Electrical bearing damage — A lurking problem in inverter-driven traction motors

Abstract

With the increasing use of inverter-controlled traction motor systems in electric rail, road, and off-road vehicles, protecting motor bearings will become a key requirement for reliability. Partial mitigation measures against inverter-induced electrical bearing damage can merely shift the damage to gearbox bearings and create more maintenance headaches. In some vehicles, stray currents can also cause electromagnetic interference (EMI) and/or radio frequency interference (RFI) that can jeopardize electronic control systems. The best long-term solution is a contact/noncontact motor shaft grounding ring that works in the unique electric vehicle environment of high revolutions per minute (r/min), rapid acceleration, etc.