Torque Oscillations of Synchronous Motors Under Starting Conditions.

Salient pole synchronous motors develop an average torque and an oscillatory torque at twice slip frequency during starting. If coupled to a complex mechanical system, with resonances in the oscillatory torque frequency range, severe stresses may result in shafts, gearing and coupling. The objective of this research was to develop motor and mechanical system models which can be computerized to analyze the torsional response of a motor with given parameters on a specific, previously designed, mechanical system, and if necessary, avoid the use of motors that yield excessive values of stress as to take steps to mitigate the oscillation magnitudes. In addition to the development of models and algorithms to calculate performance and predict possible failure, such as deformation of components during starting, the effect of the magnitude of external field resistance, during starting, on peak oscillatory torque magnitudes, slip ring voltages, average torque, and the slip at which maximum torque occurs is as investigated. It was found that the value of external field resistance used had a marked effect on these quantities.