Study of shaft voltage & bearing currents in electrical machines

Shaft voltage & bearing currents in electric motors are not new. Its presence is noticed probably after the invention of electric rotating machines which is confirmed by observing pitting in the bearing rubbing surfaces and changing the chemical composition of lubricating oil or grease used in the bearings. Currents flowing through motor bearings have the potential of creating premature failure of bearings. This paper discusses about the origination of shaft voltage and bearing currents. A few mitigation techniques are also touched upon.