Generation of Mechanical Frequency Related Harmonics in the Stray Flux Spectra of Induction Motors Suffering from Rotor Electrical Faults

Lately, the monitoring and analysis of the induction motor stray flux has been a modern trend and significant research work was accomplished. Most papers have focused on the monitoring of rotor electrical faults around the fundamental stray flux signature, imitating in this way the traditional motor current signature analysis (MCSA). However, such signatures may still have some disadvantages leading to false alarms. This is the motivation behind the use of alternative signatures, such as in this particular case and the mechanical frequency. The existence of the mechanical frequency in the stator current is still the best signature for detection of the mixed rotor eccentricity fault and load imbalances. Even healthy motors present this harmonic due to some low-level inherent eccentricity and inherent load oscillations. Despite that, it will be shown for the first time in this article that the mechanical frequency associated harmonics in the stray flux is possible to originate purely from rotor electrical faults. Those signatures present significant sensitivity to the broken bar fault severity. Moreover, they are advantageous for low load operation compared to traditional signatures. Finally, the sidebands of the mechanical frequency related harmonics are very sensitive to the broken rotor bar fault while quite immune to the number of the rotor bars.