motor bearing protection does it work

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it seems to be a hit or miss proposition. my experience with such things is very limited but it always seems to help but does not always eliminate the problem entirely.
 
The system shows how to bond it but is that the best way to dissipate the Voltage/Current. To the motor housing, ground rod or building steel.
 
CBRE said:
The system shows how to bond it but is that the best way to dissipate the Voltage/Current. To the motor housing, ground rod or building steel.
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The induced voltages are between parts of the motor, not between motor windings and any external ground reference.
You need to bond the rotor to the motor housing, and a connection through the EGC to earth is incidental and not significant with respect to motor damage.
Looking at it another way, you want to provide an alternative path between rotor shaft and motor housing that does not go through the bearings to cause pitting.
 
I’ve had one motor fail due to circulating currents. It was on pedestal bearings and the drive end was insulated. Every thing was fine for years until the fitters altered the coupling cover and bolted it to pedestal.
 
They do make a difference. However, not all VFD's will cause problems. You could take 100 motor-VFD combinations at a plant and run them all for 50,000 hours only to disassemble them and find evidence of pitting/fluting on only half of the motors. Prevalence depend on many characteristics including motor conductor lengths (whether the cables are impedance matched between the drive and motor). Mismatched impedance will increase reflected waves. Increase in reflected waves will increase the induced voltage measured on the shaft. The higher the voltage, the more likely an electrical discharge will arc from the shaft to the bearing. The electrical discharges will "machine" millions of tiny holes on the bearing track and burn the grease. Eventually the friction builds up and causes the motor to fail. Providing shaft grounding short circuits the path through the bearings so this machining does not take place. It does not eliminate the reflected waves, however.

Reflected waves can be studied more in transmission line theory, or fields and waves.

ptonsparky said:
Not being an engineer, I picture a brush holder fitted to the bell housing with the brush rubbing on the shaft. Simple as that?
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exactly that
 
ptonsparky said:
Not being an engineer, I picture a brush holder fitted to the bell housing with the brush rubbing on the shaft. Simple as that?
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Yes, I've seen installations like that. How much that mitigates the problem, I don't know. In all my years of dealing with variable speed drives I can't recall any that had bearing problems.
 
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