Experimental Validation of Theoretical Expressions on Additional AC Loss of Two-Strand Parallel Conductors Composed of REBa ₂ Cu ₃ O _y Tapes via Pick-Up-Coil Method

By a pick-up-coil method, the additional ac loss due to the formation of two-strand parallel conductors consisting of REBa ₂ Cu ₃ O _y (REBCO, RE = rare earth) superconducting tapes was experimentally investigated. We recently improved the theoretical expression of the additional ac loss assuming that the voltage-current characteristics are expressed by the n-value model. The objective of this study is to prove the validity of the improved theoretical expression by experiment. The two insulated REBCO strands were cowound into a one-layer solenoidal coil. A uniform external magnetic field was applied in the axial direction of the sample coil. The additional ac losses were measured by the pick-up-coil method in sinusoidal ac magnetic fields whose maximum amplitude and frequency are 0.1 T and 10 Hz, respectively. The observed additional ac losses corresponded with the theoretical prediction. Therefore, it was concluded that the improved theoretical expression is more accurate than the previous one. At high-frequency regions, the observed additional ac losses slightly deviated from the theoretical predictions.