Shaft Grounding

Variable frequency drives (VFDs) enable precise speed control and significant energy savings, but they can also cause motor bearing failure. VFDs take smooth electric power and break it up into pulses. These pulses create a voltage imbalance in the motor that can build up on the shaft. This shaft voltage can discharge through the bearings, causing cumulative damage and premature motor failure.

These destructive discharges can be seen with a digital oscilloscope equipped with a conductive microfiber probe tip, like the AEGIS® Shaft Voltage Tester™. A typical bearing discharge is shown on the left below, where voltage gradually builds up to several volts (~20V here) and then suddenly collapses back to baseline.

meter readings

Shaft voltages on a motor before (left) and after (right) installation of an AEGIS® Shaft Grounding Ring. The voltage scale is the same in both images.

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Electrical Supervisor Randy Riebel could not believe his ears. The huge ball mill at Monarch Cement Company’s Humboldt, Kansas, processing plant was making that sound again – the piercing squeal of fluted bearings. Riebel had replaced the bearings on the 5000 HP motor that drives the mill three times already! And he knew that the sound meant he would need to replace them again. What he didn’t know was how to prevent the damage from happening again in the future.

Cement Ball MillThe massive ball mill is capable of crushing 100 tons of clinker per hour. “We kept greasing those bearings, but they kept on squealing,” Riebel recalls. “We knew that if we waited too long, the bearing race walls would become fluted like they had in the past, and we weren’t looking forward to another replacement because of all the expense and downtime. It takes at least 10 days to pull that motor – it’s a major production. Sometimes we have to hire help, rent a hoist to put it on a truck, and take it away to be rebuilt.”

So this time Riebel decided to try something different. He had a local motor repair shop install an AEGIS® PRO Series ring on the mill’s motor. A larger version of the AEGIS® Shaft Grounding Ring, the PRO Ring is designed to protect the bearings of high-current and medium-voltage motors. With several rows of conductive microfibers that completely surround the motor shaft, it provides a path of least resistance for damaging shaft currents, channeling them safely to ground.

After the PRO was installed, Riebel took shaft voltage readings. They were very low, indicating that the ring has reduced damaging shaft voltages to negligible levels. Riebel noted, “The last set of bearings only lasted a year. But so far, we haven’t had any squealing.”

To read the full Monarch Cement case study, click here.

For more information on AEGIS® PRO Series Rings, click here.

PRO Series Rings Have 6 Rows of Conductive Microfibers for Maximum Bearing Protection

Shaft protection ring

AEGIS® PRO Series Rings protect large
medium-voltage AC motors (as well as
large low-voltage AC and DC motors) from
VFD-induced bearing damage. The AEGIS®
PROSL (shown above) and all AEGIS® PRO
Series Rings have 6 rows of conductive
microfibers that provide the high current-
carrying capacity needed for these large

New AEGIS® PRO Series Rings are specially designed to protect medium-voltage motors, generators, and turbines as well as large low-voltage AC motors (over 500 HP) and large DC motors (over 350 HP) from damaging VFD-induced shaft voltages and bearing currents.

Available in solid- and split-ring versions for shaft diameters from 2″ (50mm) to 31.5″ (800mm), these rings have 6 rows of conductive microfibers that completely encircle the motor shaft, providing many millions of contact points that channel harmful shaft voltages away from motor bearings and safely to ground.

Solid AEGIS® PRO Rings are ideal for installation on new motors before they are put into service or in-service motors when they are repaired.  Split PRO Rings are designed for fast, easy field installation around the shaft of a coupled motor.

The new product line includes:

AEGIS® PROSL: Available in solid- and split-ring versions for shafts of 2″ (50mm) to 16.6″ (400mm) in diameter.  It has a maximum OAL of 0.650″ (15.88mm).

AEGIS® PROSLR: Specially designed for severe-duty environments, the AEGIS® PROSLR is also available in solid- or split-ring versions for shafts of 2″ (50mm) to 16.6″ (400mm).  To ensure maximum operating reliability in severe environments, it includes an O-ring barrier installed on its front and back faces to protect from the ingress of contamination.  It has a maximum OAL of 0.750″ (19.05mm).

AEGIS® PROMAX: Designed to protect the largest motors and generators, the AEGIS® PROMAX is a split ring for shafts of 16.6″ (400mm) to 31.5″ (800mm) in diameter.  With a maximum OAL of 1.545″ (39.24mm), each AEGIS® PRO MAX Ring is custom designed for the specific application.

AEGIS® PROMR: Combines an AEGIS® PROSL bearing protection ring with an AEGIS® SGR monitoring ring (separated by an insulated phenolic spacer) in a single assembly.  Available in solid- and split-ring versions, it provides bearing protection and real-time monitoring capability for remote or hard-to-access motors.  Available for shafts of 2″ (50mm) to 16.6″ (400mm), it has a maximum OAL of 1.312″ (33.32mm).

Universal Mounting Brackets: Designed to accommodate shaft shoulders, slingers, or other motor face protrusions, Universal Mounting Bracket Kits speed and simplify mounting of all AEGIS® PRO Series Rings.

AEGIS® PRO Series Rings are designed to protect larger motors in processes and applications where the cost of bearing damage, motor repairs, and downtime can be staggering.  Don’t risk motor damage and the high cost of lost production.  Protect your large motors with AEGIS® PRO Series Rings!

For more information on AEGIS® PRO Series Rings, click here.

For Return on Investment Analysis on AEGIS® PRO Series Rings, click here.

To download a copy of the new Edition 3 Bearing Protection Handbook with complete information on new AEGIS® PRO Series Rings, click here.

The AEGIS® Shaft Voltage TesterTM is available in different packages including different accessories and warranties.

The AEGIS® Shaft Voltage TesterTM is
available in different packages including
different accessories and warranties.

Electro Static Technology is announcing the launch of its new AEGIS® Shaft Voltage TesterTM Digital Oscilloscope– ready to ship now!

Ready to use out of the box, this 100 MHz oscilloscope comes preconfigured to take shaft voltage measurements and includes everything you need to test voltage levels on the spinning shaft of a motor.  It displays digital shaft voltage readings on its high-resolution color display as soon as you touch the motor shaft with the specially designed AEGIS® Shaft Voltage Probe. With dual inputs, the unit combines oscilloscope, multimeter, and recorder functions in a single unit.

A probe with special 1:1 and 10:1 settings includes special conductive microfiber tips for exceptional shaft contact, as well as a probe holder with a magnetic base, and a compact carrying case.

Advanced functions of this 2-channel digital oscilloscope include sampling rates of 1 GSa/s to 50 GSa/s, and a 5-hour rechargeable/replaceable lithium-ion battery pack. The oscilloscope accommodates standard set-up interfaces, including removable flash USB drives for easy image capture and storage.

A special AEGIS® One-Touch™ screen capture feature allows recording readings with a push and hold of just one button.  Simply pushing and holding the “Save” button for 6 seconds captures screen images to a USB, simplifying data collection for reporting/analysis and eliminating the need to plug the scope into a computer.

The AEGIS® Shaft Voltage TesterTM Digital Oscilloscope can be configured for a variety of languages including English, French, German, Russian, Spanish, Simplified Chinese, Traditional Chinese, Portuguese, Japanese, Korean, Italian, and Arabic.

Replacement probe tips and spare batteries are also available.

All AEGIS® oscilloscopes are backed by a 90-day warranty.  A 2-year extended warranty is also available.

For more information on the new AEGIS® Shaft Voltage TesterTM Digital Oscilloscope, click here, or see the Shaft Voltage Testing section of Edition 3 of the AEGIS® Bearing Protection Handbook.