Current carrying capability of HTS Roebel cable

We have developed a numerical technique to estimate the current carrying capability of HTS Roebel cable composed from coated conductor strands. The influence of self-field on the critical current density is studied computationally for a Roebel cable using a realistic field and angle dependence behaviour of critical current. The computations are carried out for N/2 (number of strands/strand width in mm), and N/5 Roebel cable for N = 2–15. The local current distribution in each strand satisfies the self-consistent criteria J = Jc(B(J)) except for a small region where the current density is set to zero to maintain the condition of equal currents in all strands. The variation of critical current with vertical and horizontal separation between the strands is also investigated. Results are compared with the measured values of critical current for some of our cables. The comparison shows an error of up to 10% which we attribute mostly to the model not accounting for the spread in Ic values of the constituent strands.

Research highlights
► We present a computational method to assess self-field critical current in Roebel.
► Both perpendicular and parallel magnetic field play role to in this computation.
► A current-free rather than a flux-free region is obtained in centre of stack.
► Critical current increases with separation between the strands.
► Critical current of the Roebel cable is higher than that of a single stack of tapes.