Diagnosis of rotor broken bar in induction machines under time-varying condition

The diagnosis of rotor broken bars in induction machines (IMs) is commonly carried out by means of Motor Current Signature Analysis, i.e., by classical spectrum analysis of the input currents. Specifically in case of broken bars, the amplitude of the left and right sideband components of a phase current is monitored in order to sense their signature. However Motor Current Signature Analysis, based on Fourier Analysis, has some drawbacks that are still under investigation. The main concern is that an efficient frequency transformation cannot be made under speed-varying condition, since slip and speed vary and so does the left and right sideband frequency components. In this paper, an advanced use of the Discrete Wavelet Transform is proposed to extract the contribution of the most relevant rotor fault components, under time-varying condition with high accuracy. Experimental results show the validity of the developed approach, leading to an effective diagnosis method for broken bars in IMs operating under non-stationary conditions.