Diagnosis of rotor fault in induction motor using the MUSIC analysis of the terminal voltage after switch-off

This paper presents a spectrum analysis of the terminal voltage after supply disconnection. This voltage is induced only by the rotor flux and does not depend on the mechanical load, the voltage supply time harmonics, etc... The diagnosis technique is based on monitoring the amplitude of harmonics components in the frequency domain using both FFT and MUSIC methods. The experimental results show the presence of harmonics of order 6mplusmn1, m=1,2,3... for healthy and faulty machine. When there is a rotor bar fault, the amplitude of these harmonics grows. The spectral analysis shows that MUSIC method is more reliable than the FFT technique, and the induced voltage technique is independent on the load level.