Differential Diagnosis Based on Multivariable Monitoring to Assess Induction Machine Rotor Conditions

Multi-variable supervision systems for on-line monitoring of induction motors allow large versatility and diagnosis robustness. As regards rotor faults, the diagnostic procedure based on sideband current components may fail due to the presence of inter-bar currents that reduce the degree of rotor asymmetry and, thus, the amplitude of these spectral components. On the other hand, the inter-bar currents produce core vibrations in the axial direction; these vibrations can be detected using a suitable vibration sensor. In this paper a differential fault analysis based on traditional MCSA and on radial and axial vibration monitoring is proposed to discern cases in which the presence of inter-bar currents decreases the sensitivity of MCSA. The features of stator currents and of radial and axial core vibration signals are investigated in order to increase the reliability of the diagnostic system. Moreover, to explore the possibility of obtaining further information, stray flux signals are taken into account.