Premature Wear and Recurring Bearing Failures in an Inverter-Driven Induction Motor—Part II: The Proposed Solution

In a previous work, a real case of recurring bearing failures in an induction motor had been extensively studied. As a result, the cause of the problem was revealed to be the circulation of electric current through the bearings. In this way, the present paper deals with the high-frequency leakage currents in ac motors fed by pulsewidth-modulation inverters, contextualized in the analysis of an actual case. From the parameters of an equivalent circuit representing the connecting cable, motor, and inverter return path, a filter, characterized by a common-mode transformer, is designed to mitigate the common-mode quantities and the correlated problems. Both simulated and experimental results show that the proposed solution represents an advantageous alternative in comparison to the traditional $RC$ and $RLC$ filters, since, in addition to its effect on the common-mode quantities, it dissipates a negligible amount of power.