Bearings and energy storage

The discovery of the new high temperature superconductors and especially the discovery of YBCO in 1988 has led to a great deal of interest in the use of superconductors as an active component in noncontact magnetic bearings. A conventional magnetic bearing cannot be composed of entirely passive components. Arrangements of permanent magnets may be stable in up to five out of six axes (three translational, three rotational) but there will always be instability in at least one axis. By replacing one or more of the magnets by a section of bulk superconductor, a bearing can be constructed which is stable in all six axes. Thus, a so-called passive magnetic bearing may be constructed. Such a bearing, however, has limitations as it has very low stiffness and is vulnerable to large excursions (or changes in loading) under the influence of which the equilibrium position or the bearing gap may change. Here, the author describes how it is therefore ideally suited to applications such as flywheels for energy storage in which dynamic loads are small and where there is a requirement for a simple low-maintenance bearing with minimal power requirements.