Abstract
The AC quench current and AC losses of multi-strand Nb-Ti superconducting cables for S/N type fault current limiter are described. The Cu ratio for S/N type fault current limiter should be zero or less than 0.2, in order to increase normal state resistivity. The resistances of Nb-Ti/Cu-Ni strands with zero Cu content shall be 3.9_??_13.2Ω/m at 10K. A 72-strand 3kA-class cable showed higher AC (50Hz) quench currents with suppression of wire movements. The AC quench currents Iq's of multi-strand cables change with the phase angle difference (θ) between the magnet current and the sample current. A 7.6mm-dia cable from 360 pieces of Nb-Ti/Cu-Ni strands with zero Cu content and resistance of 6.7Ω/m at 10K each, showed Iq's of 4_??_4.5kArms at θ of 0° and 180° and 5.5_??_6.6kArms at θ of 90° and 270° at a bias field of 0.5Tpeak, and showed those over 8kArms at θ of 0° 90°, 180° and 270° at a bias field of 0.2Tperk or under, both at a frequency of 51.41Hz. On the other hand, A 7.6mm-dia cable from 360 pieces of Nb-Ti/Cu-Ni/Cu strands with Cu ratio of 0.17 and resistance of 0.91Ω/m at 10K each, showed Iq's of 7_??_7.8kArms at θ of 0° and 180° and 8.5_??_9.3kArms at θ of 90° and 270° at a bias field of 0.5Tpeak, and showed those over lOkArms at θ of 0° 90°, 180° and 270° at a bias field of 0.2Tpeak or under, both at a frequency of 51.41Hz. Though the former cable from NbTi/Cu-Ni type strands shows lower stability due to the absence of Cu, it satisfies Iq, requirement for S/N type fault current limiter of 8kArms or over at its level fields of 0.2Tpeak or less. Cables from 360 and 432 pieces of strands showed AC loses of 8_??_10kW/m3 at 0.5Tpeak, and those less than 1.8kW/m3 at 0.2Tpeak, both at 51.41Hz.
A non-inductive coil built from a 34m long 72-strand cable was operated in a 210V class experimental circuit assembled for generating short circuit current. The non-inductive coil has successfully limited 4kApeak short circuit current (or, fault current interruted) to about lOOArms within about 10ms. Thus, the availability of the cables from NbTi/Cu-Ni base strands for fault current limiter has been assured.
