Superconducting-electromagnetic hybrid bearing using YBCO bulk blocks for passive axial levitation

A superconducting/electromagnetic hybrid bearing has been designed using ac tive radial electromagnetic positioning and a superconducting passive axial levitator. This bearing has been tested for an induction machine with a ve rtical shaft. The prototype was conceived as a four-pole, two-phase inducti on machine using specially designed stater windings for delivering torque a nd radial positioning simultaneously. The radial bearing uses four eddy-cur rent sensors, displaced 90 degrees from each other, for measuring the shaft position and a PID control system for feeding back the currents. The state r windings have been adapted from the ones of a standard induction motor. T he superconducting axial bearing has been assembled with commercial NdFeB p ermanent magnets and a set of seven top-seeded-melt-textured YBCO large-gra in cylindrical blocks. The bearing set-up was previously simulated by a fin ite element method for different permanent magnet-superconductor block conf igurations. The stiffness of the superconducting axial bearing has been inv estigated by measuring by a dynamic method the vertical and transversal ela stic constants for different field cooling processes. The resulting elastic constants show a Linear dependence on the air gap, i.e, the clearance betw een the permanent magnet assembly and the set of superconducting large-grai n blocks, which is dependent on cooling distance.