Torque Oscillations of Synchronous Motors Under Starting Conditions

Salient-pole synchronous motors develop an average torque and a twice-slip frequency oscillating torque during starting. If coupled to a complex mechanical system, with resonance in the oscillatory frequency range, severe stresses may result in shafts, gears, and couplings. The objective of the paper is to develop motor and mechanical system models, which can lead to the analysis of the torsional response of the motor load, and to avoid the use of specific motors that yield excessive values of stress or take steps to mitigate the oscillation magnitudes. The effect of the field discharge resistance was investigated.