Radial type superconducting magnetic bearings have been developed for a 10 kWh-class flywheel energy storage system. The bearings consist of an inner-cylindrical stator of YBCO bulk superconductors and an outer-rotor of permanent magnets. The rotor is suspended without contact via the pinning forces of the bulk superconductors that are arranged such that the -axis of each superconductor is aligned parallel to the radial direction of the cylinder. In this paper, we describe the implementation of the stator part and report the SMB test results, namely that the rotor was successfully rotated at up to 7,500 rpm. Thus we succeeded in energy storage of 2.24 kWh.Index Terms-Flywheel energy storage system, pinning force, radial type superconducting magnetic bearings, YBCO bulk superconductors.

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