EET

Energy Efficiency in Action

Rings curtail bearing current in variable-frequency drive cement plant motor

A cement plant's 300-hp VFD-controlled cooler-vent fan motor uses special protection rings to safely channel harmful electrical currents away from the motor bearings to ground. This prevents a scaring of the motor bearings which otherwise would require periodic replacement.

The Aegis iPRO Bearing Protection Ring, manufactured by Electro Static Technology Inc. (EST), extends the life of the motor, installed at Monarch Cement Co. in Humboldt, Kans. The fan motor uses an iPRO split-ring model, which is designed to facilitate field retrofits. The mating halves of each iPRO install around the motor shaft without the need to decouple the motor.

If not diverted, shaft voltages can discharge through bearings, pitting the balls and race walls. In the absence of bearing protection, concentrated pitting at regular intervals along a race wall can cause washboard-like ridges called fluting, a source of noise and vibration. The eventual result is motor failure.

The bearing rings are alternatives to other products designed to protect bearings, such as conventional spring-loaded grounding brushes, which themselves require extensive maintenance. Other preventative measures, such as insulation and ceramic bearings, can shift damage to connected equipment.

To boost the electron-transfer rate, the iPRO's entire inner circumference is lined with multiple rows of conductive microfibers. These microfibers provide millions of discharge points for shaft currents and effectively divert them away from bearings to ground. Because it prolongs the life of bearings, motors, and motor-driven systems, the iPRO qualifies as sustainable technology under the Federal Energy Management Program.

Resources

Electro Static Technology Inc., www.est-aegis.com

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