Equal current distribution in parallel circuits of resistive superconducting fault current limiters using multiple superconducting inter-phase transformers

Differences in impedances of the superconducting parallel circuits during normal operations cause unequal distribution of currents in the circuits, resulting in quench or loss in certain superconducting parts. However, those impedances are so small that they are hardly controllable. To solve this problem, attempted were such measures as inserting resistors or inductors into each of the parallel circuits in series. This leaves extra losses due to resistance or reactance. In this study, we proposed a multiple superconducting inter-phase-transformers (SIPT) for the equal current distribution in superconducting parallel circuits and investigated their performance. SIPTs were fabricated using double pancake windings of BSCCO-2223 HTS tapes and were applied to parallel circuits of resistive superconducting fault current limiters (SFCLs). Results showed that the SIPTs effectively made the current distribution uniform in superconducting parallel circuits that had unequal resistances. In addition, the secondary loop configuration with air-core SIPTs was suggested as the most efficient for the SFCLs.