress and displacement of typical position other than dangerous zone of tower and the analysis results of tower-line coupling system, we verified the validity of model and the method.Make use of this mixed tower model, we simulated the effect of distinct level of bolt pre-tightening force on the bolt slippage and the stress of tower components under different load cases. It is concluded that smaller bolt pre-tightening force will give rise to larger slipping and structural stress, therefore, insufficient bolt pre-tightening force probably be one of the main reasons leading to tower collapse.The analytical method presented by this paper provides an effective way for the analysis of causes of transmission tower failure, and the results of numerical simulation is of valuable reference for the improvement of tower design.