Design of 22-kV 10-kA HTS Triaxial Superconducting Bus

A 22-kV 10-kA HTS superconducting bus was designed and manufactured with YBCO superconducting tapes. A triaxial configuration was adopted to minimize the ac loss of the cable without shielding layer. The YBCO tapes were prepared by a TFA-MOD (trifluoroacetic acid-metal organic deposition) method on the substrate manufactured by a sputter-IBAD technique. First, bath-cooling the completed cable down to 77 K with liquid nitrogen in atmospheric pressure, we observed the current-versus-voltage characteristics. The critical current I
_c
of each phase exceeded 3 kA. The dielectric breakdown test between the phases and against the earth was also carried out at 77 K in atmospheric pressure. The lightning impulse withstand level of ±125 kV and the withstand level of AC excess voltage of 50 kV for 1 min were verified. The partial discharge was not also observed for AC excess voltage. Liquid nitrogen flow was simulated. The pressure loss was only 60 kPa, which was small enough compared with the pumping power of 0.6 MPa for circulating liquid nitrogen.