Effects of unbalanced magnetic pull in large permanent magnet machines

In addition to the circumferential shear stresses which produce torque, radial attractive stresses between the rotor and stator also exist. Although, the forces between the rotor and stator are normally negligible when they are concentric, an unbalanced magnetic pull (UMP) occurs when the rotor axis is displaced from the stator axis. In the paper, the magnitude of UMP in large permanent magnet machines and its effects on bearing forces/life are investigated. It is shown that UMP can have a significant effect on bearing life.