High Speed Asynchronous Motor with Tc Superconducting Magnetic Bearings

The discovery of High Tc Superconductors has renewed the interest for practical applications of superconductivity including devices based on magnetic levitation. To evaluate their potential use for near-frictionless high speed passive magnetic bearings, a prototype of an asynchronous motor with the rotor floating on two melt textured YBs^ Cuj 07.x suitably shaped blocks has been built and tested. The low radial stiffness of the bearings compels one to use non-conventional motor configurations, in order to avoid radial instability under load. In the present paper the design of the electric motor and the experimental testing of the superconducting bearings, in terms of levitation force versus rotor height and magnetic stiffness, are described. The characterization of the bearings allows one to perform a rotor-dynamics study of the whole machine, whose results are then validated experimentally. The bearing drag is evaluated through spin-down tests.