Study of inverter-induced bearing damage monitoring in variable-speed-driven motor systems

Abstract

Bearing currents are parasitic phenomenon which is commonly present inmodern inverterdriven motors. At this date the root causes of this phenomenon can be considered as well identified - mainly occurring due to magnetic flux unbalance and high-frequency components of the common-mode voltage. However, the mitigation techniques, that were developed to reduce the negative effect of this phenomenon on the life time of motors, are not yet at the level, where the problem could be resolved with a standardized method. That is mainly due to the prevalence of various bearing current subtypes in different motor size groups and types, and due to the limited ways to retrofit the machinery, that is already in the exploitation.

This work presents the review of state-of-art in diagnostic methods and insight on the physical processes, that occur in presence of bearing currents and cause deterioration of motor life time. The work further reviews and combines the results of the recent research, that focuses on the aspects of diagnosing defects, caused by bearing current using the vibration and radio-frequency based methods. After that, the work presents analytical model, that is aimed as a way to develop new methods of diagnosing the defects, caused by bearing currents. Finally, the model is used to evaluate the vibration analysis techniques, that are commonly used nowadays and to establish their sensitivity to some of the parameters of motor operation.