Fault Diagnostics of AC Motor Bearings Based on Envelope Analysis of Vibration Residual Signal

Vibration-based condition monitoring of AC motor bearing is a challenging task as the vibration signal has tremendous background noise including motion from other rotating components and electromagnetic noise. This leads to vibration signals with a low signal-to-noise ratio (SNR) which makes the fault feature submerged in other signatures. To accurately monitor the bearing condition, this paper proposed an effective technique to diagnose the defect on the bearing outer race. Firstly, a newly defined threshold based on the rotating frequency of the motor rotor was proposed to calculate the residual signal of motor vibration so as to remove the effect from other characteristic frequencies. Then, the envelope analysis was performed on the residual signal to get the fault features. The results show that compared with the conventional envelope analysis of raw vibration signal, the residual signal envelope can effectively filter the non-fault related characteristic frequencies and keeps the fault frequency and its harmonics, which gives a high SNR for reliable fault diagnosis.