Electrical Discharge Machining (EDM) occurs when currents arc through the dielectric oil film between the rolling elements and the bearing race. This causes fusion craters, severe pitting, and eventually bearing fluting (a washboard-like pattern in the bearing race) which results in premature bearing failure.
High Frequency Circulating Currents in Large AC and DC Motors: In addition to potential bearing failures in motors from VFD induced EDM currents, AC and DC motors above 100 hp (75 kW) may also experience bearing failures caused by high frequency circulating currents. VFD induced high frequency circulating currents are in the kilohertz or even megahertz range and circulate through the motor’s bearings because of magnetic flux imbalances in the stator. This type of VFD induced current becomes the more dominant destructive current in higher hp/kW motors.
COLLOIDIAL SILVER SHAFT COATING
Improving the conductivity of the steel shaft surface enhances the shaft voltage discharge capability in AEGIS® shaft grounding applications. Maintaining a highly conductive shaft surface is especially important in critical applications or in applications where the conductive shaft surface of steel could become compromised. Environmental elements could create a potential for decreased conductivity on the shaft of the motor.
Apply AEGIS® CS015 Colloidal Silver Shaft Coating to any VFD driven motor shaft prior to installing AEGIS® Bearing Protection Ring.
25 hp motor -
AEGIS® installed on drive end