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OLi

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Reply with quote  #1 
Having 2xRPM on the radial on stator frame and rotor and stator just confirmed to be good and circular, why? Refurbed machine, stator built and only new is the stator frame.
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electricpete

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Reply with quote  #2 

I guess this must be a slow speed machine ? (In that case we can rule out 2x = 2LF for 2-pole machine).

One some machines, 2x running speed could lead us to suspect misalignment.

OLi

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Reply with quote  #3 

Yes it is approx 6Hz running speed so it is a hi speed in it's type also highest fall like 300m.

So xducer was on a vetical beam close to the stator isolation proposed to  tight to it but as I belive, what is not bolted and tightened is loose and free. Selection of place from
being nearest to the connection box. So it may not be representative for the stator frame that had a new
fancy design where beam springs took the load from thermal movement during operation and avoiding old
style frictionn based slides or other funny things.
It seems like it created some substantial unbalance since startup 3 months ago that was good. It did run 3 weeks with
higher vibration and trending up. Large clearance was found on lower gen brg. 3 weeks ago and was tightened
and absolute bearing vibration then increased and upper gen brg eddy probe reading "alot" so it was testrun 20% load
and it increased at exciting and further so it was stopped. Most vibration 1xRPM, nice orbits except one position closer to thelower
bearing that could be seen as indication of looseness... So something is loose in the rotor possibly shrink fit rings, maybe.
Bearing vibration near 6mm/s and people normally start to run at 3mm/s as it is so lo freq. and maybe trigger earthquake run for the hills reaction.
So I hold back my gut reaction "lets try to balance to see how it reacts".I was just there to prove that my sensors and convertors was behaving and not the reason for high levels. It was real vibration. Monitoring was giving proper warning. There is a dog buried inside and the tail wagging may create vibrations or "who let the dogs loose" maybe.


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Walt Strong

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Reply with quote  #4 
Olov,

"So it may not be representative for the stator frame that had a new
fancy design where beam springs took the load from thermal movement during operation and avoiding old
style frictionn based slides or other funny things."

Is it possible that a structural natural frequency or least additional flexibility has amplified vibrations?

Walt
OLi

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Reply with quote  #5 
Well, when it was first balanced and started 3 months ago everything was perfectly fine so all I say is met with "It should have been seen at startup" so I happily pass that on. I have not been able to find if the change was sudden or gradually, trying to find that but to start vibratin on HMI was in the famous "0-100%" scale system that is default when nobody understand anything. So they are doing some creep measurements in some funny way to define what is moving next week. It may be that the beam where the radial sensor is are in a resonance area for about 12Hz, 2xRPM and is excited by the looseness multiples from the nearby bearing from the loose ring on the rotor, you never know. I have some data with me back that I will look at that may confirm something like that if I am lucky, or not. So they say it was good when new but I can't say how good it was since the revelation that it is bad and getting worse was in connection with some other investigations regarding a water leak and some bolts breaking in the incoming pipe and being 300 m down in bedrock it is not good having that. So first they believed it was the measurement chain but it is really a machine vibrating out of spec. Eddy probes are in a couple of places mounted near the metal lid radially and the shaft is really short so my 18mm diam probes are not the best as they only see a part of shaft that is maybe 20mm and then a steelplate beneath is not according to the book and they never describe the machine when I ship the sensors. Supplier consultant use 12mm probes and they just as bad. Problem is that they indicate larger movement than bearing clearance but that is uncompensated as neither systems used can do compensation so it is all crap. Absolute bearing vibration is another story they correlate and also indicate very hi levels for such a machine so we all agreed on that it is a bad machine and monitoring had made a indication of that when several alarms were passed so supplier got some work to do. I was thinking about a knocktest on the sensor mount but it was behind a lid in the stator frame and customer didn't like splinters from 2"x4" pine in the stator :-).
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OLi

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Reply with quote  #6 
"Low" speed data indicate a combined run out of like 0.1mm and that is tricky as clearance is around 0.15mm so what can be seen are that absolute bearing vibration is 5-6mm/s and people normally start to run at 3mm/s but this is a hi speed machine like 360RPM and when running up and steady state at low load 20MW vibration increase with time like 0.07 mm in short time in worst eddy probe. Dominating is 1xRPM so there are something moving influencing balancing status possibly both with speed that is ok but also time/temperature that is not good.
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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  #7 

So they opened some bearings and found the fixation pins broken. Would that make a little bearing instability with a funny looking bunny peak? How would you do that
running w/o oil, full load trip that gave some transients including leak in the input tube anything else? Wouldn't there be some squeeak?


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RRS_Dave

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Reply with quote  #8 
Oli,
Is this a vertical hydro machine (I assume it is but you know about assuming). Reason I ask is one of the hydros I monitored was out of line vertically and they broke the bottom bearing pins and ruined the bearing.....twice. (Was that fancy, hard to get wooden bearings) I too saw a big 1x, but this one was only running 150 cpm.
OLi

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Reply with quote  #9 
Yes it is vertical the larger ones mainly are here. Good suggestion thank you. I think it was one of the upper bearings in  this case as the lower is the only the behaves. It is a new refurbed and they discussed loosening the lower bearings and checkhowit hangs but that is some work and they want to run as always. Nowadays that wooden bearing is plastic here when machines are refurbed. Still waterlubed. I had a case some time ago where the mounting of it was less than perfect on a smaller machine and vibration went hi a and weird. A minor adjustment fixed that. We will see today if it is repeat performance like yours. I will tell if I get the information then I learned something.
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OLi

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Reply with quote  #10 
Turbine tripped on a signal from the radial accel on the stator, that actually is placed on a vertical beam. Machine was at low load 20MW and was reducing load when a spike was seen on the HMI 6.24mm/s hi and 11s long and it tripped on that. Later restarting it was again running ok at 20MW with low vibrations, no spikes. So maybe they follow the example RRS_Dave presented or maybe not, time will tell. I don't think a signal that hi and long transient would be a spike from any electrical event, I think it was a mechanical transient but that's me, we will see. No such transient was seen on the other sensors but they are not placed at anything near that radius if it was a torque event.
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Good Vibrations since early 1950's, first patented vibrometer 1956 in the US.
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