Pumping Systems on VFD Need Bearing Protection
In most pump applications, running the pump at full speed is not always necessary. 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. AEGIS rings can be installed on existing motors, and several manufacturers also offer motors with AEGIS rings factory-installed, including vertical hollowshaft, severe duty, and even explosion-proof models.
AEGIS Rings also 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 monthly live training webinars, and - pandemic restrictions permitting - we can also visit your facility to review your exact application.
* Image: AEGIS rings being installed on pump motors at Blue Ash Recreation Facility in Blue Ash, OH