On a New Type of Inverter-Induced Bearing Current in Large Drives with Oil-Lubricated Bearings

We report on a new type of inverter-induced bearing current that can occur with large inverter-based drive systems with one journal bearing. This current is a variation of the "high-frequency circulating" bearing current type which has been described by different authors over the last years. As with the first, the bearing-current mirrors the common-mode current as a result of inductive coupling. However, the voltage across the bearing also mirrors the stator winding common- mode voltage and is not reduced to zero by the current flow. We show experimental results of measured currents and give physical explanations, from which we then derive an effective mitigation technique, which is also illustrated through measurement results.