Electro-mechanical analysis of Roebel cables with different geometries

For future fusion applications, superconducting motors and generators, HTS Roebel cables with high effective current densities are desired. Due to the enormous Lorentz forces of fusion magnets or the centrifugal forces of rotors, these cables must also be able to withstand high mechanical loads. Coated conductor material can sustain high tensile loads; however, the meander structure needed for Roebel assembled cables concentrates mechanical stress at the crossing sections. This weakens the tape mechanically and makes it prone to failure in these regions. The increase in mechanical sensitivity depends on geometric parameters such as angle, width and inner radius of the Roebel structure and can be reduced by an optimized geometry. In this paper Roebel cables with varying geometries were investigated mechanically and electrically. Firstly, different meander structure geometries were analyzed using 3D finite element method (FEM) models to evaluate their resistance to tensile loads and the minimal possible transposition length. Secondly, the electro-magnetic properties of the 2D cross section of a Roebel cable were investigated with FEM simulations. These simulations were used to derive an improvement of the meander structure which permits almost the same twist pitch, but increases the mechanical stability and the current carrying capabilities of the whole Roebel assembled cable. (paper)