3 Phase Motor premature bearing failure
3 Phase Motor premature bearing failure
(OP)
We have a 480VAC 3 phase, 1/2 HP motor that has failed in a very short period of time. The bearing are making a lot of noise. The site is telling us that the motor current is within the normal range. We don't think it is gear drive to which it is connected. My question. I have been putting phase monitors in a lot of our controls as required by spec. I understand the concept of the 3 power phases potentially getting out of phase, but what does that do to the motor? What would the symptoms be?
Thanks in advance!
Thanks in advance!
"To be or not to be, that is the question" - William Shakespeare via Hamlet





RE: 3 Phase Motor premature bearing failure
Is this motor on a VFD by chance? If so, you may have a bearing current issue that needs addressing through the use of an insulated bearing and/or a shaft grounding brush arrangement.
I have read mention of bearing currents being a problem even with DOL started motors in facilities with lots of non-linear loads (there was another thread here recently that addressed this, but I can't find it right now).
To answer your question regarding phase monitors, they will tel if you loose a leg to the motor; an already rotating motor can still continue to turn with a dropped phase, albeit with lower torque and much more generated heat. I don't believe a dropped leg would damage bearings.
Have you taken the bearing apart? Does it appear to have "fluting?" Have a look at the attached white paper from Baldor regarding bearing currents and the issues that arise.
-SceneryDriver
RE: 3 Phase Motor premature bearing failure
There are many possible causes of bearing failure. Best approach is look at the bearing for starters.
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(2B)+(2B)' ?
RE: 3 Phase Motor premature bearing failure
"To be or not to be, that is the question" - William Shakespeare via Hamlet
RE: 3 Phase Motor premature bearing failure
I've pulled the below figures from some notes I had lying around.
% Voltage Imbalance ------- % Temperature Rise
2% ------------------------------ 8% hotter
3% ------------------------------- 18% hotter
4% ------------------------------- 32% hotter
5% ------------------------------- 50% hotter
RE: 3 Phase Motor premature bearing failure
If there is no VFD in use, then the second most common cause of bearing failure in an otherwise well maintained motor is misalignment. The longer the motor runs, the more critical the alignment becomes and for motors that must run continuously for long periods, the best practice is to get a laser alignment now.
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RE: 3 Phase Motor premature bearing failure
"To be or not to be, that is the question" - William Shakespeare via Hamlet
RE: 3 Phase Motor premature bearing failure
you said you don't think the gearbox attached is the issue.... as Jraef said, you most likely have a shaft alignment issue.
if it were phase, voltage, or any other electrical thing, the motor would get hot and damage would likely be to windings, not a mechanical noise issue. mech noise = bearings.
only other likely reason is you have one of those $ 20.00 Cheap motors with cheapo bearings that cannot survive more than a few hundred hours.
You have an alignment issue.