Transport AC loss characteristics of a nine strand YBCO Roebel cable

Abstract

Transport AC loss in a short length of 9/2 YBCO Roebel cable (nine 2 mm wide strands) ismeasured. The AC loss data are compared with those in a 5/2 YBCO Roebel cable (five 2 mmwide strands) as well as that in a single strand. All the strands composing the cables andthe single strand are insulated and cut from the same stock material. The validity of themeasurement method was reconfirmed by results at a range of frequencies. At a wide range ofIt/Ic, the normalized AC losses in the Roebel cable were around 6.2–6.7 times of those in the singlestrand. This is less than the nine times predicted for a tight bundle of nine conductors. Thenormalized transport AC losses in the 5/2 Roebel cable are much smaller than those in the 9/2Roebel. This should be due to larger superposition of magnetic field in the 9/2 Roebel. TheIc of the 9/2 and 5/2 Roebel cables is determined by serial connection of the strands. Thiseliminates the effect where differing resistances in the current terminations causeuneven current sharing between strands when the strands are connected in parallel.