Papers by Keyword: AC Loss

Abstract: This paper presents our recent activities for the development of low-loss (Bi,Pb)-2223 tapes with interfilamentary resistive barriers. To suppress the side effect on the phase formation in the filaments during sintering, SrZrO3 were selected as barrier materials. Moreover, small amount of Bi-2212 was mixed with SrZrO3 to improve their ductility for cold working. For non-twisted barrier tapes, transport critical current densities Jc at 77 K and self-field were ranged between 18 and 21 kA/cm2 and its uniformity within 4% along a 1 m length. By combining the barrier introduction, reducing the tape width (< 3 mm) and twisting the filaments tightly, coupling frequency fc exceeded 250 Hz even in an AC perpendicular field at 77 K. Transport Jc of the barrier tapes with tightly twisted filaments were in the range of 1214 kA/cm2 at 77 K and self-field. In our knowledge, this is the first result to achieve both Jc > 12 kA/cm2 and fc > 250 Hz simultaneously in an isolated (Bi,Pb)-2223 tape. At 50 mT and 50 Hz, our twisted barrier tapes showed 60-70% lower perpendicular field losses than a conventional 4 mm-width tape with fully coupled filaments.

Abstract: Ag-sheathed Bi2223 composite tapes with interfilamentary resistive barriers were successfully fabricated by using a powder-in-tube (PIT) method and their AC loss properties at 77 K are evaluated. The mixture of Ca2CuO3 and 30 wt% Bi2212 was used as the barrier material for tape fabrication to make an electromagnetic decoupling between the filaments. The barrier layers formed on all surfaces of hexagonal monocore wires by a dip-coating method, and several pieces of the coated wires were stacked and inserted into an Ag tube. Subsequently, the composites deformed into tape shape and subjected to a standard process consisting of a flat rolling and sintering. Degradations in the Jc values at 77 K and self-field by introducing the barriers were estimated to be at most 15%. The transverse resistivity and AC loss properties under AC external magnetic fields for the barrier tapes were examined and compared with those for the tape without barriers. The results showed that an introduction of Ca2CuO3 barriers was effective to suppress the electromagnetic coupling among the filaments and also to reduce the magnetization losses under parallel transverse field. The fabrication of the barrier tapes on the order of several meters, together with the uniformity of superconducting properties along a length direction has been also presented.

Abstract: Having undertaken studies into a lightweight and highly efficient superconducting transformer for rolling stock, we developed a prototype with a primary winding, four secondary windings and a tertiary winding using Bi-2223 high temperature superconducting wire. Its primary voltage is 25kV, which is widely adopted as the catenary voltage on the world's high-speed lines. We adopted liquid nitrogen cooling, the weight being 1.71t excluding the refrigerator. The maximum output available to maintain superconductivity is 3.5MVA. We also introduce railways in Japan.

Abstract: We fabricated Ag-sheathed Bi2223 composite tapes with interfilamentary resistive barriers by using powder-in-tube (PIT) method and evaluated their AC loss characteristics at 77 K. The mixture of Ca2CuO3 and 30 wt% Bi2212 are used as the barrier material for tape fabrication. The barrier layers were coated on all surfaces of the hexagonal monocore wires. Then, several pieces of the coated wires were stacked and inserted into an Ag tube, and the composites were deformed into tape shape. By introducing the barrier layers between the filaments, the Jc values at 77 K and self-field are degraded about 15%. The loss measurements under AC parallel transverse magnetic field were systematically performed, as a function of field amplitude and frequency. The loss properties in the barrier tape were compared with those in the tape without barriers. The results indicated that introducing Ca2CuO3 barriers is effective to suppress the electromagnetic coupling among the filaments and also to reduce the magnetization losses under parallel transverse field. We also present the fabrication of the barrier tapes on the order of several meters, together with the uniformity of superconducting properties along a length direction.