Fault Detection Analysis in Induction Motors by Injecting Additional Test Signal

Condition monitoring methods for the dynamic performance analysis of electrical drives received considerable attention in recent years. Many of these methods use vibration sensors based on proximity probes. However, it has been suggested that stator current monitoring can provide the same indications without requiring access to the motor. Motor current signature analysis (MCSA) is now going to be a widely used method for identifying faults in induction motors. MCSA utilizes results of spectral analysis of the stator current to spot an existing or incipient failure of the motor or the drive system. Motor faults such as broken rotor bars, bearings damage and eccentricities of the rotor axis can be detected. However, when the motor is working at both low speed and low torque some problems appear, due to the small amplitude and the proximity between the frequencies to be detected. This paper proposes to inject to the machine an additional voltage test at a different frequency to the fundamental one, and then to study the resulting harmonics around the new frequencies appearing due to the composition between injected and main frequencies. Theoretical development and experimental results are presented to support the research