Characteristics of shaft voltage and bearing currents

This article reviews investigations into reduced bearing life due to voltage source adjustable speed drive (ASD) AC motor operation. Relevant bearing failure mechanisms and indicators are discussed. dv/dt and electric discharge machining (EDM) contributions are discussed and experimental data presented showing the voltage levels on motor shafts when operating with ASDs. Finally, techniques to reduce shaft voltage are discussed, along with the electrical characteristics and interaction of system components. The example chosen is electrostatic shielded induction motors.