Rotor torsional resonance detection in induction drives by MCSA focused on rotor slot harmonics

Torsional resonances may incur in induction drives due to large harmonic torques produced by the inverter. The torsion can affect the rotor-load system, but more sneaky resonances may arise in the rotor end-rings of fabricated-cage induction motors. Abnormal cage torsions may lead to bar breakage due to high-cycle fatigue. Since the high-frequency speed oscillations are difficult to detect, torsional resonances may go unnoticed and lead to drive fault on the long run. This paper proposes a non-invasive technique for early detection of high-frequency speed fluctuations in case of mechanical resonance, by using motor current signature analysis. The rotor slot harmonics (usually researched for rotor eccentricity detection or for drive speed estimation) are originally used here to detect drive speed fluctuations. Simulations of the motor-converter system carried out by winding function approach show the feasibility of this kind of motor condition monitoring.