Abstract
Fault size estimation is of great importance to bearing performance degradation assessment and life prediction. Until now, fault size estimation has generally been based on acoustic emission signals or vibration signals; an approach based on current signals has not yet been mentioned. In the present research, an approximate estimation approach based on current is introduced. The proposed approach is easy to implement for existing inverter-driven induction motors without complicated calculations and additional sensors, immune to external disturbances, and suitable for harsh conditions. Firstly, a feature transmission route from spall, to Hertzian forces, and then to friction torque is simulated based on a spall model and dynamic model of the bearing. Based on simulated results, the relation between spall size and the multiple characteristic vibration frequencies in friction torque is revealed. Secondly, the multiple characteristic vibration frequencies modulated in the current is investigated. Analysis results show that those frequencies modulated in the current are independent of each other, without spectrum overlap. Thirdly, to address the issue of which fault features modulated in the current are very weak, a fault-feature-highlighting approach based on reduced voltage frequency ratio is proposed. Finally, experimental tests were conducted. The obtained results validate that the proposed approach is feasible and effective for spall size estimation.
Highlights
Induction motors play an important role in many industrial and on-board applications because of their low cost, simple construction, and high reliability
For tracking multiple characteristic vibration frequencies modulated in current, the squared method alone is far from enough; this paper attempts to improve the signal-to-noise ratio (SNR) based on envelope of current based on Hilbert transform is employed to suppress noise
This paper proposes an approximate fault size estimation approach based on current, which is immune to external environmental interference, addressing the shortcomings of existing approaches which are not suitable for applications in some special and harsh environments
Summary
Induction motors play an important role in many industrial and on-board applications because of their low cost, simple construction, and high reliability. A novel idea which tracks the two events in the frequency domain is proposed in the present work To address this issue, the feature transmission route from spall, to Hertzian forces, to friction torque, and to current, is investigated detailedly. Noise suppression in current-based bearing fault diagnosis is focused on elimination of the fundamental supply frequency and its harmonics. To address this problem, some effective approaches are proposed based on notch filters [18], the noise cancellation method using time shifting [17], and the Teager-Kaiser energy operator [16], etc. A simple and feasible spall size estimation approach by tracking multiple vibration frequencies in current is introduced.
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