Preliminary tests of a 500 kVA-class oxide superconducting transformer cooled by subcooled Nitrogen

K. Funaki, M. Iwakuma, M. Takeo, K. Yamafuji, J. Suehiro, M. Hara

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43 Citations (Scopus)


We have designed and fabricated a 500 kVA-class oxide superconducting power transformer operated in subcooled nitrogen. The primary and secondary windings are three- and six-strand parallel conductors of Bi-2223 Agsheathed multifilamentary tapes, respectively. In the parallel conductors, the strands are transposed several times for a uniform current distribution among them. First, the transformer cooled by liquid nitrogen of 77 K was steadily operated with a 500 kVA secondary inductive load. The efficiency in the full operation at 77 K attains to 99.1 % even with the refrigeration penalty of liquid nitrogen, 20, for the thermal load to the coolant. We installed the transformer in a continuous flow system of subcooled nitrogen as a fundamental step for compact superconducting transformers operating in subcooled nitrogen with a single-stage refrigerator. Short-circuit tests of the transformer were also performed in a region of temperature below 70 K. The transformer was operated with no quenching up to a level of critical current at 66 K, that is equivalent to 800 kVA. The efficiency estimated was improved to 99.3 % in the subcooled nitrogen.

Original languageEnglish
Pages (from-to)824-827
Number of pages4
JournalIEEE Transactions on Applied Superconductivity
Issue number2 PART 1
Publication statusPublished - 1997

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Electrical and Electronic Engineering


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