Electromagnetic Axial Bearing With Reduced Thrust-Disc Diameter for High-Speed Machines

Electromagnetic axial bearings (EABs) are preferred over conventional thrust bearings for their contactless and lubrication-free operation, besides longer life in supporting the rotor of an electrical machine against axial forces. An EAB exerts a magnetic force on a thrust disc, attached normally to the shaft, countering the axial forces on the rotor. For large axial forces, the thrust disc should also have a large area, which can adversely affect the mechanical stresses, rotordynamics, and maximum operating speed. This article aims to arrive at a modified EAB geometry, along with a systematic design procedure, to reduce the thrust disc diameter significantly for a given load capacity. First, an improved design procedure is proposed for the conventional geometry EAB, which maximizes force density per unit MMF. A modified geometry and the proposed design procedure are then utilized to achieve an EAB of a given load capacity, but with a significant reduction in the thrust-disc diameter. Laboratory prototypes of both geometries are fabricated and are compared theoretically and experimentally. The modified geometry is shown to achieve a comparable load capacity as that of the conventional geometry, with the thrust-disc diameter reduced by 30%, along with about 50% reduction in peak material stress.