Pulsed Field Magnetization Properties of Bulk RE-Ba-Cu-O as Pole-Field Magnets for HTS Rotating Machines

Aiming at exploiting the high trapped field ability of bulk high-temperature RE-Ba-Cu-O (RE: rare-earth elements) superconductors, a brushless axial-gap type superconducting synchronous motor has been successfully developed as a technology demonstrator using eight melt-textured GdBa₂Cu₃O_y (Gd-123) bulks as pole-field magnets. An output power of 10 kW at 720 rpm was realized by an average trapped field peak of 0.56 T reaching the armature coils, under a pulsed field excitation at the liquid nitrogen temperature. For such motors, to improve the trapped flux of bulks is a direct way to enhance the motor performance. In order to obtain a high trapped flux density with a regular shape for a high performance motor utilization, the pulsed field magnetization (PFM) properties of two kinds of bulk superconductors have been investigated. By a reasonable multi-PFM process with a pair of vortex-type pulsed coils, it was found that the multi-seed Y-Ba-Cu-O bulk can bring a high average trapped field, while the single-grain Gd-Ba-Cu-O bulk under a size-adjustable pulsed coil can obtain a very regular trapped field distribution. These results will be useful to the following optimization of the rotating machine system.