TY - JOUR

T1 - Theoretical Analysis of Additional AC Loss Properties of Two-Strand Transposed Parallel Conductors Composed of REBCO Superconducting Tapes

AU - Oki, Soichiro

AU - Miura, Shun

AU - Iwakuma, Masataka

N1 - Publisher Copyright:
© 2018 IEEE.

PY - 2018/4

Y1 - 2018/4

N2 - Superconducting tapes made of REBa2Cu3Oy (REBCO; RE: rare earth, i.e., Y, Gd, or Eu) exhibit superior performance at the critical current density, even at liquid-nitrogen temperatures. However, the current capacity of these tapes must be enhanced for use in large-scale applications. We have proposed a method of constructing parallel conductors, which must be insulated and transposed to obtain uniform current sharing and low ac loss. If the transposition points deviate from the optimal ones, a shielding current is induced to maintain a constant interlinkage magnetic flux, which produces an additional ac loss. In our previous studies, the theoretical expressions for the additional ac loss were derived on the basis of a critical state model. In this study, by using an n-value model to express the I-V characteristics of REBCO superconducting tapes, we theoretically investigated the additional ac loss properties of two-strand transposed parallel conductors wound into solenoid coils. The results showed that under the nonsaturation condition, the additional ac loss increases with decreasing n value. This suggests that in parallel conductors composed of REBCO tapes that operate at liquid-nitrogen temperatures, transposition must be performed with high accuracy at the optimal points. To avoid increasing the additional ac loss, the n value of the tapes must be consistently larger than approximately 10, and the deviation of the transposition point should remain below a few percent of the conductor length.

AB - Superconducting tapes made of REBa2Cu3Oy (REBCO; RE: rare earth, i.e., Y, Gd, or Eu) exhibit superior performance at the critical current density, even at liquid-nitrogen temperatures. However, the current capacity of these tapes must be enhanced for use in large-scale applications. We have proposed a method of constructing parallel conductors, which must be insulated and transposed to obtain uniform current sharing and low ac loss. If the transposition points deviate from the optimal ones, a shielding current is induced to maintain a constant interlinkage magnetic flux, which produces an additional ac loss. In our previous studies, the theoretical expressions for the additional ac loss were derived on the basis of a critical state model. In this study, by using an n-value model to express the I-V characteristics of REBCO superconducting tapes, we theoretically investigated the additional ac loss properties of two-strand transposed parallel conductors wound into solenoid coils. The results showed that under the nonsaturation condition, the additional ac loss increases with decreasing n value. This suggests that in parallel conductors composed of REBCO tapes that operate at liquid-nitrogen temperatures, transposition must be performed with high accuracy at the optimal points. To avoid increasing the additional ac loss, the n value of the tapes must be consistently larger than approximately 10, and the deviation of the transposition point should remain below a few percent of the conductor length.

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U2 - 10.1109/TASC.2018.2794978

DO - 10.1109/TASC.2018.2794978

M3 - Article

AN - SCOPUS:85040939567

SN - 1051-8223

VL - 28

JO - IEEE Transactions on Applied Superconductivity

JF - IEEE Transactions on Applied Superconductivity

IS - 3

M1 - 8263126

ER -