AC losses of HTS tapes and bundles with de-coupling barriers

Plastronic Inc. is working on a project for the Ballistic Missile Defense O rganization to improve the strength and ac loss characteristics of Bi-based High Temperature Superconductors (HTS) for ac applications like motors, ge nerators, and transmission cables. High strength, high amperage conductor i s made by encapsulating bundles of HTS tapes with a non-silver sheath. With this technique, Cu-alloy spacers can be placed between Bi-2223/Ag HTS tape s to decouple the tapes under ac currents. AC losses were measured on condu ctor bundles with and without Cu-alloy spacers at ac currents up to 70 A an d frequencies from 50 to 400 Hz. At frequencies up to about 100 Hg it was f ound that the bundle with resistive barriers had ac loss equal to the sum o f individual tapes as expected from the Norris ellipse model. At higher fre quencies, the Cu-alloy barrier was not as effective in reducing the ac loss . For single tapes, Zr-oxide was used to coat the HTS filaments before stac king to form a multifilament tape. AC loss measurements of 6-filament tapes with and without the oxide coating showed little effect of the coating whe n the loss was normalized to the square of the critical current as the theo ry suggests.