Influence of load torque on the detection of rotor faults by means of the sensorless Vienna monitoring method

The Vienna monitoring method (VMM) is a model based rotor fault detection technique for squirrel cage induction machines. It compares the torques calculated by a voltage and a current model, respectively. The voltage model evaluates the voltage and the current space phasor, whereas the current model processes the current space phasor ill the rotor fixed frame. The transformation from the stator into rotor fixed reference frame is performed with the help of the instantaneous rotor position. For the conventional VMM rotor position has been measured. The sensorless approach presented in this contribution estimates the rotor angle. This demanded signal is extracted from the double slip frequency modulation of the shaft torque, which is caused by a rotor fault. The presented scheme is a reliable and load independent rotor fault detection scheme without, position sensor. Fault specific load torque modulations, even with a severe rotor fault, vanish for slightly loaded induction machines. This is a physical phenomenon, which causes that the rotor position signal may not be tracked if the machine is unloaded. The practical aspects of the influence of load torque on the presented sensorless VMM are investigated in this paper.