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Dynamic rotor faults of induction machines as broken bars and rotor eccentricity cause dynamic changes in the rotor electromagnetic field and therefore also in magnetomotive force. These changes in the electromagnetic field cause motor current amplitude and phase modulation. The rotating electromagnetic field has not a stable angular frequency but oscillates around its angular frequency. The phase demodulation of the stator current can reveal the irregularities in magnetomotive force. The phase demodulation based on the complex analytical signal enables the sensorless determination of instantaneous electromagnetic field phase angle and instantaneous angular speed and can serve as a general tool for an irregularity revolution analysis or as a diagnostic tool for rotor faults.