In 2016, a midwestern American university had a problem. Their HVAC motors running on variable frequency drives (VFDs) had serious bearing problems. First, the affected motors would make a loud high-pitched noise. Then the bearings would fail entirely. As repair costs mounted, their Facilities Department requested Engineering to investigate.
During their investigation, Engineering used an electrical discharge detector and found moderate to severe electrical discharge in every motor on a VFD. Worse, discharge was also found in the pumps coupled to these motors. Motor repair or replacement gets expensive, but pumps are typically more expensive than the motors that drive them.
Rather than assuming that the VFDs were to blame, Engineering first looked into the repair logs. Did motors on drives need more repairs than motors run on line power? Indeed they did. In fact, almost no repairs had been made to pumps or motors that were not equipped with VFDs. The evidence was clear: VFDs were causing the damage.
This raised the question: If drives cause so much damage, are they even worth using? The answer is yes. In the three buildings surveyed, the university spent an average of $14,000 per year on repairs. But in those same buildings, the drives gave annual energy savings of over $63,000. Deducting repair costs, the average savings was still $49,000.
But the engineers knew they could do better. So they recommended 
requiring electrical bearing protection for all motors on VFDs. This would include AEGIS® Shaft Grounding Rings for motors of all sizes. Larger motors, above 100 hp/75 kW, would also receive one insulated bearing. AEGIS Rings protect motor and pump bearings from shaft voltage discharge. And an insulated bearing protects motor bearings from the circulating currents that occur in larger machines.
With this protection, the bearings of a drive-fed motor are far less likely to require repair. So specifying electrical bearing protection on all VFD-fed motors will drastically decrease annual repair costs. With repair costs minimized, VFDs will deliver even more of the savings they promise.
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.
