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Batman

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Hello!

I don't wish to interfere with the other discussion regarding the "background vibration of adjacent machine" but this topic reminded me of something.

I will soon start monitoring lube oil pumps on GTs. For each GT, there are three identical pumps located next to each other on each tank. Two pumps out of three at any one time are in operation.

Are there tips or what to do or not to do for monitoring these pumps. Being so close together I'm presuming there will be an influence on the vibration of one from the other and thinking about it I may see varying values for the same pump depending whether the very next pump is in service or not. We all know how important it is to capture data at 'fixed' or same conditions so if pumps in service alternate then would I expect different values for different conditions? The ideal would be to take readings of each pump at the same operating scenario but this may be difficult to schedule in practice . 

Are my concerns justified?

Any suggestions?
RGf

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Are you sure that both of your LO pumps will be inservice together? Most CTs I'm familiar with have 2 AC pumps, 1 INS, 1 backup; 1 Emergency AC and 1 Emergency DC and I haven't seen the 2 "normal" pumps running together.



MarkL

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I've been in a CCGT station today and will be again tomorrow and I am pretty sure both theyre units(Plant 1 and Plant 2) are on same set up as RGF outlines, two Ac units on top of the tank, with one running at any time and a backup DC unit.
That said I have felt transferred vibe through the idle one sometimes as they are within 3-4 feet of each other.


In the case of the station I visit, we work it this way-
On day one, I collect all primary pumps (A Units) also the cooling towers and the ACC fans. When I'm finished collecting I tell the control room guys and they switch over to the backup units at the end of the shift and will continue to run them for 30 days. I will collect the readings from the (B Units) units tomorrow. That's pretty much how we have always done that plant, I have only measured the DC Motors and the fuel Oil back up pumps once a year.
Batman

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pdf GT Lube Oil System.pdf         

Hello,

Thanks for the replies, however the system operates as I described. Two pumps in, one pump standby. See attached extract from the GT Manual.

Any suggestions on the initial concerns.

Thank you.
Batman

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It seems this method of operation is not common by the feedback to my question.[wink]
MarkL

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Reply with quote  #6 
Hi Batman, I do do Plants in he same campus for this particular company and they run on the duty or standby running setup with 1 Ac unit for each, they are about 50hp each in the 450mw plant and 90hp each on the 560mw unit.
Then each has 1 Dc unit each unsure of the power rating.
RustyCas

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Reply with quote  #7 
I would expect the typical concern for pumps like this would just be bearings. While identification of “bearing defect frequencies” is usually ‘sold’ (by instrument mfgs), trending of overall acceleration usually gives a better result. With my CSI system I do this with a parameter which looks at Maximum Peak Acceleration. Acceleration is highly attenuated with distance, so one pump is unlikely to influence the other (when looking at acceleration).

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RBT

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Eleven days late on my reply.I also monitor these pumps and motors at our 3 on 1 combined cycle. Some suggestions I would give are as follows;1. Bearings will be the main issue, but not in the motors.Usually the loud noise you hear outside the skid is the pump top inboard bearing, they will roar, especially if cocked. The best place to monitor these bearings is axial right beside the bearing. 2.Couplings will be the next issue, strobe the Couplings for issues.Look for the coupling to have dropped down. If there is an A/C-D/C lube oil piggyback motors attached vertically you will have several problems with these (DC motors- brushes),they have two couplings. It seems these are more prone to coupling issues. If you have the A/C-DC piggybacks, I know the "C" face is suppose to be in alignment, but sometimes they are not. While the coupling covers are off check the alignment, it is very tight spaces. They can be out of alignment, it will then eat your DC brushes, affect couplings,bearings etc...

The control room might be able to shutdown one pump for a few minutes of data collection.
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