Instantaneous stator power as a medium for the signature analysis of induction motors

Preventive maintenance of electric drive systems with induction motors involves continuous monitoring of operation, to detect electrical and mechanical conditions that may lead to a failure. Intensive research efforts have, for some time, been focused on motor current signature analysis (MCSA). MCSA techniques utilize results of spectral analysis of the stator current of an induction motor to diagnose abnormal conditions both in the motor and driven system. Reliable interpretation of the current spectra is difficult, as distortions of the current waveform caused by abnormalities in the drive system are usually minute. In this paper, an alternate medium for motor signature analysis, namely the instantaneous stator power, is proposed. It is shown, both by computer simulations and laboratory experiments, that the instantaneous power carries more information than the current itself, since not only the current magnitude but also the phase shift between the current and voltage waveforms are affected by irregularities in the motor or other parts of the drive system. Utilization of the instantaneous stator power as a medium for signature analysis opens new possibilities in the automated diagnosis of induction motor drives.