Transport Performance and Current Distribution of HTS Current Lead Prepared by YBCO Tapes

High-temperature superconducting (HTS) current lead has been prepared by the trifluoro acetates-metal organic deposition (TFA-MOD) processed YBCO tapes. The YBCO tape has higher critical current density J c and better magnetic property than the Bi2223 tape. Furthermore, the thermal conductivity of the YBCO tape with a thin Ag layer is much lower than that of the Ag-sheathed Bi2223 tape. The critical current of the YBCO tapes ranges from 150 to 180 A in liquid nitrogen and self-field. A current lead is composed of eight bundles stacked by two YBCO tapes (16 tapes), Cu end caps, and a pair of stainless-steel boards. Rogowski coils and Hall sensors used for estimation of current distribution are attached on each YBCO bundle. The transport current of 1.6 kA was carried with no voltage on every YBCO tape at 77 K. Although voltage of several tens of microvolts on some YBCO tapes appeared, transport current of 1.8 kA was successfully carried with no quenching. The voltages between the Cu cap and YBCO tapes almost linearly increased with increasing transport current, and they range from 0.75 to 0.93 mV and 1.02 to 1.21 mV at 1.8 kA, respectively. The low voltages correspond to 0.42-0.52 μΩ and 0.57-0.67 μΩ. The low contact resistance results in low joule heating at Cu joints. The current calculated by Rogowski coils in eight bundles varies from 137 to 355 A at 1.8 kA and sweep rate of 800 A/s. Therefore, the imbalance among eight bundles is evaluated to be 218 A. The current of eight bundles calculated by Rogowski coils sums up to 1808 A, which is the slight difference of 8 A in comparison with transport current of 1800 A. Rogowski coils and Hall sensors are effective at evaluating of current distribution for current lead.