Detection of Induction Motor Broken Bar Fault Through Envelope Analysis Using Start-Up Current

AbstractThis paper has developed a technique for extraction of Low frequency oscillations below 50 hz from start-up motor current transient for detection of broken rotor fault in induction motor through envelope analysis based on instantaneous frequency defined as phase variability. The instantaneous frequency is introduced here as sinusoidal or periodic frequency is quite ineffective in tracking the fast changing frequency and amplitude during start-up motor transient. Envelope is the argument of the analytic signal obtained from complexing the start-up motor current as the real part and its Hilbert transform as the imaginary part. As the envelope works on narrow band frequencies or mono-component signal, it was analyzed using higher order wavelet at higher wavelet level which belongs to the narrow band harmonics / frequency components. In this method, the traditional difficulties in complete masking of the small amplitude harmonics or frequency components close to fundamental during FFT or problems of selecting mother wavelet(not a known priori) for transient analysis based on periodic frequencies have been overcome. Detail coefficients at higher wavelet level below 50 hz are processed to determine Power Detail Density, defined as PDD and Power Detail Energy, defined as PDE for faulty and healthy motor. PDD and PDE have been used here as fault parameters.The method works with higher detectabiliy and higher resolution. It requires less computational time,less processing power for which it can be utilized simultaneously online as well as offline. The method has been validated in a laboratory prototype