Variable frequency drives (VFDs) enable precise speed control and significant energy savings, but they can also cause motor bearing failure. VFDs take smooth electric power and break it up into pulses. These pulses create a voltage imbalance in the motor that can build up on the shaft. This shaft voltage can discharge through the bearings, causing cumulative damage and premature motor failure.

These destructive discharges can be seen with a digital oscilloscope equipped with a conductive microfiber probe tip, like the AEGIS® Shaft Voltage Tester™. A typical bearing discharge is shown on the left below, where voltage gradually builds up to several volts (~20V here) and then suddenly collapses back to baseline.

meter readings

Shaft voltages on a motor before (left) and after (right) installation of an AEGIS® Shaft Grounding Ring. The voltage scale is the same in both images.

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FlowServe Bearing Gard isolators with AEGIS ® grounding ring technologySpecially designed for VFD-driven motors in harsh washdown and processing environments, Flowserve’s new Bearing Gard™ bearing isolator protects against both contaminant ingress and VFD-induced electrical bearing damage. The isolator’s unique design offers both static and dynamic protection against contamination ingress. A unique double drive ring design, an innovative static labyrinth shut-off, and an oversized contamination channel provide superior protection against harmful contaminants. And Bearing Gard’s built-in AEGIS® Bearing Protection Ring channels VFD-induced shaft voltages away from motor bearings and safely to ground.

Bearing Gard™ Bearing Isolators are available from stock in standard and slimline versions for motors with shaft diameters of 0.875 – 6.000 inches (23 – 152mm). Custom sizes are also available.

For more information on Bearing Gard™ Isolators with AEGIS® Bearing Protection, click here.