| Overhead transmission line is a lifeline project used to transport,regulate and distribute electric power.The study of wind-induced,loads induced by ice accreting and ice shedding on transmission lines is of great significance.On the basis of an existing cup type transmission line,a three dimensional finite element model of cup type transmission-line tower coupling system is built.Based on finite element software ANSYS,the unit forms on the composition of cup type transmission tower were analysed to obtain the best modeling method.Three towers and four-span coupling system models were established to carry out modal analysis.According to existing norms and numerical analysis method,approximate formulae for calculating basic frequency adapting to cup type transmission tower was fitted out.Models of iced conductors(ground wires)and iced transmission tower suitable for this paper were selected.Three towers and four-span unequal ice-coating coupling system models were established as the added pseudo mass element method to carry out modal analysis,which has provided the reasonable calculation parameters for the dynamic response analysis.Wind load calculation parameters were determined and wind operating modes were selected to carry out wind induced dynamic response analysis on three towers and four-span iced models.By processing the data,the effects of icing on transmission-line coupling system under the effect of wind vibration and the worst wind operating mode were obtained.11 combined operating conditions of ice-shedding conductors(ground wires)were assumed.Using the birth-and-death elements of the finite element analysis software ANSYS facilitated ice-shedding dynamic response analysis of the structures system under each operating mode to obtain the worst ice-shedding operating mode,the failure modes of structural systems and the weak positions of the cup type transmission tower.Studies have shown that the increase of ice load would cause the coupling induction of the transmission to be more obvious.After determining the icing-thickness and the element length,the method of adding pseudo mass element would be used to realize the simulations of ice coating and ice-shedding,as well as the simplified numerical simulation program and the shorter computation time.In the analysis of wind-induced vibration response for iced structural system,the lateral galloping form of conductors and ground wires were basically the same,while the degree of vertical oscillation was different.Due to the impact of ice load,the peak value of displacement response at the transmission tower top was larger and the frequency wassmaller,while the peak value of displacement response at the 1/4~1/3 height of tower was the largest and the vibration frequency was exacerbated.As for the dynamic response analysis of iced structural system due to ice shedding,the vibration modes of shield wires and conductors are quite different.However,in both cases the jump height of transmission line due to ice shedding and the sag of the line were proportional to the ice quality.As for iced transmission tower affecting by impact load and unbalanced tensile force,the longitudinal vibration of tower took predominance and the tower was mainly determined when ground wires were ice-shedding.The comprehensive analysis reveals that the lateral stiffness of iced cup type transmission tower was liable to be damaged under the effect of wind vibration and the strength of the tower principal was liable to be damaged under the dynamic effect of ice-shedding conductors(ground wires). |
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