Unbalanced tension analysis for UHV transmission towers in heavy icing areas

Unbalanced tension is one of the most important controlling loads for the design of transmission towers in cold regions. It can be caused in some cases including non-uniform accreted ice, broken wires, ice shedding and galloping. Firstly, for the comparison of the unbalanced tensions and the inclinations of the suspension strings, the FEA method and the constant conductor length method were applied. The results by two methods are approximately well agreed. With the consideration of some design parameters of the transmission line, a seven continuous span FEA model of conductors and insulators was established. Secondly, under different load cases, the tensions and the unbalanced tensions of conductors were analyzed for the UHV suspension tower and tension tower in heavy icing areas. It shows that the load modes and the eccentricity of the accreted ice, as well as the wind velocity only have little effect on the unbalanced tensions. The transforming density method and 10 m/s of wind velocity are proposed for the analysis of the unbalanced tensions. When there are no elevation difference and span difference, the unbalanced tension of the UHV suspension tower increases with the ice thickness, the span length and the icing rate, and the calculated values for different ice thickness are lower than those of regulations. With the increasing of the elevation difference and the span difference, the ratios of the unbalanced tensions with and without elevation difference as well as span difference increase. However, the ratios of the unbalanced tensions with and without elevation difference as well as span difference decrease with the ice thickness. For tension towers, variations of the elevation difference and the span difference have little effect on the unbalanced tensions. Lastly, the calculated values of the unbalanced tension percentages of UHV transmission towers were compared with those of applicable regulations, some suggestions on the unbalanced tension values were proposed.

► FEA model of UHV transmission line in heavy icing areas was established.
► Parametric study on the unbalanced tensions was carried out.
► Unbalanced tension values were determined for the UHV transmission towers.