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 PWM inverters, contextualized in the analysis of an actual case. From the parameters of an equivalent circuit in terms of cables, motor and inverter return path, a filter, characterized by a common-mode transformer, is proposed to mitigate the common-mode quantities and the correlated problem. 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.