Calculation of Unbalanced Magnetic Pull in a Salient-Pole Synchronous Generator Using Finite-Element Method and Measured Shaft Orbit

In this paper, 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 in no-load and loaded condition are calculated using the finite-element method. The displacement of the rotor is modeled using the actual shaft orbit measured on a 5-MVA salient-pole generator driven by a gas turbine in a cogeneration plant. The influences of the stator winding parallel paths and the rotor damper winding on attenuation of unbalanced magnetic pull are analyzed using the finite-element method. It is shown that under linear conditions the correlations between separate harmonic components of the shaft orbit, the resulting harmonic components of the unbalanced magnetic pull and the induced stator winding currents can be established in both the no-load and loaded condition.