Strain analysis of the superconductor REBCO tape of CORC cables under winding, bending and twist deformations

Abstract

Conductor on round core (CORC) cables are superconductor rare earth-barium-copper-oxide (REBCO) based conductors that allow for high operating currents and have been becoming one of the most flexible high temperature superconducting (HTS) conductors to date. Nevertheless, due to the brittle nature of superconductor REBCO ceramics, the critical current exhibits a sensitive strain dependence, i.e., the critical current varies closely with strain, and especially raises a significant degradation once the strain exceeds a critical value. And, due to the complex deformation of tape winding and after cable stranding, firstly there is a practical challenge that how to accurately estimate the axial strain of the superconductor tape of cables under various deformations. In this paper, we developed the analytical models that can be used to accurately calculate the axial strain of the superconductor tape of CORC cables under the practical conditions of tape winding on the cable core, the cable bending, and twist deformations for stranding. The analytic model was validated by comparing the analytic result both with FEM numerical result and experimental data that the critical current of the superconducting tape varies with the core diameter of CORC cables. Further, on the analytic models, the axial strain, and the dependence on the core diameter and winding angle, the bending diameter, and the strand pitch were obtained respectively for CORC cables under tape winding, cable bending, and twist deformations. Particularly, the critical parameters, which are here defined at which the axial strain of the superconductor layer just reaches the critical strain, such as the critical core diameter, critical bending diameter, and critical pitch were determined. Thus, the analytic study of the strain of the superconductor REBCO tape of CORC cables will be helpful for CORC cables processing and further the design of high-level superconducting coils and magnets.