Broken-bar Fault Detection by Injecting a Frequency Modulated Continuous Wave Signal

It is challenging to detect broken-bar faults in squirrel-cage induction motors using motor current signature analysis (MCSA) due to the small magnitude and proximity of the fault signature relative to the operating frequency component, especially when the motor slip is very small. In this paper we propose a signal injection method to detect the broken-bar fault by injecting a frequency modulated continuous wave (FMCW) signal to the stator voltage. Model analysis and simulation show that under broken-bar fault conditions, the injected FMCW signal induces another FMCW signal of a lower frequency band, which as a newly-defined fault signature can be extracted by analyzing cross correlation between the injected signal and the induced signal in the frequency domain. Compared to other signal injection methods, our method is more robust and insusceptible to harmonic interference. Experimental results on a three-phase squirrel-cage induction motor validate our method in detecting broken-bar faults from noisy measurements even when the motor slip is very small.