Pumping Systems on VFD Need Bearing Protection


                      AEGIS rings being installed on pump motors at Blue Ash Recreation Facility in Blue Ash, OH

In most pump applications, it is not always necessary to run the pump at full speed.  Flow rate has traditionally been decreased with flow control valves, but this has disadvantages.  Nowadays the flow is often controlled by running the pump’s motor on a variable frequency drive (VFD). Besides well-controlled flow rates, VFDs offer:

  • Energy savings (from reduced motor speeds)
  • Improved seal and impeller life and reduced vibration and noise (from reduced pressure)
  • Greatly reduced water hammer (from smooth acceleration and deceleration)

But VFDs have their own downsides. One big problem is that they create stray voltage on the motor shaft. This shaft voltage can cause electrical damage to motor and pump bearings by discharging (arcing) through them. This electrical damage accrues over time, causing premature bearing failure.

The solution is to electrically bond the shaft to the motor frame with a shaft grounding device. This gives charge on the shaft a low-resistance path to ground, so current flows through the grounding device instead of arcing through the bearings.  (Large motors, over 100 hp/75 kW also require one insulated bearing to prevent circulating VFD-induced currents.)

AEGIS® Shaft Grounding Rings are the most reliable form of shaft grounding available, and the only one that offers a 2-year extended warranty.  AEGIS rings can be installed on existing motors, and several manufacturers also offer motors with AEGIS rings factory-installed, including vertical hollowshaftsevere duty, and even explosion proof models.

To learn more about the problem of VFD-induced bearing currents and the solution using AEGIS rings, see these case studies and best practices, or see the AEGIS Youtube channel.

As mentioned, AEGIS Rings come with a 2-year extended warranty against bearing fluting damage. No other form of protection against VFD-caused bearing damage offers a warranty like this.

To learn more about AEGIS shaft grounding and best practices for electrical bearing protection, sign up for a training. We offer both live webinars and on-site lunch-and-learn trainings.