Operation of induction machines with electromagnetic irregularities

The paper presents application data showing an induction motor developing torque at zero slip. This condition can prevent proper field commissioning of the motor drive system and contribute to inferior system performance. The paper examines rotor asymmetries, one cause for the nonzero torque condition. Voltage and current spectra, for current regulated and volts per hertz controllers, are presented. Another source for the nonzero torque at zero slip, machine space harmonics, is discussed and analyzed. The paper examines contributions to abnormal machine operation of each source by examining the signals present in the respective waveforms. Control strategies are developed where appropriate to mitigate the adverse effects of the motor irregularities.