Comparison of transport AC losses in an eight-strand YBCO Roebel cable and a four-tape YBCO stack

Transport AC losses in a 8/2 YBCO Roebel cable and a stack composed of four YBCO tapes were compared. The normalized transport AC loss in the Roebel cable was smaller than that in the stack. This is the first experimental demonstration of advantage of Roebel cables over stacks with and without transposition. This is important for 2G HTS power applications where transport AC loss is dominant. The transport AC loss in a short length of 8/2 YBCO Roebel cable, (i.e., with 8 x 2 mm width strands) is measured. The results are compared with those in a stack composed of four 4 mm-wide YBCO tapes carrying the same current in each tape to verify the advantage of Roebel cables over vertical stacks in terms of transport AC loss. The vertical separation between the superconductor layers in the Roebel cable and the stack is made the same to facilitate comparison. The normalized transport AC losses in the cable are smaller than those in the stack. This is a clear demonstration that Roebel cable is advantageous over stacks with and without transposition of the tapes composing the stacks. Results from a numerical calculation are in accord with the experimental results.