Abstract: A formula for calculation of bending and torsional electromagnetic stiffness was derived from the
expression of magnetic field energy in the hydro generator rotor air gap. A bending and torsional coupled
vibration model was developed for the hydroelectric generating set rotor-bearing system with consideration
of these stiffnesses. This model was used to examine the coupling effect of the two stiffnesses on
bending-torsional coupled vibrations in different conditions of journal bearing support and to study the
influence of centralized bearing damping on the features of coupled vibrations. The results show that the two
electromagnetic stiffnesses produce an effect of coupled excitation and amplification on the amplitudes of
bending and torsional vibrations. The stiffness and centralized damping of journal bearing have important
effects on the coupled vibrations, though a slight difference appears between the effects on bending vibration
and torsional vibration.