بحث بعنوان Comparison Between Vibration and Stator Current Analysis for the Detection of Bearing Faults in Asynchronous Drives

بحث بعنوان
Comparison Between Vibration and Stator Current Analysis for the Detection of Bearing Faults in Asynchronous Drives
Baptiste Trajin, Jérémi Regnier, Jean Faucher
Abstract: 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.
Conclusions
In this paper, some methods for the detection of bearing
faults in induction motors using vibration and stator
current monitoring have been presented. On artificially
damaged bearings, a vibration spectrum analysis has been
proposed to detect and diagnose the faults. This method
has been compared to classical techniques such as scalar
indicators and advanced signal processing methods.
Mechanical considerations have shown that bearing defects
induce preferentially load torque oscillations comparing to
eccentricity. Thus, the effects of load torque oscillations on
stator current have been recalled. The amplitude variation
law of the stator current components has been determined
by experimental measurements and simulation results. The
resonance point has been used to amplify slight load torque
oscillations and to allow detecting preferentially inner or
outer race fault. An automatic detector based on stator
current spectral analysis has been presented and validated
on localised faults and naturally damaged bearing.
Comparison between vibration and stator current indicators
has been presented. Restrictions of the detector concerning its
Figure 8 Cumulative sums of relative error in % for the
detection of naturally damaged bearing
Table 3 Example of fault harmonics in vibration spectrum of
a naturally damaged bearing for fr 25 Hz
Harmonic frequency Energy variation, dB
8.8definition and the consideration of the electromechanical
behaviour of the test bench have been discussed. This has
led to indications concerning the choice of detection
methods depending on the considered system. Compared to
vibration analysis, the stator current detector needs less
expensive instrumentation. However, the vibration indicator
is usable in several applications. To extend the application of
fault detection, condition monitoring on variable speed
drives could be studied by using time-frequency or time
scale analysis to detect bearing faults at the start-up of the
machine. Moreover, other faulty conditions such as
lubricant contamination or grease wear could be investigated
on stator current along the lifetime of the bearing. Finally,
other mechanical quantities such as mechanical speed or
torque can be studied by measurements or estimation.

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