Abstract:

Fault detection based on a common steady-state analysis technique, such as FFT, is known to be significantly dependant on the loading conditions of induction motors. At light load, it is difficult to distinguish between healthy and faulty rotors because the characteristic broken rotor bar fault frequencies are very close to the fundamental component and their amplitudes are small in comparison. As a result, detection of the fault and classification of the fault severity under light load is almost impossible. In order to overcome this problem, this paper investigates the detection of rotor faults in induction machines by analysing the starting current using a newly developed quantification technique based on the wavelet transform. The analysis technique applies the wavelet transform to the envelope of the starting current. The envelope extraction is used to remove the strong fundamental component, which overshadows the characteristic differences between a healthy motor and a faulty motor with broken rotor bars. The results are then verified using tests on a machine with a varying numbers of broken bars. The effects of initial rotor position, supply imbalance and loading are also investigated.