Detection of mechanical load faults in induction motors at variable speed using stator current time-frequency analysis

This paper examines the detection of mechanical load faults in induction motors during speed transients by stator current analysis. Mechanical load faults generally lead to load torque oscillations at specific frequencies. these frequencies are related to the mechanical rotor speed. The torque oscillations produce a characteristic sinusoidal phase modulation of the stator current. Speed transients result in time-varying supply frequencies that prevent the classical, Fourier transform based spectral estimation. This problem can be overcome using time-frequency signal analysis. The methods applied in this paper are instantaneous frequency estimation and the Wigner Distribution. Furthermore, an adaptive demodulation method is proposed. The theoretical considerations are validated on signals obtained from an experimental setup.