In today’s manufacturing environment, Variable Frequency Drives (VFDs) are standard tools for controlling motor speed and saving energy—but they introduce a hidden reliability risk. High-frequency shaft voltages generated by VFDs can discharge through motor bearings, causing pitting, fluting and premature failure. The real pain point for operators is unplanned downtime, not just broken bearings. That’s where AEGIS® Shaft Grounding Rings come in. They provide a safe path for shaft voltage to ground, helping protect bearings and keep your system running. For larger motors (over 100 HP), best practice is to isolate one bearing and install the grounding ring on the opposite end for complete protection.
Key Takeaways
- Premature failure of critical motors causes the huge expense of unplanned downtime.
- Variable Frequency Drives (VFDs) can enhance motor control and save energy, but they also create damaging shaft voltage.
- Shaft voltage discharges through bearings, causing pitting, fluting, and premature failure.
- AEGIS® Shaft Grounding Rings give the voltage a safe path to ground, protecting bearings and uptime.
- For motors over 100 HP, isolate one bearing and install a grounding ring on the opposite end for complete electrical bearing protection.
VFDs and Electrical Bearing Damage
Variable Frequency Drives (VFDs) are widely used to control motor speed and reduce energy costs. However, VFDs produce a high-frequency common-mode voltage. This voltage couples onto the motor shaft, producing a capacitive shaft voltage.
If there is no lower-impedance discharge path, the shaft voltage may arc through the bearings. This arcing creates tiny pits on the bearing raceways. Over time, these pits roughen the raceways, increasing friction, heating, and vibration, and ultimately causing early bearing failure.
In larger motors, VFDs also produce a high-frequency circulating current that causes the same kind of electrical bearing damage.
How AEGIS Shaft Grounding Protects Bearings
An AEGIS Shaft Grounding Ring surrounds the motor shaft with 360° of conductive microfibers. These microfibers continuously bleed off shaft voltage before it can discharge through the bearings.
Because the fibers touch lightly with virtually no friction, wear is negligible and they typically require little to no maintenance once installed. Lab testing suggests a potential wear life of up to 200,000 hours; however, real-world performance is likely to be shorter. Even so, the ring’s life far outlasts the L10 life of the bearing.
Best Practices for VFD-Driven Motors
Follow manufacturer guidance. Always adhere to the VFD manufacturer’s recommended installation and grounding procedures.
Install an AEGIS Shaft Grounding Ring. Select the correct AEGIS ring for your motor size and a convenient mounting method. Options include solid, split, clamp-on, epoxy-mounted, and universal kits for easy retrofits.
Enhance shaft conductivity. Apply a conductive shaft coating to improve the effectiveness of shaft grounding.
For motors over 100 HP: Use one insulated or ceramic bearing to interrupt circulating current, and install an AEGIS Shaft Grounding Ring on the opposite end to ensure complete protection.
FAQs: VFD Bearing Protection
Q: Do all VFD-driven motors need shaft grounding?
Yes. Any VFD-controlled motor is at risk of shaft voltage discharge. Grounding rings are a preventive measure to avoid bearing damage.
Q: Can I install an insulated bearing and shaft grounding at the same end of the motor?
No. If an AEGIS ring (or other shaft grounding device) is installed at the insulated bearing end, circulating current will pass through the ring and arc through the opposite bearing. Always install shaft grounding opposite the insulated bearing.
Q: Can shaft grounding rings be retrofitted to existing motors?
Yes. Split rings, clamp-on designs, and epoxy kits make it easy to retrofit AEGIS rings onto motors already in service.
Protecting Your Motors Before Failure Happens
Unplanned downtime is not an option for businesses, from data centers to hospitals to paper mills. Installing AEGIS Shaft Grounding Rings is one of the simplest, most cost-effective steps you can take to reduce your risk of unplanned downtime.
Electro Static Technology, an ITW company, proudly manufactures AEGIS Shaft Grounding Rings in Maine, USA. Explore our applications page or request a quote to learn how AEGIS can help keep your motors running reliably.
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 monthly live training webinars, and we can also visit your facility to review your exact application.
