Calculation of unbalanced magnetic pull in a salient-pole synchronous generator

The unbalanced magnetic forces which act upon the rotor of a salient-pole synchronous generator due to eccentric motion of the rotor shaft in the presence of magnetic field originating from the field current in no-load operation have been calculated using finite-element method. The displacement of the rotor has been modeled using the actual shaft orbit recorded on a 5 MVA salient-pole generator driven by a gas turbine in a cogeneration plant. The results indicate that a variation of unbalanced forces in no-load operation at rated voltage occurs at the precession frequency of 25 Hz with maximum force of 2.32 kN.