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High vibration during motor solo run

High vibration during motor solo run

High vibration during motor solo run

Motor Details : 1200 kW @ 3000 rpm with sleeve bearing (proximity probes mounted on bearing)
Observation :
Offline Casing vibration monitoring system:
1) Observed overall vibration readings are on higher side 4.4 mm/sec peak.
2) Dominant vibration observed at 2X CPM (2.80 mm/sec peak) & multiples of shaft running speed.
3) After loosening the bolt, casing vibration drop down to 2.5 mm/sec peak.
4) Vibration varies from 3.5 to 4.4 mm/sec peak.

Online (Bently Nevada) vibration monitoring system:
1) Observed radial vibration readings are on higher side i.e. 80 to 85 micron pk-pk (Y probe showing high vibration as compared with X probe on both bearings).
2) Dominant vibration observed at 1X CPM & multiples of shaft speed.
3) Also during loosening the bolts, radial vibrations are drop to 65 micron pk-pk.
4) Observed orbit shape is elliptical.
5) Vibration observed at slow roll speed is less than 20 micron pk-pk.

As per my opinion, i suggest that to check blue matching for rectification of motor soft foot.

What are other sources of vibration?

RE: High vibration during motor solo run

I'm guessing the motor construction is something like this -


Please reply to all the following questions, in full.

Is the motor being run solo on a test bed, in a repair shop?
Or, is the motor being run solo in its natural habitat, just uncoupled from the pump, fan or whatever?

Please post some vibration spectra showing frequencies up to 10X rotation from prox probes and casing measurements.
Please post some vibration spectra taken vertically on all (4?) motor feet, and all 4 motor hold down bolts,
Please post some vibration spectra taken vertically on the base plate near all 4 motor feet.

Please measure and record the 1X and 2X vibration amplitude and phase on all 4 motor feet, all 4 hold down bolts, and adjacent to each motor foot on the base plate.

Why was it run solo?
(I'm guessing because the in service vibration had caught someone's attention)

How was the motor's coupling half restrained when running solo?

"After loosening the bolt, casing vibration drop down to 2.5 mm/sec peak."

Which bolt was loosened?

A Bearing insert with insufficient crush/loose fit in its housing can cause some pretty interesting vibration results.

Is there Any historical vibration data to share?
How does it run coupled, in service?
What is the maintenance history of this motor?

RE: High vibration during motor solo run

Not sure what type of coupling you have in your application. I would first check the hub flange run-out while rotating the motor shaft. At 3000 rpm, you want to have a maximum of 0.002" run-out, that will verify the coupling hub bore is properly geometrically positioned in the hub. It is an easy check and just helps to eliminate possible causes of vibration. 0.002" or less, is great. 0.002" to 0.004" is not very good, anything greater than 0.004" is awful. There are a lot of re-bored imported hubs out there, so the geometric controls on bore location aren't as good as they used to be.

When it comes to couplings we are always here to help.

RE: High vibration during motor solo run

What is the occasion for solo run? i.e. was the motor just refurbished? is there history of recent vibration in coupled condition?


4) Vibration varies from 3.5 to 4.4 mm/sec peak.
I'm going to guess that 2*LF is beating with 2x running speed.


Coupling half restrained with key way.
I'm not sure exactly what you mean there.
What type of coupling and how is it secured to the shaft? (any chance of looseness of hub on shaft in uncoupled condition).

If you're going to do a blue check, they'll obviously do a bearing inspection at that time. I'd suggest also check the shaft/bearing clearance and bearing/housing fit at that time. Also TIR at all accessible locations on the rotor.

Longshot (but firsthand experience) - rotor with mechanically loose bars can look like this. In our case the vib was thermally sensitive... increased over time even during the uncoupled run.

(2B)+(2B)' ?

RE: High vibration during motor solo run

Hmmmm. Still very few of the questions in the 2nd Feb 7 post (mine) have been answered.

Conversion factor from ISO/TC C 12 .
1 picture = 1000 words

Maybe I'll check back later.


Dan T

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