Oscillatory Torques During Synchronous Motor Starting

A fundamental characteristic of the salient-pole synchronous motor is a twice-slip frequency torque pulsation during acceleration. Although frequently neglected, sound application engineering requires an understanding of this subject. The way twice-slip frequency torques are produced in synchronous machines is discussed, as are the effects of these torques on mechanical system considerations such as critical speeds and stress buildup in shafts. Finally, specific areas of design coordination between designers of electrical power systems, synchronous motors, and the mechanical components of the system are suggested.