A New Theory for Calculating the Torsional Stiffness of Multi-Bundled Conductors

The torsional stiffness of multi-bundled conductors is affected by multiple factors, such as the rotation angles with non-linear distribution along the span, the sag, and the tension changes of sub-conductors during rotation. A mechanical model of torsion for multi-bundled conductors was established, and theoretical formulas describing the relationship between torque, rotation angle and torsional stiffness were derived. The results calculated by the new theory match well with those of the finite element method. The formula is simple and easy to apply in engineering design. Then, the inconsistencies in torsional stiffness calculated by Nigol et al. theory were analyzed in detail. Finally, the impacts of initial tension and span length changes on the rotational characteristics of bundle conductors were explored. This study indicates that: 1) The non-linear distribution of rotation angles along the span can significantly affect torsional stiffness. 2) The sag and the changes in tension of sub-conductors during rotation affect the non-linear segment of the torque-rotation angle curve, but have almost no effect on the linear segment. 3) Increasing initial tension or decreasing the span length with a fixed length of sub-span can effectively enhance the initial torsional stiffness of the conductors and suppress rotation to a certain extent.