Stop bearing failures before they start: what every maintenance team should know about VFD effects

4 types of damage from current discharge

“From the increased use of variable frequency drives, we’re seeing a lot of customers struggle with current discharge and the imbalances that creates,” Kauer says. When VFDs are introduced into motor systems, they can create electrical imbalances that lead to stray currents passing through motor bearings. Over time, these discharges cause a variety of mechanical and electrical damage patterns.

“Currents are looking for a place to go, and typically, it’ll go right through the motor, through the bearings,” says Mignano.

Stray currents can lead to several forms of bearing damage, and each type leaves behind telltale signs that help reliability teams identify the root cause. Below are four common types of bearing damage caused by current discharge—and how each one develops:

1. With VFD applications, the insulated gate bipolar transistor (IGBT) is the key component that switches at a very high frequency, Kaineg says. “This is the main cause of voltage potential, leading to stray current damaging bearings,” he adds.
2. Fluting is a specific type of bearing damage caused by electrical currents, which can cause ridges or flutes on the bearing raceway. “Fluting is a result of the bearing’s rotation in combination with the IGBT’s high-speed switching. Fluting is not always present, so it is important to examine the raceway/rolling element under magnification to see the electric erosion damage (or melting of the material). Sometimes it is just a frosty gray color,” Kaineg says.
3. Electrical current can also be an issue in terms of lubrication degradation, pitting or cratering, and cracking. “Repeated electrical discharges can create tiny crater-like pits on raceways and rolling elements, which can lead to roughness, increased vibration (and, therefore, noise), and potentially initiation sites for greater damage,” Kaineg says.
4. White etching cracks (WECs) are another issue to watch out for. “Electrical discharges, especially at low current densities, can contribute to the formation of WECs. These microstructural changes in the bearing steel appear white when etched), which can lead to premature fatigue and spalling,” Kaineg says.

Boost bearing reliability with ceramic and hybrid materials

To counter the constant damaging conditions seen by bearings, engineers are turning to advanced bearing materials and designs. Ceramic-coated and hybrid ceramic bearings offer powerful insulation and extended service life in demanding motor applications. These technologies not only block damaging current paths but also reduce friction, enhance lubricant life, and boost overall reliability in critical equipment.

Ceramic coated bearings can help with dry current, as ceramic rolling elements are fantastic insulators. “The term ‘dry current’ is used in contrast to lubricated conditions, typically referring to an electrical current passing through rolling elements and raceways without a sufficient, continuous lubricant film (such as oil or grease) separating the metal surfaces,” Kaineg says. Though no current passes through, he warns to be careful, as the voltage potential still exists. This means currents could flow down the shaft to the driven assets. 

Hybrid ceramic bearings, which have ceramic balls, offer even higher reliability in VFD applications, Kauer says. Hybrid bearings have the same voltage protection, plus improved finish, low mass, and increased hardness, which will provide less stress on the lubricant. “The lubricant lasts much longer, up to three times, so, hybrids are great solution for applications where lubrication might be an issue,” Kaineg says.  

Schaeffler has made significant investment in ceramic bearing industry with the 2022 acquisition of Luxembourg-based Ceraspin, which has been developing and producing ceramic products for 25 years, the majority of which are processed into rolling elements for various bearing applications.

Automated bearing lubrication systems improve reliability and workforce efficiency

Consistent lubrication is key to bearing health, but manual greasing often leads to over- or under-lubrication and inconsistent results. Automated lubrication systems solve this challenge by delivering the right amount of grease at the right time.

Mignano estimates that around 70% of bearings in the field are manually lubricated by technicians on a planned maintenance schedule. Instead, with automatic lubricators, the bearings get more frequent grease applications in smaller quantities. “It’s a much more efficient way to lubricate the bearing, and by doing that, it’s always providing clean grease to the bearing, which is going to extend its life and improve the reliability,” Mignano says.
Schaeffler has been selling automated lubricators for more than 20 years. The Concept One automated lubricator is a gas-powered device that will empty grease into the bearing, based on a set time interval (six month or one year, for example). A few years ago, the company released a Smart Base unit for the automated lubricator to help manage lubrication programs. It gives the status of the lubricator, such as how much time remains before a refill is needed in days or percent full. “The Smart Base will alert you if the temperature is too hot or cold for the lubricant,” Mignano says.

The Smart Base unit can bump the pressure 5 bar under gas power, and a small pump can boost pressure another 5 bar to 10 bar. “We get a little extra push, and it’ll let us know if there’s back pressure. That’s the most critical thing, are we actually getting grease to the bearing, or is the line clogged somewhere?” Mignano asks. “The Smart base measures back pressure and, most importantly, can identify whether the lube line is clogged. This lets the end user know lubricant may not be making it to the bearing, and that a visual inspection is required.” The OPTIME C1 Smart Lubricator was released in 2022 and the new FAG OPTIME C4 (4 port lubricator) was globally launched on Sept 25, 2025. For more on Schaeffler’s OPTIME system and best practices for ceramic bearing installation and maintenance, read this article.

Schaeffler will train maintenance teams on-site with the new technology. “There’s a little bit of a culture change that needs to happen,” Mignano says. Manufacturers can reassign those taking manual measurements to more value-add work, such as planning and scheduling and focuses on proactive maintenance. “It allows for more time for maintenance through that efficiency gain,” Kauer says.

It also helps make operations safer. “Keeping people away from rotating equipment is always a good thing,” Mignano says. Across the board, Schaeffler sees maintenance teams shrinking for many reasons that weigh heavily on the workforce. “There used to be three to five guys in a department, now it’s one guy, maybe two, and they have no time for anything,” Mignano says. “We’re an extension of their reliability team, and they tap into our knowledge and experience in helping them maintain their assets properly.”