Motor making loud noise, but no obvious mechanical/electrical issues.

[tankfarms]

Hello,
We have a motor that just went through a rewinding/VPI recently, and when it was installed back to service, the noise it?s making is quite louder (I want to say maybe 5 to 8 times more). This motor is used to drive a pump, and its specs are 450HP, FLA 108A, 2.4KV. Mechanical checked all vibrations found no issues and electrical also check the load, and everything is balanced. I thus wonder if the fact that the motor went through the rewind now caused some change inside the windings? Wonder what more can we check when the motor is in service. Any advice?

 

[bphgravity]

I would say either (A) - the rehab on the motor has created an internal noise source that was not present before the rehab or (B) - the motor is now operating properly after the rehab and much louder than the poorly operating motor pre-rehab.

My money would be on (A)...

 

[tankfarms]

I would say either (A) - the rehab on the motor has created an internal noise source that was not present before the rehab or (B) - the motor is now operating properly after the rehab and much louder than the poorly operating motor pre-rehab.

My money would be on (A)...

um.. interesting. Thanks for sharing your opinion on this. We have other two identical motors operating under the same conditions with the same pumps they're driving, they don't have this noise issues, and they're the ones I used as a base to rough estimate the sound now is about 5 to 8 times louder.

the ultimate goal here is of course to understand if there are any threats with this elevated noise on the machine, that's where we kinda got stuck since mechnical/electrical both checked out okay.

 

[richxtlc]

um.. interesting. Thanks for sharing your opinion on this. We have other two identical motors operating under the same conditions with the same pumps they're driving, they don't have this noise issues, and they're the ones I used as a base to rough estimate the sound now is about 5 to 8 times louder.

the ultimate goal here is of course to understand if there are any threats with this elevated noise on the machine, that's where we kinda got stuck since mechnical/electrical both checked out okay.

The rewind may have changed the magnetic characteristics of the motor. the coils may not have been wound the same way as the original, or may not be installed inn the slots exactly the same way.

 

[Besoeker]

Hello,
We have a motor that just went through a rewinding/VPI recently, and when it was installed back to service, the noise it?s making is quite louder (I want to say maybe 5 to 8 times more). This motor is used to drive a pump, and its specs are 450HP, FLA 108A, 2.4KV. Mechanical checked all vibrations found no issues and electrical also check the load, and everything is balanced. I thus wonder if the fact that the motor went through the rewind now caused some change inside the windings? Wonder what more can we check when the motor is in service. Any advice?

Maybe the new windings are not as well secured in their slots and the possible movement is the source of noise?

 

[ptonsparky]

Can you run the motor without the pump attached? We have had items stuck in the pump that has caused grief. Not near 450 hp though. I would think vibration checks would have found that though.

 

[tankfarms]

Maybe the new windings are not as well secured in their slots and the possible movement is the source of noise?

Possible. But this noise is nothing more like the regular motor "humming" during running, except it's louder. Also, it is continous not something pulsive. So rather than being loud, everything else seems to be fine.

 

[stew]

If possible check to see if the other units which are the same have baffle plates at each end of the inside of the motor. If they do and the plates were left out the ambient rotor air noise may be causing the difference in sound.

 

[Besoeker]

Possible. But this noise is nothing more like the regular motor "humming" during running, except it's louder. Also, it is continous not something pulsive. So rather than being loud, everything else seems to be fine.

Sometimes, just sometimes, I look at what has actually been posted. And sometimes think about it.
At 450 hp it's quite a big motor and presumably matched to the pump.
Such an arrangement would already make a lot of noise. I'm going to a pumping station on Friday. There are three 600 kW (800hp) sets with usually only two running at any one time. You can't hear yourself think. Conversation is pretty much impossible.
So, if the motor you mention is generating sufficient noise to stand out from the background ambient, maybe there is cause for concern.

Can you get the rewind company in to listen to it? I don't suppose they'd be overly keen to accept any kind of liability but maybe they could offer some explanation for the increased noise.

In short, my feeling on this is that it's too serious to ignore.
A 450 hp motor can't be considered a consumable.

 

[tankfarms]

Sometimes, just sometimes, I look at what has actually been posted. And sometimes think about it.
At 450 hp it's quite a big motor and presumably matched to the pump.
Such an arrangement would already make a lot of noise. I'm going to a pumping station on Friday. There are three 600 kW (800hp) sets with usually only two running at any one time. You can't hear yourself think. Conversation is pretty much impossible.
So, if the motor you mention is generating sufficient noise to stand out from the background ambient, maybe there is cause for concern.

Can you get the rewind company in to listen to it? I don't suppose they'd be overly keen to accept any kind of liability but maybe they could offer some explanation for the increased noise.

In short, my feeling on this is that it's too serious to ignore.
A 450 hp motor can't be considered a consumable.

You're absolutely right. In this case, the motor is generating enough noise to distinguish itself from the other two identical 450HP machines right next to it. In addition, this is a low speed, low pressure water pump it drives. We know that during normal operation, it's not that noisy at all. This is how I estimated 5~8 times the noisy level as compared with before.

Actually, the motor shop will have a technician come out tomorrow, we'll see how that goes. Not sure if we can convience them to re-do any work as we don't have any technical data to show any abnormal conditions rather than the fact that it's real loud now.

 

[BJ Conner]

Magnetic zero?

Magnetic zero?

IS this a vertical pump motor?
Could the magnetic zero have changed?
When you start the motor does the shaft move in or out (or is it trying to and can't).
If it did I would expect more than noise but when you get into it's a black art.

 

[tankfarms]

IS this a vertical pump motor?
Could the magnetic zero have changed?
When you start the motor does the shaft move in or out (or is it trying to and can't).
If it did I would expect more than noise but when you get into it's a black art.

This is a horizontally placed motor driving a centrifugal water pump.

I can say the motor went in the exact same way as it came out. But details such as the shaft movement you mentioned is hard to tell as we simply don't have that information.

 

[Besoeker]

You're absolutely right. In this case, the motor is generating enough noise to distinguish itself from the other two identical 450HP machines right next to it. In addition, this is a low speed, low pressure water pump it drives. We know that during normal operation, it's not that noisy at all. This is how I estimated 5~8 times the noisy level as compared with before.

Actually, the motor shop will have a technician come out tomorrow, we'll see how that goes. Not sure if we can convience them to re-do any work as we don't have any technical data to show any abnormal conditions rather than the fact that it's real loud now.

Did the technician shed any light on the problem?

 

[tankfarms]

Just some updates
we had the motor rewind shop tech come out and did another round of checking/vibration measurement/listening, etc., we still couldn't get a clear understanding yet what could be the cause.

Next step is to de-couple the motor from the gear, and solo run it and see what that gives us. But field technicians already informed that the motor was making louder noise before they coupled it up, but no engineer was there to verify with measured vibration data, so we're gonna give a try again.

 

[tankfarms]

Updated some info

Updated some info

Here's a screenshot of the vibration spectrum taken while the motor was running. NOt sure if anything relevant can be revealed from this.

 

[GeorgeB]

Here's a screenshot of the vibration spectrum taken while the motor was running. Not sure if anything relevant can be revealed from this.

There does not seem to be any 20, 30, or 60 Hz components in the vibration but I don't see the motor speed anywhere, nor your location to guess at 50Hz or 60Hz. The frequency for 20, 30, and 60 Hz would be 1.2, 1.8, or 3.6 kCPM. They also don't seem to be higher frequency harmonics of those ... 3 phase would have components at triple those rates.

My guess is that the report's vibration is either from the pump, or from some bearing issue. I've not done enough to make an intelligent guess at what stator lamination vibration characteristics would be. If an antifriction bearing, vibration from them tends to be "balls or rollers * RPM", and we see no obvious integral multiples of logical speeds.

Vibration analysis of the bare motor might be useful.

I've seen alignment and coupling issues cause noise and vibration; I assume your millwrights do enough of that to have been sure it was done correctly.

 

[Besoeker]

If the frequency given in kCPM kilocycles per minute?
Assuming that to be the case, I can't see how any of the peaks relate to an electrical frequency.
Except maybe the 1.774 which is quite close to half supply frequency.
But normally you'd expect effects from supply frequency to be multiples of it rather than sub multiples.
Sounds like a mechanical issue.
Re-assembled differently? Shaft driven fan a bit loose?

 

[wiigelec]

What are you pumping? Maybe it is a process issue...

 

[tankfarms]

There does not seem to be any 20, 30, or 60 Hz components in the vibration but I don't see the motor speed anywhere, nor your location to guess at 50Hz or 60Hz. The frequency for 20, 30, and 60 Hz would be 1.2, 1.8, or 3.6 kCPM. They also don't seem to be higher frequency harmonics of those ... 3 phase would have components at triple those rates.

My guess is that the report's vibration is either from the pump, or from some bearing issue. I've not done enough to make an intelligent guess at what stator lamination vibration characteristics would be. If an antifriction bearing, vibration from them tends to be "balls or rollers * RPM", and we see no obvious integral multiples of logical speeds.

Vibration analysis of the bare motor might be useful.

I've seen alignment and coupling issues cause noise and vibration; I assume your millwrights do enough of that to have been sure it was done correctly.

Thanks. This motor's is 890RPM. (which is kinda odd, I would assume it's a 8-pole machine, then rpm 900). I will have to verify when exact and at where this vibration was taken.

You said you've done enough to know what the lamination vibration characteristics would be, so could you share some light on that?

 

[tankfarms]

If the frequency given in kCPM kilocycles per minute?
Assuming that to be the case, I can't see how any of the peaks relate to an electrical frequency.
Except maybe the 1.774 which is quite close to half supply frequency.
But normally you'd expect effects from supply frequency to be multiples of it rather than sub multiples.
Sounds like a mechanical issue.
Re-assembled differently? Shaft driven fan a bit loose?

How did you come to see that 1.774 is quite close to half supply frequency (30Hz)?