Development of a 3φ-66/6.9 kV-2 MVA REBCO superconducting transformer

Masataka Iwakuma, Kizen Sakaki, Akira Tomioka, Takeji Miyayama, Masayuki Konno, Hidemi Hayashi, Hiroshi Okamoto, Yoshihiro Gosho, Tohru Eguchi, Sigeru Yoshida, Yoshiaki Suzuki, Hirokazu Hirai, Yasuhiro Iijima, Takashi Saitoh, Teruo Izumi, Yuh Shiohara

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56 Citations (Scopus)


We have designed and fabricated a 3φ-66 kV/6.9 kV-2 MVA transformer with RE1Ba2Cu3O7-δ(REBCO, RE:Rare Earth, Y, Gd etc.) superconducting tapes. It is a 1/10 model of a 3φ-66 kV/6.9 kV-20 MVA one for a distribution power grid. The superconducting windings were reduced only in current capacity by reducing the number of tapes in parallel conductors. In the primary side, a single REBCO tape with a width of 5 mm was cylindrically wound into 8 layers. In the secondary one, an 8-strand parallel conductor was wound similarly into 2 layers, where each strand was transposed 15 times per one layer. The REBCO tapes for the secondary winding were also scribed by laser into a 3-filament structure to reduce the ac loss. The windings for 3 phases were installed into a GFRP cryostat which had an elliptic-cylinder-shape and three cylindroid bore for an iron core at room-temperature. A Ne turbo-Brayton refrigerator with a cooling capacity of 2 kW at 65 K was developed and located close to the transformer. The windings were cooled with subcooled liquid nitrogen at 65 to 70 K, which was forced-flowed by a pump unit between the transformer and the refrigerator. The completed transformer was first tested in liquid nitrogen at 77 K according to the domestic regulation for conventional transformers. The load loss, i.e., ac loss of the windings, was 26.9 W for the rated operation. The dielectric strength was also verified by applying 350 kV impulse voltage and 140 kV ac voltage for 1 minute.

Original languageEnglish
Article number6935085
JournalIEEE Transactions on Applied Superconductivity
Issue number3
Publication statusPublished - Jun 1 2015

All Science Journal Classification (ASJC) codes

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


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