Progress of superconducting bearing technologies for flywheel energy storage systems

Abstract Recent advances on superconducting magnetic bearing (SMB) technologies for flywheel energies storage systems (FESSs) are reviewed based on the results of NEDO flywheel project (2000–2004). We constructed a radial-type SMB model for 100 kW h class FESSs and evaluated the bearing characteristics. The SMB model consists of a superconducting stator of YBCO bulks and a NdFeB permanent magnet circuit. The levitation force density reached 11 N/cm 2 at 77 K, and the time decay of levitation force was suppressed in allowable ranges by adopting such techniques as “pre-loading” or “super-cooling” method. The rotation loss was reduced by means of improving the homogeneity of magnetic field distribution in both permanent magnet circuit and superconducting bulk stator. The availability of radial-type SMB for FESS was investigated by constructing 10 kW h class FESS using both SMB and active magnetic bearings. The operation test resulted in the energy storage of 5.0 kW h at rotation speed of 11,250 rpm. A further reduction of rotation losses is a crucial issue for its wide range of applications.