Evaluation of bending stiffness of transmission line conductors

Abstract

Cables are made of helically wound wires and have a wide range of engineering applications. This thesis considers the use of such cables in overhead electrical power transmission lines. The loading on such cables is generally axial pull or tension and torsion. The oscillation of the overhead power transmission lines due to the wind or static bending in any applications, newlineintroduce an additional bending load on such cable assemblies and are subjected to varying newlinebending curvatures and results in reduction in bending stiffness. The effective stiffness of the cable assembly in its bent state varies widely between two extreme newlinebehaviours a monolithic infinite friction state offering the maximum stiffness and a newlinecompletely loose wire zero friction state offering the minimum thickness. Due to the wide variation of this extreme values, the estimation of the cable stiffness at any intermittent stage of bending has been quite challenging and is under continuous refinement. Though many mathematical models are stipulated in the last seven decades in cables, seldom they consider the influence of wire forces and moments about its normal, bi-normal, and axial directions together, in any analysis and evaluated the cable response. newlineThe dominant wire force and moments about the axial directions were never missed by many newlineauthors. Though the global behavior of the cable apparently seems to be all right even with the omission of some forces/moments, the mechanism of its constituent wires needs a fully proven scientific explanation that predicts the local behavior also correctly. The ultimate response of the cable will be complete when accurate theories are attributed for the global and local newlinebehaviours. Hence, this research work addresses the complete mechanics of the helically wound cables and considers the influence of wire forces and moments, in all the three directions, together in the newlineanalysis and evaluates the cable response.