Shaft voltage and bearing current - a common phenomenon in electric machines

Presence of shaft voltage & bearing currents were noticed probably after the invention of electric rotating machines. Pittings on the bearing surfaces, changes in the chemical composition of bearing lubricants and premature bearing failures were some of the evidences of these phenomena. This paper discusses about the bearing mechanism and its failure causes. Origination of shaft voltage is elaborately presented here. Types of bearing currents and its mitigation techniques are also discussed briefly.