Development of a REBCO superconducting transformer with current limiting function

A single-phase 10 kVA transformer was designed and fabricated with RE ₁Ba₂Cu₃0O_7-6 (REBCO, RE: Rare Earth) superconducting tapes to quantitatively investigate the transition phenomenon of REBCO superconducting tapes to normal state due to a fault excess current. The voltage ratio was 1:1 and the rated voltage was 393 V. It had four windings. The primary and secondary windings had auxiliary windings in addition to main ones respectively. The main and auxiliary windings were connected in parallel in the both sides. The addition of the auxiliary windings made it possible to observe the induced normal resistances in the respective main ones individually. First usual performance tests were carried out and a stable operation as designed was confirmed. In steady state almost all of the current flowed in the main windings due to the small leakage reactance between them. At a sudden short-circuit test, the main windings quenched due to excess current over the critical current and the current was reduced to one fortieth as compared with the case of no current limiting function. It was clarified the whole of the main windings did not shift to normal state though the current exceeded the critical current all over the length and the induced normal zone was almost proportional to the primary voltage.