Investigation of the physical mechanisms in rolling bearings during the passage of electric current

With the increasing use of frequency converters as control units for electric motors, bearing failures caused by the passage of electric current through the bearings are more common. This paper discusses the most relevant parasitic current loops in frequency converter-driven motors that can lead to damage of bearing raceways or deterioration of lubricants. Electrical stray capacitances, which are inevitably present in any electric motor, in combination with the high-frequency components of the drive voltages, have been identified as the source of electric discharge machining (EDM) currents. Based on an EDM equivalent electric circuit, the passage of electric current through the rolling contact of a bearing is simulated. A set-up is introduced to initiate EDM processes in bearings under well-controlled electrical and mechanical conditions. The effect of EDM currents on bearing elements in the presence of different lubricants is studied. Initial results are presented.