Distribution of electrical conductivity in the stranded CD cable

What is it about?

Our work focuses on the analysis of the electrical behaviour of conductive cores of electric cables, and more specifically on their total electrical resistance. The analysis will be conducted based on several parameters related to the design and manufacturing processes. The electrical conductors manufacturing process involves many steps such as drawing, wiring, compaction, extrusion, assembly, etc. This study focuses on the analysis of a cable called 1 + 6, performed after twisting and compaction. During manufacture of the cable the wires are subjected to traction and torsion forces, compression forces due to the compaction die, to the tangential forces generated by the friction between the compaction die and wires of the outer layer. All these parameters affect the metallurgical condition of the material. To our knowledge, the existing models based on static geometry neglect the actual deformations of wires and electrical conditions in the contact areas. In a concentric cable with a conventional composition (1 + 6 + 12 + ...) there is not enough space to place all wires. However, as the material (copper or aluminium) are quite elastic, the contact pressures generated during the manufacturing process will change the shape of the wires and reduce their dimensions.

Featured Image

Why is it important?

The originality of this work consists in taking into account the deformed geometry of the conductor and the uneven distribution of the resistivity within a filament. Knowing that all wires constituting the cable undergo plastic deformation by cold working during the manufacture, their influences on the electrical conductivity of the material will be analysed. These plastic deformations are due to the formation, multiplication and movement of mobile line defects in the crystal lattice of the metal called dislocations. The growing number of dislocations produced during plastic deformation and their interaction with each other (or with impurities) leads to reduced mobility. This results in a hardening of the crystal structure of the metal.. It also causes a decrease in the grain size and increasing the number of grain boundaries in the metal structure. Furthermore, defects in the crystal lattice of the metal are obstacles for the electric charge carriers (electrons). These variations cause a degradation of the electrical conductivity of the material, but also a non-homogeneous distribution thereof in a wire section. We have developed a new method to take into account the effect of localized hardening on the inhomogeneous distribution of electrical conductivity in the distorted structures of the conductor. To achieve this goal, we have implemented a mechanical-electrical coupling strategy (weak coupling) using the program Abaqus. This requires the use of a specific behaviour law material, for connecting the mechanical parameters to electrical parameters. First we present an experimental study to determine the behaviour of law relating the conductivity to the parameters describing the hardening of the material, such as residual stress fields and / or field of plastic deformation. In a second step, the coupling strategy is described by considering a simple example of a plate deformed during the traction. A comparison of the obtained results with the measurements is conducted to validate the models.