The most common reason for a low-voltage induction motor breakdown is a bearingfailure. Along with the increasing popularity of modern frequency converters, bearingfailures have become the most important motor fault type. Conditions in which bearingcurrents are likely to occur are generated as a side effect of fast du/dt switchingtransients. Once present, different types of bearing currents can accelerate themechanical wear of bearings by causing deformation of metal parts in the bearing anddegradation of the lubricating oil properties.The bearing current phenomena are wellknown, and several bearing current measurement and mitigation methods have beenproposed. Nevertheless, in order to develop more feasible methods to measure andmitigate bearing currents, better knowledge of the phenomena is required. Whenmechanical wear is caused by bearing currents, the resulting aging impact has to bemonitored and dealt with. Moreover, because of the stepwise aging mechanism,periodically executed condition monitoring measurements have been found ineffective.Thus, there is a need for feasible bearing current measurement methods that can beapplied in parallel with the normal operation of series production drive systems. Inorder to reach the objectives of feasibility and applicability, nonintrusive measurementmethods are preferred.In this doctoral dissertation, the characteristics and conditions of bearings that arerelated to the occurrence of different kinds of bearing currents are studied. Further, thestudy introduces some nonintrusive radio-frequency-signal-based approaches to detectand measure parameters that are associated with the accelerated bearing wear caused bybearing currents.
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