A high speed (30,000 rpm) superconducting motor / generator demonstrator is currently being built at Robinson Research Institute. This will enable applications such as flywheel energy storage systems, direct-drive generators, and high speed microfans to be explored whilst also providing the opportunity to demonstrate key technology elements such as flux-pumped REBCO field windings and low-loss high speed bearings. The focus of this paper is to explore the development of suitable low-loss bearings from bulk REBCO superconductors.
The heat generated by conventional bearings limits the maximum design speed of any motor. If they can be reliably designed, then REBCO / permanent magnet (PM) bearings offer the potential for simplified, low-loss maglev bearings that would operate at high speed and loads. These bearings are contactless and appear low loss, but the AC loss mainly caused by magnetic field inhomogeneity has not been fully explored. Therefore, AC loss is a key parameter when designing and evaluating HTS bearings.
Spin-down tests, where the speed decay of the spinning PM structure is measured over time, allows this AC loss to be measured accurately. It is challenging to engineer a reliable spin-up, release, and recapture mechanism that will work with a levitating spinning PM. In this paper we will show the design, build, and evaluation of an experimental test rig that we have proven experimentally at up to 22,000 rpm. In this paper, we will discuss key aspects of the rig including the special self-aligning PM holder and evaluation with different PM sizes. This will be used as a key tool to measure AC loss due to inhomogeneity and allow motor bearing designs evaluation.

Keywords: High speed superconducting motor, Maglev bearings, AC loss, Spin down test