A New Approach for Induction Motor Broken Bar Diagnosis by Using Vibration Spectrum

Different methods for detecting broken bars in induction motors can be found in literature. Many of these methods are based on evaluating special frequency magnitudes in machine signals spectrums. Current, power, flux, etc are among these signals. Frequencies related to broken rotor fault are dependent on slip; therefore, correct diagnosis of fault depends on accurate determination of motor velocity and slip. The traditional methods typically require several sensors that should be pre-installed in some cases. A practical diagnosis method should be easily performed in site and does not take too much time. This paper presents a diagnosing method based on only a vibration sensor. Motor velocity oscillation due to broken rotor causes frequency components at twice slip frequency difference around speed frequency in vibration spectrum. Speed frequency and its harmonics as well as twice supply frequency, can easily and accurately be found in vibration spectrum, therefore the motor slip can be computed. Now components related to rotor fault can be found. According to this method, an apparatus consisting necessary hardware and software has been designed. Experimental tests have confirmed the efficiency of the method