AEGIS® Bearing Protection - Why Shaft Grounding?
Bearing Currents
50/60 Circulating Currents from Line Voltage in Motors over 500 Frame:
Sinusoidal voltage sources can cause low frequency circulating currents in large machines due to motors' not-perfectly-symmetical design. 50/60Hz operation can result in circulating currents due to motor magnetic asymmetries.
- Usually present in very large machines only
- Circulate through the motor bearings, shaft to frame
Best Practice: Interrupting the circulating current is the best approach to mitigating potential bearing damage.
Ref: NEMA MG1 Part 31.4.4.3
AC Induction Motors
| VFD OPERATION | NO VFD - 50/60/ Hz line operation |
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| Motors up to and including 100hp (Low Voltage) |
Motors over 100hp to 500 hp (Low Voltage - up to 600 volts AC) |
Motors over 500hp (Medium Voltage- over 600 VAC) |
Motors over 500 Frame (Medium Voltage) |
| Capacitive EDM Current | Capacitive EDM Current High Frequency Circulating Current |
Capacitive EDM Current High Frequency Circulating Current Low Frequency Circulating Current |
50/60 Hz Circulating Current |
AEGIS® SGR |
AEGIS® SGR |
AEGIS® PRO |
AEGIS® PRO (may not be needed) |
Install AEGIS® SGR on DE or NDE |
Install AEGIS® SGR opposite side of bearing insulation; usually DE |
Install AEGIS® PRO Ring opposite side of bearing insulation; usually DE |
Install AEGIS® PRO Ring opposite side of bearing insulation: usually DE |
| n/a | Isolate one bearing, usually the NDE to break the circulating current path. | Isolate one bearing, usually the NDE to break the circulating current path. | Isolate one bearing, usually the NDE to break the circulating current path |