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OLi

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Reply with quote  #16 
Well home again, jobs done from 50 to 22 microns in 1 run using data from previous testing and a helpful stable motor. No resonance to be seen by eye, run-up flat as a pancake. So it only took 3-4 years and the final 5 trips to the site. Balancing/weight move cycle is on average 2 days (no jack oil, OH crane used for rotating... )but this time it was actually done in 1 day but a bit long. No more fiddling or adjusting to improve it can not be accessed further unless anything is acting up. Unusual was (maybe not for this motor it behaved previously) but generally, we put static weights both end the same and all 4 sensors went nicely towards the center. Sometimes you are lucky when you need it. Why it would need trim balancing after sitting 3 years on the dock side beside the Atlantic, well your guess is as good as mine. Why the other one that is "identical" didn't need it, answer would be the same, I have not a clue.
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Dan Timberlake

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Reply with quote  #17 
"motor feet 6-8pcs are fitted in a milled recess in the steel plate," - Sure sounds like an unfortunate installation problem of base plate thicker than the drawing or positioned too high.
OLi

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Reply with quote  #18 
Yes I also think so, you don't "adjust" the compressor pipes 1m diameter and 200 Bar, they fill all space under the machine.
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OLi

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Reply with quote  #19 

So I get back again to the coast of the atlantic. I did think it was done since there was no news for some time. Now it is all connected and running tests at full power and vibration 1xRPM goes up to about the same as before we added 2x230 gram but still in the same angle so in priciple it would be fine adding another 2x230 grams but the track is full so I try to make them turn the coupling 180 DEG so I will know what end of it is bad this time, GBX or motor. Drive end is the worse end. What would a GBX be balanced to, grade 6.3 or better? input speed like 1800RPM and output 4.5x faster, 38MW motor power. I wonder if there are something else giving problem that looks like that. I wonder if hooking up using a soft coupling could change center of rotation. I would not think it would be expected. It looks like the other string behaves better, I have not seen any data from that yet and that is also strange, they should be as similar as you can make them. Unless the foundation differ that is.

I have some Bently FFT that looks like half finished they contain both "negative" and pos frequencies, why do they look like that? Specific one is very differnt other sides of 0 does that say something? I only seen things like that during developement. Do you use it like that if you use Bently/GE data? It is also waterfall so it does look funny to me.


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vogel

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Reply with quote  #20 
Hi Oli,

That is a full spectrum, positive frequency components account for precession in the same sense as the shaft rotation (forward precession) while negative components represent negative precession.

The most common causes for increased negative precession are bearing anisotropy and rubs. Huge negative precession is usually due to wiring issues (X and Y probes exchanged).

All Bently software can show spectral data as a Full or Half spectrum. Other software can too.

I'm not sure about this, but I think that I read in the other forum that Bill Foiles showed this tool to Don Bently back in the old days.

https://zone.ni.com/reference/en-XX/help/372416H-01/svtconcepts/guid-164b18c9-97ad-41ff-a921-f74d40d7f63d/

OLi

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Reply with quote  #21 
Thank you, followed the link and now again confused on a higher level but quite interesting. I have not looked so close at the Bently world and special features before. So yes the bad behavior of one of the machines may include some touching and subsequent bending. Since I will try to reduce initial vibration from unbalance I hope it will stop that behavior too or I will have to try to find where it happens. It will now have run a couple of days after the initial 6h surge test that I have data from so it may have worn down if it is light touch. I think they would have yelled higher in the phone if it had gone the other possible way, a serious rub and trip. Time will tell when I get some more data to look at.
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OLi

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Reply with quote  #22 
I am in a pickle here. I balanced one of the motors a month ago and testing did proceed and it run fine but the other "identical" was giving trouble and it was decided to also balance that and now upon arrival to site again both misbehave, flat orbits hi levels etc. Similar oilpressure. temp, bearingtemp etc. Vibration goes up when starting like 90 microns and then reduce to 20 microns in 2.5 hours full speed full power. I got a oil particle count as rub is suspected and they are NAS5 and NAS6 that is maybe not so many particles. Vectors are all over the place, roughly 180 degree off compared to when I left them a month ago and up to 5 times higher. So further balancing seems unlikely right now. So there must be a reason for the behavior, it also seem to relate to temp diff in windings...
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Walt Strong

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Reply with quote  #23 
"Vibration goes up when starting like 90 microns and then reduce to 20 microns in 2.5 hours full speed full power." This would be like a reverse thermal bow, where rotor shape gets straight with heat. Somewhat unusual!

 "Vectors are all over the place, roughly 180 degree off compared to when I left them a month ago and up to 5 times higher." This would indicate possible loose parts on rotor; such as cooling fan or rotor bars. Any indication of rotor electrical fault? Broken shaft? Loose of cracked shaft coupling? I just worked on a 14000-hp BFP with crack coupling that was giving unbalance indication!

It might be worthwhile to inspect rotor-stator gap and possibly use a fiberscope to inspect for rubbing.

Walt
OLi

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Reply with quote  #24 
Yes we will do a inspection Monday. Worst unit was tested by a involuntary slight bump or drop test going here that made the shaft height from floor 4.7mm lower and was factory repaired, nothing indicating what was done, just what was suggested by OEM, doing ok during balancing solo run, strange it was required being direct from factory albeit it was standing on the doc of the bay with a tarp for 2 years after factory repair.... A quick ocular inspection yesterday indicate that it is a lot of crudd just outside and near seal that is from corrosion protection of the shaft that never was cleaned out. So we hope to find the seal full of that stuff, then we have a reason for the behavior. Yesterday one started out good, ended bad, the other being the other way around that is better, worst case we need to balance so they are more the same, just the vectors cooperate and stay stable. We have a type of diaphragm coupling, would you know if they are sensitive to the direction of storage for say 3 years?
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Walt Strong

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Reply with quote  #25 
I do not believe that corrosion protection material in the seal would cause the unusual vibrations particularly with the phase shift. Perhaps this same material was put on the shaft journal inside the bearings, and that could cause pretty strange vibrations because an actual will film is not present. I would recommend rolling out at least one bearing and inspecting it. The diaphragm coupling has a flexible steel disk that I would not expect to be affected by storage for three years.

Walt
OLi

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Reply with quote  #26 
Thank you. Yesterday both units behaved the same, starting hi, ending low. We will inspect today.
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Good Vibrations since early 1950's, first patented vibrometer 1956 in the US.
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OLi

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Reply with quote  #27 
1+mm "scratch" found in shaft in seal, no balancing until fixed and then it may not be required. I guess, so going home.
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Good Vibrations since early 1950's, first patented vibrometer 1956 in the US.
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