Causes for high vibrations in all 3 axes at both bearings in 2 pole, 3000 RPM, 50 Hz motor 5

[edison123]

What could be the reasons for high vibrations in all 3 axes at both bearings in 2 pole, 3000 RPM, 50 Hz motor as given below?

These are uncoupled/open shaft vibration readings.

Thanks for inputs.

Motor DE Vertical

Motor DE Horizontal

Motor DE Axial

Motor NDE Vertical

Motor NDE Horizontal

Motor NDE Axial

 

[electricpete]

a few thoughts:

Velocity looks a little higher on the NDE. Acceleration TWF peaks look a lot higher on the NDE. That seems to rule out a few things like coupling problem or misalignment and focus attention toward the NDE.

Spectra show 1x and harmonics on all positions. There looks to be some low level non-sync peaks that are near each harmonic starting out around 8x and continuing to 20x. Can you identify the frequency pattern of those? (put on log scale or change to acceleration to make those peaks more prominent, and label the peaks). Do those correspond to pole pass spacing or some other identifiable pattern?

TWF shows some interesting features, periodic at 1x but multiple impacts per revolution, not necessarily equally spaced within a revolution (but same spacing for every revolution).

Is there anything special about most recent reading where DE Horizontal decreased (after increasing just before that)? Or seemingly a random change?

What type of bearings does this machine have?

Is it an induction motor? Open construction or tefc?

Just for general info, what is the hp and what is the machine driving? (it probably doesn't make a difference but makes it easier to visualize the machine we're talking about).

at this point it has the appearance of some kind of looseness (or less likely some other type of impacting) near the NDE for what that's worth. The options I'd think about are first external inspection for looseness including at the support. If nothing found there then tagout the machine for further inspections of bearings, fits, bearing clearances if applicable for sleev bearing, any fan, and maybe rotor near the nde. Answers to questions might change my swag and recommendations a little, or maybe not.

 

[cranky108]

2 pole, but how many phases? Did you lose a phase?

 

[edison123]

Thanks, pete. It's 1200 KW motor with white metal bearings. Sorry should have mentioned the bearings.

Works including stator rewinding, shaft replacement and 'recentering of rotor with end shields on dowels due to rub issues' and some other works on bearings were done in another repair shop about which I do not have full info.

Have asked the client to send the motor my shop. I suspect bent or out of center shaft or white metal bearings issues. Do you agree?


cranky

It's a 3 phase, 2pole, 3000 RPM, 1200 KW decoupled motor with no phase loss.

Muthu

http://www.edison.co.in

 

[Tmoose]

So this is a freshly re-built motor ?

 

[cranky108]

The thing about freshly re-built motors and generators is they use grease in the winding of them, so they may emit smoke as they heat up. It is not a failure but maybe concerning.

 

[Gr8blu]

edison123 Given the power/speed combination, it is possible that either original or replacement rotor is a "flexible shaft" design - which means the "other" shop may have balanced the thing incorrectly in the first place. A result of that might have been to initiate a rub between shaft and endshield / baffle. And THAT Might lead to localized heating and further distortion of the shaft "trueness" if occurring for a long enough period of time.

By the way - it's been a long time since I saw/heard the term "white metal bearing". I (almost) had to look it up!

Converting energy to motion for more than half a century

 

[electricpete]

It seems very plausible to me that this vibration does indeed represent a bow. I imagine that with a U shaped bow, the load will alternate from outboard end of each bearing to inboard end of each bearing, and that could resemble an impact-like event occurring twice per revolution as the load slaps onto the two ends of each bearing. But it's not perfectly regular for a variety of reasons like maybe there is an element of "falling" once per rev when it gets past an unstable point with the U inverted... so it's easy to imagine that those two impacts per revolution are not the same magnitude as each other and are not equally spaced within the revolution. And that's exactly the pattern we see in a lot of your TWFs. For example big impact after 11 msec, little impact 9 msec later, big impact 11 msec later, little impact 9 msec later, big impact 11 msec later, little impact 9 msec later (the pattern has two impacts each 20msec revolution, but it's not periodic at 10msec).

I'd keep the looseness in mind if bow doesn't pan out, but bow does seem like the likely candidate.

Let us know what you find

 

[TugboatEng]

I can't offer anything technical here, way out of my league on this one. only anecdotal but some years back I do remember reading a paper published by GE for their marine steam turbines. The rotation speed was double at around 6k rpm but I don't know how shaft diameters compare. The engineers had determined there was some breakdown of the hydrodynamic wedge which caused the shaft to pound in the bearing causing vibration. The problem was resolved by cutting an axial groove in the bearing surface.

Here is the closest article I can find but I don't think it resembles your bearing configuration.

https://www.kingsbury.com/pdf/journal-bearing-vibration-and-ssv-hash.pdf

 

[edison123]

Thank you all for your tips.

If and when the motor reaches our shop, will do detailed checks and update here.

Muthu

http://www.edison.co.in

 

[wcaseyharman]

Not a vibration expert by any means, but to me that steep unsymmetrical acceleration looks a lot like a rub on the NDE. I see similar but less pronounced vibration in the other bearing and axis at the same time, which makes me believe that whatever is happening on the NDE is “ringing” the whole motor. Since it sounds like this motor had rubbing issues previously it seems even more plausible. If the motor has an integral rotor fan I would look at fan/fan shroud contact. Just my $0.02.

Casey

 

[Strong]

Probably a combination of two things:
1) Excessive dynamic force at 1xSS from rotor unbalance -- poor shop job or change during service
2) Excessive bearing clearance or loose bearing liner

Probably requires a trip to the shop (a different one!) unless thiese issues can be verified and corrected at the plant.

Walt

 

[edison123]

Thanks guys. The client is still deciding.

Nice to hear from you after a long time, Walt. Hope you are doing well.

Muthu

http://www.edison.co.in

 

[nilesh cm]

good to see walt strong and electripete on this forum....maintenanceforums.com is no more i guess....

 

[CelsoSC]

Hello,

Sorry for the silly question, what is Motor DE / NDE?
Is it Drive End and Non Drive End ?

And what hardware/software setup is used for the Motor Vibration Analysis?

 

[edison123]

Yes, drive end and non-drive end.

The spectrum came from client's vib analyzer.

Muthu

http://www.edison.co.in

 

[electricpete]

And what hardware/software setup is used for the Motor Vibration Analysis?

There are a wide variety of products available, but if you're asking about the specific hardware/software to produce those particular plots, I can tell you because I recognize it as the same software that we use. Those graphs were produced with CSI / Emerson Machinery Health Manager software, which is typically paired with a CSI / Emerson data collector like their model 2130 or 2140