Sequences of field-oriented control for the detection of faulty rotor bars in induction machines-the Vienna Monitoring Method

Rotor cage asymmetries of induction machines cause disturbances of the air-gap flux pattern. These deviations affect torque and speed as well as stator terminal voltages and currents. The proposed fault detection technique senses the actual machine state with the help of real-time space-phasor models. The Vienna Monitoring Method compares online a voltage model output with a current model and observes the deviations in a rotor fixed reference frame. High accuracy and robustness allow the detection of a faulty rotor bar out of the switched voltage and current signals of an inverter-fed machine in an early state. The focus of this paper is the detection of a single rotor bar increase under transient speed conditions without the necessity of a clutched load. During an inverter-controlled acceleration, lasting only 200 ms, the Vienna Monitoring Method evaluates currents, voltages, and rotor position for the calculation of an indication quantity that allows for reliable detection. As only one acceleration task does not excite every rotor cage bar sufficiently, a set of acceleration and deceleration cycles has to be driven.