Problem with high X2 appears before synchronization and after it there are no significant changes. This is an old turbine from 1964. This turbine was ge-neral overhaul but problem with X2 appeared after generator failure. The generator and the rotor of generator were repaired. We've had suspicion that was loose clutch. The clutch on the shaft had been changed but the high value of X2 is still.
I hope you understand my English. I'll try write something more on Monday. I'll be very grateful for any suggestions.
Based on the 2X bode plot it looks like a structural resonance frequency excited by 2X running speed.
I assume that you do not have proximity probe data... Would be nice to see what the shaft is actually doing.
Since there have been repairs made, I would suggest looking for soft foot in the generator mounting. Improper supporting may have caused this. Loosen one hold down bolt at a time and check to see if the foot lifts, and if the 2X changes.
I would also look at alignment issues, the 2x resonance may have always been there, but only becomes apparent now that you have a 2X forcing function due to misalignment or due to improper coupling up of the machine. I assume it is a flange style coupling. Did your mechanics record runouts on the coupling? Did they have any problems coupling it up? Were the fits ok?
"Why don't you knock it off with them negative waves? Why don't you dig how beautiful it is out here? Why don't you say something righteous and hopeful for a change?" Oddball, "Kelly's Heros" 1970
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the bearing supports being in a pedistal on concrete look like a solid design.
I assume the gen is to the left. the bearing and its suporting rings look like it could be possible to have undesired excessive clearance and thus the bearing be loose. But I don't think that would be a problem by itself, just make the problem greater.
I don't understand all I see between the bearings. Is this the "clutch"? (I have never worked on unit with a clutch)
You called it clutch, but is it an direct drive engagement device (or does it allow shaft slippage). I'm going to assume it is like a splined hub that meshes with geared couplings on each shaft.
If that case, the alignment between the gen's two bearing supports and the turbine's two bearing suport would be my first suspecion for the problem. I would not have a recomended acceptable bearing line, like say, the 4 bearings being in a straight line. It might require the outboard gen bearing higher to make a "fair face" alignment between the gen and turbine due to rotor sags.
Also, how hot is the turbine casing, is it radiating heat into the turbine side bearing causing a rise and thus that bearing need to be set low at cold. I don't really see that as a large problem though.
Now with older units, I have been biten where the original bearing alignment from design didnot work, a change was made during first years of operation, but not documented. then 40 years latter, it is "discovered" the machine needs to be realigned and the original problem comes back.
Quick war story...I was setting up controls on older machine just rebuilt by others. During return roll up, SEVERE oil whip. Not knowing what happen during rebuild, I recomended in meeting bearing needed to be raised by at least 0.015". I didn't realize overhauling engineer had made big deal out of finding that bearing high and had "fixed it" as extra work
Ok, this generator is built like its bigger cousins... I assume that orbit is off shaft probes...
If the 2x suddenly showed up on synchronization would say that this is related to the generator rotor. That 2X in the probe trace is too symetric to be due to preload or misalignment and looks almost electrical.
Since it is not logically electrical and the recorded runouts are higher than I would have expected and show a pattern that could generate a 2X. I would suggest refitting the coupling first of all, as that is the easiest thing to check.
It could also be a shaft crack, so wath the 2X amplitude and phase for any changes if you continue running..
"Why don't you knock it off with them negative waves? Why don't you dig how beautiful it is out here? Why don't you say something righteous and hopeful for a change?" Oddball, "Kelly's Heros" 1970
Please see FAQ731-376 for tips on how to make the best use of the Eng-Tips Forums.
Ive seen Maag and SSS clutches used to disconnect the turbine and allow the generator to remain connected, and used to correct system VAr's.
Put units into Canada particularly, where there were long overhead lines.
If so, is there a slight alignment problem, that gives a vibration in different engagements of the clutch?
I think that the MAAG clutch was hydraulically actuated - that looks like one on the photo (I have never seen one though!)
The SSS clutch is self shifting (Hence SS) and operates like a bicycle free wheel, so as the turbine slows, the clutch disconnects at synchronous speed (hence the final S)
"Why don't you knock it off with them negative waves? Why don't you dig how beautiful it is out here? Why don't you say something righteous and hopeful for a change?" Oddball, "Kelly's Heros" 1970
Please see FAQ731-376 for tips on how to make the best use of the Eng-Tips Forums.
