Gear up your bearings

This article identified three electrical mechanisms that cause bearing damage. The three sources of bearing currents are electromagnetic induction (circulating current), electrostatic EDM coupled sources (mechanical or electrical coupled), and ground sources (backfeeding). This also presented field test measurements related to bearing damage. A field methodology was presented to identify electrical bearing conditions in motors that are still running. Mitigation actions are described and applied to two motor ASD application sites. Test measurements were taken to determine the effectiveness of the mitigation action. In most cases, two or all of the bearing current mechanisms can be identified by reviewing the installation and application of the motor with voltage and current measurements with time and frequency analysis. A combination of mitigation strategies is normally used on the basis of the bearing current coupling mechanisms.