Development of a 10 m long 1 kA 66/77 kV YBCO HTS cable with low AC loss and a joint with low electrical resistance

We have developed high-T(c) superconducting (HTS) cables using YBCO tapes. A 10 mm-wide YBCO tape was divided into five strips using a YAG laser to reduce AC loss. A 0.3 m conductor and a 1 m conductor were fabricated achieving AC losses at 1 kA(rms) and 50 Hz of 0.054 W m(-1) and of 0.048 W m(-1), respectively. Based on the successful AC loss reduction in the 0.3 and 1 m conductors, we fabricated a 10 m HTS cable with a three-layer HTS conductor, electrical insulation, and a one-layer HTS shield. The AC loss in this 10 m HTS conductor was 0.090 W m(-1) at 1 kA(rms) and 50 Hz. An HTS cable joint was designed and fabricated that included a three-layer HTS conductor and a one-layer HTS shield. Joint resistance of 5.2 n Omega for the HTS conductor and that of 10 n Omega for the HTS shield were achieved. The HTS cable joint was compact and had sufficient withstand voltage properties for 66/77 kV. In addition, we also confirmed the efficiency of joint construction. Moreover, a 20 m long HTS cable was successfully constructed and tested in January 2008. This HTS cable consisted of two 10 m HTS cables and the HTS cable joint. One 10 m HTS cable using HoBCO was made by Sumitomo, and the HTS cable joint and the other 10 m cable using IBAD YBCO were made by Furukawa and Chubu. The electrical resistance of the HTS cable joint was less than 10 n Omega, and the 20 m HTS cable including the joint withstood an over-current of 31.5 kA(rms) whose duration was 2 s.