The analysis of vibration signals during induction motor starting transients with a view to early fault detection

Condition monitoring is becoming an increasingly used method of determining maintenance intervals by operators of large 3-phase induction motors. Many of the existing techniques require that the motor in question be under load before reliable diagnoses can be carried out. There are certain situations where it is either impractical or undesirable to test a machine under loaded conditions. Certain machines, as a result of their operational environment, or perhaps because they have been moved to a workshop for repair cannot be tested under loaded conditions. This project describes the monitoring and analysis of stator core vibration signals during no-load starting transient on a 3-phase induction motor with specifically introduced stator-rotor eccentricity. Records of stator core vibration signals during full voltage, direct on line starting transients for various degrees of eccentricity have been captured from test rigs and these signals have been analysed in both the time and frequency domains. A range of digital signal processing techniques has been developed which indicate that slot harmonics, whose magnitudes are known to be functions of the level of eccentricity, can be monitored throughout the transient. The results have shown that it is possible to differentiate between the degree of eccentricity as a result of the analysis of a single starting transient.