Induction Drives Diagnosis by Signal Injection: Effectiveness and Severity Classification

The “signal injection technique” introduced torealize speed sensorless induction drive exploiting rotorasymmetry effects, is an attractive procedure for diagnosticpurposes as well. At first it was proposed as alternative techniqueto detect rotor damage, then its use has been extended to statorshort circuit detection. An important issue is the possibility tostate the fault severity, linking the amplitude of the novel spectralcomponents induced by the injected signal to the fault entity,avoiding the dumping action of the regulator.In this paper the signal injection technique for rotor barbreakage diagnosis and stator short circuit detection isinvestigated and compared with the classical MCSA procedures.Simple machine models are presented that allow to staterelationships between the fault entity and the amplitude ofspecific spectrum lines in stator current or current space vector.Experiments and theoretical analysis show that for brokenbars this technique has some advantages with respect to MCSA.On the contrary in case of stator short circuits the signalinjection techniques is not suitable for diagnostic purposes, beingthe specific line amplitude only partially affected by the fault.