The analysis of induction motor electromagnetic field and shaft revolution oscillations at dynamic rotor faults

Dynamic rotor faults of induction machines as broken bars or rotor dynamic eccentricity cause dynamic changes in the rotor electromagnetic field and therefore also in the magnetomotive force. These changes cause motor current amplitude and phase modulation. The phase modulation causes that the rotating electromagnetic field has not a stable angular frequency but oscillates around its angular frequency. The phase demodulation enables the sensorless determination of rotating electromagnetic field phase angle oscillations. The oscillation of rotating electromagnetic field transfers depending on motor load and inertia to the motor shaft revolution oscillation which may adversely affect motor operation. The paper solves this problematic by the simultaneous analysis of both oscillations at various motor working conditions.