Case Study: Electrical Bearing Damage in a Water Treatment Plant

In 2009, the city of Hutchinson, Kansas opened its new Reverse Osmosis Water Treatment Center.  The plant uses 17 pump motors, all controlled by variable frequency drives, to move water through the treatment process and to the city's supply towers.

The Hutchinson Reverse Osmosis Water Treatment Center
But just two months after the plant came online, the pump motors' bearings began to fail.  It started with a 250 hp vertical pump motor that began to squeal.  The manufacturer replaced that motor's bearings, but soon other motors developed the same problem.  Clearly, there was something wrong here!

 

Some of the many VFD-driven vertical hollow shaft motors at Hutchinson WTP

The plant turned to a new motor repair contractor, Independent Electric Machinery Company.  Independent Electric found the cause of the problem.  The drives controlling the motors were creating voltage on the shaft.  That voltage caused arcing through the bearings, producing pitting, roughening, and eventual failure.  Luckily, Independent Electric had experience with electrical bearing damage.

In fact, they had developed what they call the Vertical Motor Solution.  This consists of isolating the thrust bearing, and installing an AEGIS® Shaft Grounding Ring at the guide bearing.  The AEGIS ring bleeds voltage safely off the shaft before it can arc.  And the insulation prevents circulating currents.

In all, ten vertical pump motors had been damaged before they got the Vertical Motor Solution.  After that, AEGIS rings and bearing insulation were installed on the other seven pump motors.

 

An AEGIS Shaft Grounding Ring mounted inside the guide bearing retainer of a vertical pump motor

The bearings haven't failed since.

This ordeal made an impression on Dan Biby, an engineer who helped design the plant and dealt with this problem.  He said, "We use the rings on all of our jobs to eliminate downtime, replacement, and installation costs.  Installing rings can prevent these problems altogether.  And the cost is insignificant when compared to the total project cost."

Over the years, motor manufacturers have become aware of this problem.  Nowadays, both vertical and horizontal motors are available with AEGIS rings factory-installed.  In fact, US Motors (Nidec) has made AEGIS rings standard in their CORRO-DUTY® Vertical HOLLOSHAFT® motors.

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.

AEGIS Shaft Grounding Rings will be on display at the WEFTEC 2021 Technical Exhibition in Chicago this October 18-20th. Stop by Booth 3957 and meet the team, see a live demonstration of how AEGIS rings reduce shaft voltage and pick up a copy of the Bearing Protection Handbook. See you at the show!

This blog post is based on this case study.