Comparison between vibration and stator current analysis for the detection of bearing faults in asynchronous drives

This study deals with the application of vibration and motor current spectral analysis for the monitoring of rolling bearings damage in asynchronous drives. Vibration measurement is widely used to detect faulty bearings operations. However, this approach is expensive and cannot always be performed, while electrical quantities such as the machine stator current are often already measured for control and detection purposes. Signal processing methods and global indicators associated with bearing fault detection of vibration measurements are recalled. Compared to these methods, an automatic detector based on vibration spectral energy extraction is then proposed and its performances are discussed. Moreover, load torque measurements underlines that bearing faults also induce mechanical load torque oscillations. Therefore a theoretical stator current model in case of load torque oscillations is used to demonstrate the presence of phase modulation (PM) on stator currents. Frequency behaviour of the related sideband components is strongly investigated for monitoring purposes. Thus, a fault detector using the extraction of spectral energy of stator current is proposed to detect damaged bearings. This detector is then compared to the one defined on vibration signals.