Fundamental study on high Tc superconducting magnetic bearings for flywheel system

Basic quasi-static tests of superconducting magnetic bearings are carried out using YBa/sub 2/Cu/sub 3/O/sub 7-/spl alpha// (YBCO) and Nd-Fe-B permanent magnets. In the thrust type tests, two kinds of c-axis oriented YBCO bulks are used. These YBCO bulks are produced by a melt process using a seed crystal. The measured maximum repulsion pressure between the YBCO and the magnet between the YBCO and the magnet is 0.14 MPa at 77 K under the zero-magnetic-field cooling condition. This repulsion pressure, which is a top level value, enables the authors to consider the application of the superconducting magnetic bearings. The attractive forces between the YBCO and the magnet under the field cooling condition are also measured at 77 K. In the radial type tests, the force between a ring-shaped YBCO bulk and a shaft combined with multi-ring magnets are measured in the liquid nitrogen. A simplified formula is proposed to evaluate the repulsion force. As an application of the superconducting magnetic bearings, a flywheel system is preliminary designed for the energy storage of one kilowatt-hour. The flywheel, which is made of fiber reinforced plastic, is a ring shape having an outer diameter of 600 mm and a height of 100 mm.<>