Fabrication and evaluation of superconducting magnetic bearing for 10 kW h-class flywheel energy storage system

Radial-type superconducting magnetic bearings (SMB) have been developed for a 10 kW h-class flywheel energy storage system. The bearings consist of an inner-cylindrical stator composed of YBCO bulk superconductors and an outer-rotor composed of permanent magnets. The rotor is suspended without contact using the pinning forces of the bulk superconductors. After construction of the whole system, various tests on both static and dynamic characteristics of the SMB were carried out to confirm that the SMB has sufficient performance for 10 kW h-class flywheel systems. Besides, the bearing rotation loss was measured. In this paper, we describe the implementation of the stator part and report the SMB test results, namely that the rotor was successfully suspended up to 7500 rpm. Thus we succeeded in the energy storage of 2.24 kW h. The rotation loss of the SMB was estimated as 40 W at 7500 rpm, which was mainly caused by the inhomogeneous magnetic field of the bulk superconductors.