Converter-fed induction motor diagnosis using instantaneous electromagnetic torque and power signals

This paper deals with the problem of the early stator (the short-circuits) and rotor (broken bars) faults detection of the induction motors supplied from the frequency converter. The method basing on the FFT algorithm is used for the spectral analysis of the instantaneous active power, the instantaneous reactive power and the estimated electromagnetic torque. These signals are on-line calculated, basing on the measured currents and voltages of the motor. Computations of the instantaneous active and reactive power use the theory of the electric power for non-sinusoidal power systems. In this paper results of laboratory investigations for low power motor with modeled stator short-circuit and broken rotor bars are demonstrated. Tests were realized for different supply frequencies, what enabled the evaluating of the usefulness of the proposed analysis in the diagnostics of the stator and rotor faults in the converter-fed induction motor drives.