A Study about Turning Three-Phase Electrical Motors in Active Magnetic Bearings

Nowadays, the operation principle of active magnetic bearings (AMB’s) is well known and their industrialization can be considered mature. Nevertheless, spreading this technology around all the world is yet a tough work as its actual production cost is even high. Taking an operative rotational machine, by instance, in the process of a substitution of mechanical bearings by magnetic ones, as the mechanical details are customized, the stator construction cost can be quite expensive. In this sense, in order to save time and reduce costs, an alternative approach has been studied. This consists on turning conventional AC electrical motors in AMB’s. Different from a previous reported work, where a twophase induction motor was modified and experimentally tested, in this work, a three-phase induction motor is studied through Finite Elements Analysis. Its distributed windings structure is unchanged while the rotor is substituted by another one without a squirrel cage. To simulate the AMB behavior, two conditions were evaluated: first, two phase windings were supplied, while the third one was kept open, and second, all the three phase windings were supplied. Finally, the equivalent net forces were evaluated as a function of differential control currents, holding the rotor centralized, and also as a function of the radial displacements, holding all the windings currents constant. Simulation results show that supplying the three windings is desirable from the point of view of the radial displacement control.