Variable frequency drives that control AC and DC motors induce harmful electrical voltages on the corresponding electric motor shaft. Once these voltages exceed the resistance of the bearing lubricant, they discharge through the motor’s bearings causing fusion craters, severe pitting, fluting damage, excessive bearing noise and eventually bearing failure. Damaging voltages that are induced on the shafts of AC and DC electric motors controlled by variable frequency drives are called VFD induced shaft voltages. The consistent switching of speeds in an electric motor via the variable frequency drive is generated by the insulated gate bipolar transistors and induces damaging voltages onto the electric motor shaft through parasitic capacitor coupling. This occurs between the electric motors stator and rotor.

This common mode shaft voltage seeks a path to ground through the motor’s bearings. 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. Any motor controlled by a variable frequency drive (VFD) requires bearing protection. Motors of 100 hp down to fractional hp motors will experience bearing failures when operated on a PWM drive. AEGIS® SGR Bearing Protection Ring guarantees that bearings will not fail in these motors from fluting damage for the service life of the motor.

AEGIS® SGR Bearing Protection Ring current handling capability: AEGIS® SGR is rated to discharge high frequency current. Variable frequency drives (VFD) induce high frequency EDM currents of up to 2 amps in 50 billionths of a second. AEGIS® SGR protects the bearing by safely channeling the energy away from the motor bearings to ground.
AEGIS® Bearing Protection Ring – the most reliable bearing protection: Production up-time and reliability improve when AEGIS® SGR is installed. The patented ring of hundreds of thousands of conductive micro fibers provide
protection for the service life of the motor. The fibers will always surround the shaft with a conductive path for destructive shaft currents while the motor is running. Vertical Motors: Insulate top bearing or shaft with non conductive coating. For bottom bearing, coat shaft with Colloidal Silver Shaft Coating and install AEGIS® Bearing Protection Ring.