The short-circuit test results of 6.9 kV/2.3 kV 400 kVA-class YBCO model transformer with fault current limiting function

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We are developing an elemental technology for 66/6.9kV 20MVA-class superconducting power transformer with fault current limiting function. In order to obtain the characteristics of YBCO conductor when the AC over current supplied to the conductor, the model coils were manufactured with YBCO tapes and tested. Based on these results, we manufactured the 6.9kV/2.3kV 400kVA-class YBCO model transformer with fault current limiting function and performed short-circuit test. At the 0.25s after short-circuit, the short-circuit current of primary winding was limited to about 174A for a prospective current of 559A. It was consistent with the design. The I–V characteristics of the winding did not change before and after the test. We consider the model transformer to be able to withstand AC over-current with the function of current limiting. The results suggest the possibility to design YBCO superconducting transformers with fault current limiting function for practical power grid.