On a New Type of Inverter-Induced Bearing Current in Large Drives With One Journal Bearing

We report on a new type of inverter-induced bearing current (BC) that can occur with large inverter-based drive systems with one journal bearing. This current is a variation of the high-frequency circulating BC type that has been described by different authors over the last years. As with the first, the BC mirrors the common-mode (CM) current as a result of inductive coupling. However, the voltage across the bearing also mirrors the stator winding CM 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.