The Use of Higher-Order Spectrum for Fault Quantification of Industrial Electric Motors

This chapter proposes a new method of electric motor fault quantification. Higher Order Spectrum (HOS) is a signal processing used as a fault quantification technique. Previous researches have shown that the faults in the stator or rotor generally show sideband frequencies around the main frequency (50 Hz) and its higher harmonics in the spectrum of the Motor Current Signature Analysis (MCSA). However in the present experimental studies such observations are not seen, but the faults in the stator or the rotor may distort the sinusoidal response of the motor RPM and the main frequency. Hence this research proposes the HOS here, namely the Bispectrum of the MCSA, because it relates to both amplitude and phase of number of harmonics in a signal. The Bispectrum with the unwrapped phase angle along its frequency is also analyzed. The tests can show that the proposed method can detect the faults accurately. The proposed method can also show that the severity level of the faults can be measured by observing the change in the heights of the Bispectrum amplitude.