bearing damage like current machining in dol motor
bearing damage like current machining in dol motor
(OP)
hello,
we have a hot water pump with a 690V 500kW 4 pole squirrel cage induction motor that had many bearing failure apparently as the ones caused by vfd's but strangely it is a DOL motor, without vfd.
The thing is that mechanical guys changed the non drive end bearing and installed insocoat skf bearing, and since then there was no vibration climbing and apparetly this was the final solution.
Im looking to the cause of this failure, and if anyone have any suggestion to measure it would be much appreciated.
in the main mcc we have 4% THD voltage.
regards,
martin
we have a hot water pump with a 690V 500kW 4 pole squirrel cage induction motor that had many bearing failure apparently as the ones caused by vfd's but strangely it is a DOL motor, without vfd.
The thing is that mechanical guys changed the non drive end bearing and installed insocoat skf bearing, and since then there was no vibration climbing and apparetly this was the final solution.
Im looking to the cause of this failure, and if anyone have any suggestion to measure it would be much appreciated.
in the main mcc we have 4% THD voltage.
regards,
martin





RE: bearing damage like current machining in dol motor
The other, and more probable, failure mechanism is that you have a so-called "frame voltage". The signification of that is that there is a voltage differential between motor stator (frame) and the driven machinery. That can be caused by voltage drop in long PE conductor - or by any other of a number of mechanisms. The remedy here is to bond motor frame to driven machinery so that voltage difference is eliminated.
Can you describe the installation a little fuller?
Gunnar Englund
www.gke.org
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Half full - Half empty? I don't mind. It's what in it that counts.
RE: bearing damage like current machining in dol motor
the coupling to the pump is made of hard rubber it should be insulated, anyway the pump bearing didn't have any problem.
this is an actual photo, we have also shaft earthing but is in bad shape, I don't think it's working.
but the insocoat made the job, later i'll attach the condition monitoring graphs.
RE: bearing damage like current machining in dol motor
RE: bearing damage like current machining in dol motor
Could a slightly asymmetrical rotor or stator or windings cause shaft currents?
Thanks
Bill
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"Why not the best?"
Jimmy Carter
RE: bearing damage like current machining in dol motor
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: bearing damage like current machining in dol motor
Going with Bill'd thought.
Do you know if stator laminations are segmented or one-piece? The latter should have insulated bearings. I've heard 2nd hand that rotor bar problems can cause currents also (long shot)
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(2B)+(2B)' ?
RE: bearing damage like current machining in dol motor
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(2B)+(2B)' ?
RE: bearing damage like current machining in dol motor
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(2B)+(2B)' ?
RE: bearing damage like current machining in dol motor
On the other hand, the fact that we insulated only one bearing and made the problem go away (if true) does seem to tell us something.
I think it would rule out static electricity, frame voltage, common mode power supply influences. Most of what's left I think would be magnetic asymmetry I think. Please correct me if I'm wrong.
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(2B)+(2B)' ?