Induction Motor Shaft-Frame Voltage Analysis

Most three-phase, squirrel-cage, induction motor (SCIM) fault diagnosis/detection techniques are based on the analysis of the stator currents and/or frame mechanical vibration. In this paper, a preliminary theoretical and experimental analysis of the shaft-frame voltage (SFV) in line-fed SCIMs, as a potential fault diagnosis and/or condition monitoring technique, is presented. Since SFV waveform analysis requires the acquisition of only one very-low-amplitude shaft-frame voltage through a rotating shaft electrical contact brush, its practical implementation in industrial facilities is inexpensive, easy, and safe. In SCIMs, faults associated with stator-rotor electromagnetic asymmetries or bearing defects will change the amplitude of specific SFV harmonic components and produce disturbances in the SFV waveform, and therefore can be effectively detected through a proper SFV analysis (SFVA) in the frequency and time domains. The experimental tests performed on a 4-kW SCIM under different supply voltage and load conditions, stator winding connection modes, and stator winding interturn short-circuits, show that SFVA can potentially be used for detecting faults in bearings and stator windings, as well for identifying abnormal supply voltage conditions and stator winding connection mode. Hence, SFVA could be applied in industrial SCIMs as a complementary technique for industrial SCIM condition monitoring. Yet, further studies are required to establish clear SFV criteria in the frequency and time domains associated with most common fault modes in SCIMs.