Electrical Discharge
Voltage can build on the shaft until the bearing grease film is exceeded and a discharge path forms through the bearing.
TECHNICAL EDUCATION
Understanding Shaft Currents
and VFD Bearing Damage
Modern variable frequency drives can contribute to common-mode shaft voltage and electrical discharge through motor bearings.
Understanding the Damage Mechanism
Modern variable frequency drives provide valuable speed and process control, but switching activity can also contribute to
common-mode shaft voltage and electrical discharge through motor bearings.
Pitting & Frosting
Repeated microscopic discharges can mark bearing surfaces and contribute to progressive damage.
Fluting & Vibration
Continued electrical damage can develop into patterned fluting, noise, vibration and premature bearing failure.
Lubricant and Driven-Equipment Considerations
Electrical activity can affect bearing surfaces and can also contribute to lubricant oxidation and hardened grease. The broader motor system must therefore be considered, including driven equipment, insulated bearings, insulated bearing housings and the selected shaft-grounding method.
Why a Controlled Grounding Path Matters
Earthrings are intended to provide a controlled low-impedance path from the shaft to the grounded motor frame, reducing the tendency for the bearing to become the discharge path.
Explore the Technical Resources
Review product, installation and bearing-protection documents from the original Earthrings websites.