Analysis on Unbalanced Tension Caused by Ice-Coating on Conductors of UHV/EHV AC Multi-Circuit Transmission Lines on the Same Tower

Based on the types of conductors and ground wires and the parameters of insulator strings for EHV/UHV AC multi-circuit transmission lines on the same tower,an finite-element model of line-insulation string coupled system is built,and the law of non-uniform ice-coating varying with the number of strain spans in one section as well as the impacts of height difference among different positions,where conductors or ground wires are suspended,on unbalanced tension caused by non-uniform ice-coating are analyzed,and a method to analyze and calculate unbalanced tension caused by non-uniform ice-coating is given.The law of unbalanced tension caused by non-uniform ice-coating at the positions suspending conductors and ground wires for UHV/EHV AC multi-circuit transmission lines on the same tower varying with ice-coating rate is analyzed and quantitative calculation results are given.On this basis,a three-dimensional finite-element model for the coupling among towers,lines and insulator strings is built,and using this model the impact of tower deformation on unbalanced tension caused by non-uniform ice-coating is analyzed,and the contrastive analysis of calculation results by the three-dimensional model with the results calculated by finite-element model of line-insulation string coupled system is performed.Based on finite-element analysis,the selected percentage values of unbalanced tension caused by non-uniform ice-coating for the suspension tower,conductors and ground wires of UHV/EHV AC multi-circuit transmission lines on the same tower are given,and with regard to general situation the selected percentage value for conductor is 10%,the selected percentage value for ground wire is 20%.When economy is taken into account,different percentage value of unbalanced tension can be selected for conductors and ground wires of the transmission lines belonging to different voltage grades on the same tower: the selected percentage value for conductor belonging to 1 000 kV transmission line is 7%,and the selected percentage value for conductor belonging to 500 kV transmission line is 10% and that for ground wire of 500 kV transmission line is 20%.