AC over-current test results of YBCO conductor for YBCO power transformer with fault current limiting function

• Published in: Physica. C, Superconductivity Superconductivity, 2011-11, Vol.471 (21-22), p.1367-1373
• Main Authors: Tomioka, A., Otonari, T., Ogata, T., Iwakuma, M., Okamoto, H., Hayashi, H., Iijima, Y., Saito, T., Gosho, Y., Tanabe, K., Izumi, T., Shiohara, Y.
• Format: Article
• Language: English
• Subjects: AC over-current; Alternating current; Conductors (devices); Constraining; COPPER OXIDE; ELECTRICAL CONDUCTORS; Fault current limiting; MATHEMATICAL ANALYSIS; Mathematical models; Superconducting tapes; Superconducting transformer; SUPERCONDUCTIVITY; SUPERCONDUCTORS; TAPE; Transformers; YBCO; YBCO superconductors; YTTRIUM OXIDE
• ISSN: 0921-4534; 1873-2143
• DOI: 10.1016/j.physc.2011.05.196

► The single-layer coils with a diameter of 250mm and 12 turns were manufactured with YBCO tapes with a CuNi- or Cu-Tape. ► The AC over-current tests were carried out in subcooled liquid nitrogen at 66K and 74K to develop power transformers with current limiting function. ► The AC over-current was two to seven times larger than the Ic of conductor and it was reduced to the same level of Ic. ► The Ic of model coils did not degrade. ► The test results showed the possibility of YBCO superconducting transformers with current limiting function. We are developing elemental technology for 66kV/6.9kV 20 MVA-class YBCO power transformer. The YBCO transformer is considered to have a possibility to stabilize the power system by improving function of fault current limiting. Current limiting behavior functions over critical current flows. There is a possibility that superconducting characteristic may be damaged due to increase in temperature of YBCO tapes. Therefore, we have taken a measure to combine YBCO tape with CuNi tape or Cu Tape. We manufactured model coils using these conductors and conducted the AC over-current tests. The test current was two to seven times larger than the Ic of conductor and it was damped with time from its maximum value according to the generation of conductor resistance. We verified the effectiveness of current limiting characteristics. In these tests, the Ic of model coil did not degrade. We consider this conductor to be able to withstand AC over-current with the function of current limiting.