We are huge advocates of utilizing VFDs to control AC motors in most instances. It isn't often that we need to run a pump motor at full speed, so we can reduce our energy consumption (lower costs) while being a little kinder to our motors by installing VFDs in our systems. Rarely in life do we encounter anything that is flawless, however, and VFDs are no exception. They do lower our operating costs and can increase system performance, but they also create shaft voltage.
Simply put, VFDs induce voltage onto the shaft of the driven motor. This can cause pitting, fluting and, if left unchecked, bearing and motor failure. Addressing motor failure has become a significant problem in HVAC systems and in industrial systems.
"The largest motor manufacturer in the United States has cited eliminating drive-related motor failures as its number one engineering challenge."
(from AEGIS white paper, Preventing VFD/AC Drive-Induced Electrical Damage to AC Motor Bearings)
We are here to help you solve this problem. Well, actually, a company named AEGIS is here to help you solve it. While Heat Transfer Sales does not represent AEGIS products, we are intent on helping engineers solve system problems. From what we've seen, AEGIS products address this problem nicely. AEGIS offers a variety of shaft grounding rings designed to divert bearing currents to ground. They even offer a few free resources for engineers, including technical white papers:
Click here for the full list of white papers and technical resources available from AEGIS.
Take a look at this short video before and after AEGIS Ring installation:
The benefits of using VFDs are numerous, but we want to take care to protect our motors from any side-effects created by utilizing VFDs. If you need questions answered about VFD selection or other equipment, please contact your local manufacturer's representative. We are here to make your life a little easier.