Recently we have a 2400V, 800HP, 3PH, motor (old Louis Allis brand, sleeve bearing, oil ring lubricated, self ventilated) that went thru a rewind. It was a work done to proactively improve the overall insulation quality on the machine. Since then, the motor is making a louder noise. It's hard to quantify how loud but if on the scale of 0-10 (10 being loudest), I'd say the noise level right now is somewhere around 6-7 while the before it was 2-3. The noise is coming from inside the motor and it sounds just like a humming noise in general. We've done all the mechanical/electrical checks that we could do on this motor but found no anomalies. However, when the motor was tested in our local shop, it was okay. Our power supply, load conditions (motor used to drive a high pressure pump) are all the same, so we aren't sure what could be the cause at the moment. I thus wonder if the re-wind could possibily cause some acoustic characteristics to change in the winding? What are other things that we could do to inspect and troubleshoot?
Could re-wind cause motor acoustic characteristic to change?
- Thread starter tankfarms
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cadpoint
Senior Member
- Location
- Durham, NC
I think you gave the answer, it's the sleeve bearings, did they match everything about the orginal characteristic of them ?
How could it not be if everything else is ok?
How could it not be if everything else is ok?
kingpb
Senior Member
- Location
- SE USA as far as you can go
- Occupation
- Engineer, Registered
You need to measure the sound level, dBA. Is it within NEMA MG-1 requirements? It could be that you didn't notice it so much before, but since the rewind, it seems louder, but, it may still be within acceptable limits.
Sierrasparky
Senior Member
- Location
- USA
- Occupation
- Electrician ,contractor
Being a sleeve motor I bet the sleeve was slightly damaged during re-assembly or the bearing is original. Ball bearings are much quieter.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
110819-1618 EDT
Sierrasparky:
Why is a ball bearing quieter than a sleeve bearing?
.
Sierrasparky:
Why is a ball bearing quieter than a sleeve bearing?
.
Thanks all for the feedback. It's interesting as my mechanical folks have double-checked everything and all characteristics are the same. Motor is still runinning at the moment without any issues. They assured the integrity of the sleeve bearing and all the vibration signatures look the same as before.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Assuming this is not on a VFD as that would have been a big enough issue for you to have mentioned.
In general though, it is possible on a number of fronts. I'm not a motor rewind expert but I have been around them for years. The things I have observed that might be an issue are possibly with the bake out causing the laminations to be looser, random windings used in the rewind on a motor designed for formed windings, things like that. Bottom line is that if your rewind specs to the motor shop did not include maintaining the same acoustical profile as the original, they would not have paid the extra attention to detail that would entail. It would have cost you a lot more too. As mentioned by kingpin if it's still within NEMA specs they may be OK, just not what you had before. Take a db reading and check it out before getting too excited about it.
In general though, it is possible on a number of fronts. I'm not a motor rewind expert but I have been around them for years. The things I have observed that might be an issue are possibly with the bake out causing the laminations to be looser, random windings used in the rewind on a motor designed for formed windings, things like that. Bottom line is that if your rewind specs to the motor shop did not include maintaining the same acoustical profile as the original, they would not have paid the extra attention to detail that would entail. It would have cost you a lot more too. As mentioned by kingpin if it's still within NEMA specs they may be OK, just not what you had before. Take a db reading and check it out before getting too excited about it.
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