Electromechanical modeling of a railway induction drive prone to cage vibration failures

This paper studies the cage torsional vibrations in a traction drive comprising a variable-frequency voltage-source inverter and a fabricated-cage induction motor. End-ring vibrations may arise due to harmonic torques, with exciting frequencies matching the cage mechanical resonance frequency. It is shown that abnormal cage torsions may lead to bar breakage due to high-cycle fatigue. An actual case-study is presented, with cage vibration measurements. The measurements are matched with dynamic simulations of the complete electro-mechanical system comprising a vibrating-cage motor and the static converter. This paper shows full details of the dynamic model. Modal frequency calculation is also carried out. The model may help to identify the origin of vibrations and the fault root-cause in faulted drives, or may support the designer in preventing harmful cage resonances at the drive design stage.