Induction Drives Diagnosis by Signal Injection: Effectiveness and Severity Classification

The "signal injection technique" introduced to realize speed sensorless induction drive exploiting rotor asymmetry effects, is an attractive procedure for diagnostic purposes as well. At first it was proposed as alternative technique to detect rotor damage, then its use has been extended to stator short circuit detection. An important issue is the possibility to state the fault severity, linking the amplitude of the novel spectral components 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 bar breakage diagnosis and stator short circuit detection is investigated and compared with the classical MCSA procedures. Simple machine models are presented that allow to state relationships between the fault entity and the amplitude of specific spectrum lines in stator current or current space vector. Experiments and theoretical analysis show that for broken bars this technique has some advantages with respect to MCSA. On the contrary in case of stator short circuits the signal injection techniques is not suitable for diagnostic purposes, being the specific line amplitude only partially affected by the fault