Effect of rotor eccentricity in large synchronous machines

Abstract

This paper addresses the effects of rotor eccentricity on the unbalanced magnetic pull (UMP) and induced electromotive forces (EMFs) in permanent magnet and wound field machines with particular emphasis on wind applications. It is shown that in both machines, the UMP can be of similar or greater magnitude than the gravitational force acting on the rotor. It is also shown that although rotor eccentricity may have a noticeable effect on the induced EMF in individual coils, albeit the effects on the phase EMF may depend on the coil connections. Furthermore, the mechanical deflections and forces on the bearings are determined using Euler-Bernoulli beam theory taking into account the UMP and gravitational forces as well as the non-linear stiffness characteristics of the bearings. It is shown that the UMP could have a significant effect on bearing forces.