Rotor bars breakage in railway traction squirrel cage induction motors and diagnosis by MCSA technique Part I : Accurate fault simulations and spectral analyses

In this paper the rotor bar fault diagnosis problem for a particular induction motor (1.13 MW) employed in high speed-railway traction is considered, by getting realistic simulations of the electromechanical converter behaviour in specified working and feeding conditions. The use of a complete motor phase model and the implementation of the real GTO-inverter waveforms (three-pulses PWM modulation) allow accurate computation of the machine currents (both stator and rotor currents), and of the real mechanical internal stresses. The numerous data needed for model settings were obtained by F.E.M. and identification of the inductance parameters was performed starting from few measured values and some informations about internal machine structure. Some simulations are shown, and matched with measured waveforms. Bar breakages are easily recognized as produced by PWM-generated harmonic torques. The simulated stator phase currents are then analyzed by FFT in healthy and faulty rotor conditions. Finally, all the fault-related harmonic current components (sidebands) are found, and diagnostic criteria are evaluated and discussed. In a companion paper theoretical formulations were developed for frequency and amplitude sidebands prediction and calculation.