An Overview of Shaft Voltages and Bearing Currents in Rotating Machines

Shaft voltages and associated “shaft currents” or “bearing currents” have been known since more than a century on DC and AC motors under classical line operation. More recently with the emergence of inverter drives, there has been an increase of high-frequencies bearing currents and shaft voltages creating mainly premature failure of bearings. Although those phenomena and the associated mitigation techniques are now well-known, one must be kept in mind that there are still potential issues for industrials. Lots of papers have analyzed these concerns and proposed various models and remedies. The purpose of this article is to give an overview on the subject, from causes and origins of shaft voltages, mitigation techniques for engineers new to this subject, to measurements methods, fault diagnosis and online condition monitoring. Finally it is believed that condition monitoring and fault diagnosis through shafts will expend from generators to Induction Motors and Permanent Magnet Synchronous Motors.