Rotational Power Loss on a Rotor Radially Supported by Electrodynamic Passive Magnetic Bearings

Homopolar radial electrodynamic bearings (EDBs) are one type of passive magnetic bearing that exploits eddy currents developing in a rotating conductor to produce levitation forces. When the rotor spins at high speed and an external force causes the axis of rotation to move radially with respect to the symmetry axis of the static magnetic field, the relative motion between the two members causes currents to be induced in the rotor which in turn generate a reaction force. Since the currents are induced inside the rotor, the rotational loss is converted into heat in the rotating member. Because EDBs are especially suitable for applications that run continuously and that usually work in vacuum, e.g., flywheels and turbomolecular pumps, an evaluation of the bearing’s losses in working conditions is of extreme importance. The present paper investigates the amount of rotational loss that is produced by an EDB in working conditions. The analysis is performed using an electromechanical model of the EDB coupled to a Jeffcott rotor model. The analysis allows deducing a set of design equations that can be used to predict the bearing’s losses during the design phase. The model is validated by comparison with finite element model.