In the electrical AC motor industry, the use of variable frequency drives greatly increases generation of electrical current on the shaft of the AC motor and causes electrical damage to bearings unless an effective and long lasting strategy is employed to protect the motor and prevent potential catastrophic failure.

VFD Induced Shaft Currents

Damaging shaft currents are built up on the shafts of AC motors when controlled by variable frequency drives (VFD). The extremely high on/off switching speeds of the pulse width modulation (PWM) generated by the insulated gate bipolar transistors (IGBT), are induced onto the motor shaft as a result of the parasitic capacitive coupling between the stator and rotor. This common mode voltage builds up on the shaft until it finds a discharge path to the motor frame, usually through the motor bearings.

VFD Induced Shaft Currents

These damaging currents cause fusion craters in the bearing through a process known as electrical discharge machining (EDM) and ultimately result in severe frosting, fluting, bearing noise, and premature motor failure. Without protection this phenomenon occurs continuously during operation of the motor/drive system until premature motor failure occurs.

Circulating Currents in large AC and DC motors

In addition to potential bearing failures in motors from VFD currents, larger AC and DC motors with shafts over 2" may also experience bearing failures caused by circulating currents. These circulating currents are a result of magnetic flux imbalances which cause currents to circulate through the motor between shaft and frame and discharge through the motor bearings which provide the path of least resistance.

Circulating Currents in large
AC and DC motors

Because these currents circulate through the motor via the shaft and bearings, the current flow must be either broken or an alternate path established to prevent bearing failures.

Shaft Grounding Technology Comparison: AEGIS Shaft Grounding Ring™ Conductive MicroFiber™ Brush with other common methods

AEGIS Shaft Grounding Ring™ provides a revolutionary solution to extend the longevity of AC and DC motors by actually preventing the destructive electrical bearing discharges which cause premature motor failure. AEGIS SGR™ employs patent pending Electron Transport Technology™ to overcome the obstacles encountered with application of other technologies.

Maintenance free
Low lifetime cost
For any AC or DC motor
Improves Reliability
Easy to install
Long-term effectiveness

	AEGIS SGR™	Insulating sleeve	Ceramic/Hybrid Bearing	Copper or Bronze Metal Brush	Carbon Block Brush	Conductive Grease
Protects Motor and Attached Equipment	Yes	No	No	No	No	No
Long-term Effectiveness	Yes	No*	No*	No	No	No
Easy to install	Yes	No	No	No	No	No
Contamination Proof	Yes	N/A	N/A	No	No	N/A
Low Lifetime Cost High return on Investment	Yes	No	No	No	No	No
Effective at any RPM	Yes	Yes	Yes	No	No	No
Maintenance Free Operation	Yes	Yes	Yes	No	No	No

Protects Motor and Attached Equipment: Destructive shaft currents induced in electric motors will always seek the path of least resistance to ground. Without a safe discharge path for shaft currents, the EDM effect from the discharges result in severe frosting, fluting, bearing noise and premature motor failure. Installing AEGIS Shaft Grounding Ring™ establishes the most reliable continuous discharge path for shaft current and extends bearing life by channeling the currents away from the bearings in the motor and attached equipment.

Ceramic bearings and insulated sleeves prevent current from passing through the bearing race but do not remove voltages and currents from the shaft - these currents then seek an alternate path to ground and will instead discharge through bearings in attached equipment like gear boxes, pillow blocks etc. Insulated sleeves are usually only installed on the opposite drive end of the motor, allowing shaft currents to flow through the drive end bearing or attached equipment.

Conventional spring loaded copper phosphor, bronze, or carbon brushes become ineffective, often within only a few weeks, because oxidation builds up on the shaft and dirt and grease reduce their conductivity leaving the motor unprotected from bearing current discharges. Conductive grease will become less effective over time as the conductive particles separate.

Long-term Effectiveness: AEGIS SGR™ is the longest lasting and most reliable solution available, proven to operate with virtually zero wear during extensive life testing. This is because the special Conductive MicroFibers™ are configured for ultra low friction between the fiber tips and motor shaft, whether in continuous operation or with frequent direction reversals. Conventional grounding brushes wear rapidly and require constant maintenance and replacement. Conductive grease loses effectiveness as particles separate and may cause problems with lubrication in the bearing. *Ceramic bearings and insulating sleeves do nothing to discharge the currents induced on the motor shaft. These currents seek a path to ground, discharging through attached equipment bearings instead. Insulated sleeves also cause greater heat build-up at the bearing which reduces bearing life.

Easy to install: AEGIS SGR™ is easily installed with external mounting brackets that clamp directly on to the motor end bell. Installation may be on the drive end and/or the non-drive end of the motor depending on the application. AEGIS SGR™ may also be press fit into the motor housing. All other technologies require significant machining or motor disassembly to accomplish installation.

Contamination Proof: Effective even in oil, grease, water, dust or dirt, AEGIS SGR™ achieves robust performance even when motors are operated in harsh environments and in virtually all industrial applications. Conventional spring loaded grounding brushes quickly lose their effectiveness when oil, grease, water or contamination is present. Insulating sleeves lose effectiveness if dirt and particles build up or hairline fractures appear in the ceramic coating.

Lifetime cost of solution: AEGIS SGR™ achieves the highest return on investment by improving reliability and preventing destructive shaft currents from causing motor failures. The low initial cost to install AEGIS SGR™ on the motor combined with continuous long-term and maintenance-free performance delivers unequaled value. Ceramic bearings are costly to implement and often require long lead times. Insulating sleeves are costly to install and leave the drive end unprotected in the usual non-drive end installation. Conductive grease loses effectiveness over time and requires replacement which increases maintenance costs. Externally mounted spring loaded brushes require special installation and frequent maintenance and replacement which increase lifetime costs.

Effective at any RPM: AEGIS SGR™ effectively discharges shaft currents at any RPM or surface rate. This makes AEGIS SGR™ highly effective in any application from large motor shafts 6" (152mm) or greater where the surface rate of an 1800 RPM motor is quite high, to spindle motors operating at 15,000 RPM. The Conductive MicroFibers™ completely surround the shaft to protect the motor and ensure reliable shaft current discharge at any surface rate. Conventional spring loaded shaft grounding brushes wear more quickly as surface rate increases and rely on friction from the spring to obtaining a contact with a slipping surface. This connection becomes less effective as surface rate increases and is easily interrupted as oxidation and contamination builds on the shaft.

Maintenance Free Operation: AEGIS Shaft Grounding Ring™ is maintenance free and highly reliable. Once installed AEGIS SGR™ continues to operate without any further adjustment, replacement or maintenance and with no frictional wear over time. Ceramic bearings are installed by motor manufacturers and should not require maintenance. Insulating sleeve may require maintenance if contamination builds up during operation. Conductive grease will require periodic replacement. All types of contact friction brushes (spring loaded copper phosphor, bronze, or carbon) require regular, frequent and careful maintenance and even then may not operate effectively.