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Dan Timberlake

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Reply with quote  #1 
We  just received a preliminary "vibration" report from the fan supplier's field service specialist for a new center mounted 850 HP ID fan during cold commissioning.  Sleeve bearings.  The fan and motor are mounted on a nicely crafted steel base in turn mounted on steel spring isolators. The Vibration was measured with accelerometers mounted the bearing casings.  I have submitted questions, starting with whether the "vibration" is filtered or unfiltered, and requested accompanying spectra/FFts etc.

In the meantime, the fact the attached axial "readings" (whatever they are) are so high they have caught my attention.

Before some meat and potatoes arrive, Does anyone have any comments or suggestions ?

thanks,

Dan T

Attached Images
png Axial readings high .png (75.46 KB, 45 views)
jpeg 20170407_140214.jpg (79.93 KB, 40 views)

spciesla

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Reply with quote  #2 
The highest reading is ~1.5 mm/s rms.  Assuming that it is all running speed (sinusoidal) that doesn't seem "high".  Plots needed.
Shoveldr

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Reply with quote  #3 
I don't consider those levels high at all, 0.06 in/sec is pretty smooth, I wouldn't worry about ratios at those levels.

Walt Strong

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Reply with quote  #4 
Dan,

I agree that the vibration levels are quite low, even the axial direction. About all you can judge from this type of test is the original factory rotor balance. I would expect that a fan of this size would be rigidly mounted to a substantial foundation, so vibrations could be expected to change. I expect that the shop test was run with cold air and low flow, and possibly with the dampers closed. ID fans run with hot air of about 300°F, so the air (gas) density is lower than with cold shop air. Rotor unbalance can change after the initial or several operating cycles with hot air, so trim balancing in the field may be required. Of course you know all this, so I'm preaching to the rest of the choir!
Walt
Dan Timberlake

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Posts: 116
Reply with quote  #5 
Thanks for the replies.

I've requested spectra, and even if the values are filtered or overall.
So far, Nuttin' .

The busted VFD will be repaired next week, and  cold commissioning will continue, if only with vibration info from  the plant's DCS.

The cold commissioning  tests were run with the fan completely installed at the plant. Damper status unknown. 

By design the fan and motor are mounted on a nicely crafted continuous steel base in turn "mounted" on  a small legion of steel spring isolators.  "Mounted" = just resting on the isolators, reportedly bolted at the four corner isolators only.   Kind of curious design situation for a location of seismic activity 2B.  http://www.nishkian.com/nishcore/wp-content/uploads/2014/01/U.S.-Seismic-Zones-Map.jpg

Again, thanks to all.

Dan T

Attached Images
png pic for vibe board .png (931.00 KB, 41 views)

Walt Strong

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Reply with quote  #6 
Dan,

I have worked in the power sector a long time, and I have never seen a foundation quite like this. My guess is that the intent of this design is to allow variable speed operation without resonance issues. As you know there are 6 degrees of freedom (3-lateral and 3-rotational) and not just vertical-lateral, so it is still possible to get resonant amplification (for example in axial/thrust direction) at a specific rotor speed. The base still needs seismic failsafe restraint that should be non-contact bumpers. Make sure no one tried to bolt the base at the corners. Have fun with your testing and evaluation!

Walt
Dan Timberlake

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Posts: 116
Reply with quote  #7 
Hi Walt, 

Here is an isolation mounted 960 HP FGR fan supplied by another  German company  for a similar project a couple of years back.  I have to double check, but I  // think // it is constant speed.
The twin I-beam section between the fan bearing pedestals is Model T wimpy in my opinion, and the fan housing is expected to obediently slide axially gently and accurately when growing thermally with questionable guidance.



cajun ga for vibe board.PNG 

The measurements and inspections  I'd hoped to make, or have made, were "overcome by events," but my theory is along the lines before sliding the expanding fan housing jacks and twists the ODE fan bearing out of alignment, causing a sudden and severe bearing rub.

Attached Images
png cajun ode snap vibe for vibe board.PNG (37.73 KB, 12 views)

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