Low-cost inverter based detection of rotor faults in induction machines for quality management systems

Most fault detection systems for rotor bar defects require specific load conditions or at least sufficient moments of inertia to establish a minimum load by repetitive acceleration or deceleration. The application of a method able to detect a rotor defect at no load condition is thus advantageous especially for quality management systems in the manufacturing process where a high number of machines have to be tested with minimum consumption of electrical power an without coupling the machines using a test rig or additional moment of inertia. The method proposed in this paper is based on a modulation of the machines rotor flux magnitude in different directions of the rotor and a determination of the magnetizing/demagnetizing time constant It thus does not depend on any kind of load. For high power machines this offers the additional benefit of a reduced inverter power rating in the quality management line as only the magnetizing current of the machine has to be supplied. Moreover the method may be applied in safety critical applications for maintenance purposes, even in line-fed drives. Simulations as well as measurement results will be presented to show the applicability of the method.