With the increasing popularity of frequency inverters (VFDs), the need to reliably reduce destructive shaft voltages increases, leading to increased demand for bearing protection rings, according to Aegis sales and marketing specialist for storage protection solutions Adam Willwerth .
He explains that bearing rings solve the problem of VFD-induced voltages in motors that can destroy bearings and cause premature downtime.
"Bearings, which normally have a mirror – smooth bearing surface, can be damaged by electrical discharges, without running wave voltages through the bearings and causing unwanted electrical discharges."
Willwerth explains, however, that in most cases that is a reliable and cost-effective way to minimize electrical bearing damage and increase the reliability of VFD-controlled engines and English: v3.espacenet.com/textdoc? The system uses an Aegis bearing protection ring combined with an insulated bearing for large motors larger than 75 kW
In contrast to the previously used shaft grounding technology of a spring – loaded carbon brush, it complements the Aegis – Bearing protection The rings – which are sold worldwide by Electrostatic Technology – offer a much higher level of efficiency, in particular to avoid high-frequency bearing currents.
The bearing protection rings are made of highly conductive microfibers attached to the patented FiberLock channel. Scalable around each shaft diameter, the fibers encircle the shaft of the motor and provide a low-impedance path from the shaft to the frame, he explains. The fibers also provide a low impedance path to the ground, allowing the channel to reliably redirect harmful currents.
Because the microfibers operate with little or no contact with the shaft, they are not subject to wear as conventional carbon brushes, Willwerth notes.
He further explains that the conductive microfibers discharge at each voltage spike and operate at very high frequencies, in the megahertz range, at the switching frequencies of the VLD bipolar transistor (IGBT). He adds that microfibers developed by Electro Static Technology have been specifically designed to discharge VFD induced voltages and high frequency currents.
Willwerth also notes that Aegis-protected motors require no downtime and last about three times longer because the bearings do not degrade due to electrical discharges.
"Shaft voltage is a lifetime for VFD-powered engines, so minimizing electrical damage minimizes engine life and reduces the frequency of bearing replacement, as well as preventing premature and catastrophic engine failure," he says, leading to cost savings and increased productivity for the engine end user.  Willwerth states, however, that shaft grounding in the form of high-maintenance, mechanically suspended carbon brushes was the only solution before Aegis bearing protection rings
"Wave voltages generated by the pulse width modulation of the VFD are capacitively coupled to the stator in the motor Wave. "These tensions reach their maximum at a voltage greater than 10 V and are high enough to overcome the dielectric of the oil film in the bearing. It will then blow through the bearing in a lightning-like discharge that burns the lubrication and causes electrical erosion holes in the storage turf, "explains Willwerth.
This, he adds, happens millions of times an hour and can cause bearing damage due to electrical damage weeks or months of operation only.
The defective bearing will show a washboard pattern, called "fluting" on the barrel, and burnt black grease, which is troublesome and expensive to operate the system, as this leads to premature storage.
Aegis bearing shrouds are therefore a maintenance-free circumferential ring of conductive microfibers that last longer than the design life of the bearings, which is equivalent to 200,000 hours, says Willwerth.
Aegis bearing shrouds have been sold in more than 1 million worldwide two million applications mainly installed in North America and Asia.