Bi2223 multifilamentary tapes with enhanced transverse resistivity by introducing Ca2CuO3 and SrZrO3 as interfilamentary barriers were prepared and their AC loss properties were examined under AC external magnetic field. To improve the deformation properties of these oxide powders, 20-30wt% Bi2212 powders were mixed with them. The mixed oxide powders were introduced among the twisted Bi2223 filaments by using dip-coating method. AC loss properties under AC parallel or perpendicular field were measured and compared with the results for the tape without barriers. The loss measurements were carried out by changing both the amplitude and the frequency of external field. Based on the experimental results, the effect of barrier introduction on the loss reductions was discussed.
AC loss reduction in Bi-2223 tapes is one of the key issues for the realization of power cables and transformers. The large loss generation is mainly attributed to the strong electromagnetic coupling between the filaments in AC external magnetic field. In this paper, we fabricated twisted Bi-2223 tapes with interfilamentary oxide barrier and evaluate their AC loss properties. To suppress the side effect on Bi-2223 phase formation during sintering, Ca 2 CuO 3 or SrZrO 3 powders were used as barrier materials.Furthermore, small amounts of Bi-2212 powders were mixed with them to improve their ductility for cold working. AC loss characteristics were examined at 77 K in parallel and perpendicular transverse magnetic fields with various field amplitudes and frequencies.The effect of introducing different oxide barriers on AC loss reduction at different operating condition is discussed.
Synopsis: Bi2223 multifilamentary tapes with interfilamentary oxide barriers were fabricated and their AC loss properties were examined under AC external magnetic field. In order to avoid the side effect on Bi2223 phase formation during heat treatment, Ca 2 CuO 3 and SrZrO 3 with average grain sizes of 1-2 μm were selected as barrier materials. Furthermore, an additional Bi2212 powder corresponding to 20wt% were mixed with them to improve their deformation properties for cold working. The mixed oxide powders were introduced among the twisted Bi2223 filaments. The critical current densities (J c ) in the barrier tapes were 10-20% lower than those in the tapes without barriers. In a parallel field, the loss reduction in the SrZrO 3 /Bi2212 barrier tape is most remarkable because the continuity of the SrZrO 3 /Bi2212 barriers is far superior to the Ca 2 CuO 3 /Bi2212 barriers. At 50 mT around power-grid frequencies, parallel field losses in a twisted tape with SrZrO 3 /Bi2212 barriers are 80% lower than the nontwisted tape. From the frequency dependence of AC losses in a perpendicular field, it was confirmed that the transverse resistivity in the SrZrO 3 /Bi2212 barrier tape is 8-9 times higher than the tape without barriers. However, around the power-grid frequencies, the introduction of barrier reduces AC losses only slightly in a perpendicular field. The twist pitch of the present barrier tape (= 16 mm) is probably too long to decouple the filaments in a perpendicular field.
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