Critical speed

Hi everybody
I would be grateful if anyone could tell me how are critical speeds in ge F5 5100 rpm gas turbine.?
If I recall correctly one of them was about 2800 rpm.?!

There are GE-design Frame 5 heavy duty gas turbines. And there are GE-design Frame 5 heavy duty gas turbines.

Some are single shaft; some are two-shaft.

Most ALL HP shafts are rated at 5100 RPM (5094 to be exact, but that's another whole entire thread unto itself). BUT not all.

Some have more axial compressor stages than others; some less axial compressor stages than others.

Some have variable IGVs; some have Bang-Bang IGVs (open or closed with no possible in-between position(s)).

Some have variable second-stage nozzles; some don't.

There are just a LOT of variables and intangibles we don't know about the machine(s) you are asking about. GE doesn't usually publish critical speeds (there's several reasons, one of which is they don't give humans any control over the speed range from FIRE speed to FSNL (when the unit is firing) so as not to allow the unit to get hung or stopped at or very near a critical--MUCH better than publishing a number and NOT preventing people from "accidentally" stopping/parking a unit at or near the published critical speed (which has happened on more than one occasion). People just want to play (believe me when I say that!!!), so they take away the ability to play and the potential problem goes away. Magic! Even if you publish the critical speeds and tell people in big, bold letters in multiple places NOT to stop within 300 RPM of them--they will.

You want to know what the criticals are for your machine? Get some vibration monitoring equipment (better than the seismic (velocity) pick-ups that GE uses to protect the machine (because they're not really good for much other than protecting the machine, and they're only adequate for that purpose) and start the unit and plot the vibration. Even on a well-balanced machine it's pretty obvious where the critical speeds are--for the turbine.

For single-shaft machines there is also the load/reduction gear (which has its critical speed), and the generator shaft, which also has its critical speed(s). And, there are different varieties of both--load/reduction gears and generators--which can also have an impact on "machine" criticals.

We're all here, brother. We just don't have enough information to be able to help. And, the only entity who does is: GE, or possibly the packager of the GE-design Frame 5 heavy duty gas turbine.

Finally, over nearly four decades, I have read some texts and reference books which pretty well "predict" what the critical speeds are for particular high-speed rotating pieces of equipment. (No; I don't recall the names at this writing. I just had time on many start-ups to look at documents I found on many sites (after asking permission--which I was too often denied.... another long story for another entirely different thread) and was quite often pleasantly surprised at what I found and read.

You asked a question--and it seems no one had the answer, and/or maybe some people just needed more information than you posted. As difficult as it is to believe for MANY people (yourself included, it seems): Not every GE-design Frame 5 heavy duty gas turbine is the same as every other GE-design Frame 5 heavy duty gas turbine. Yes, they all suck and squeeze and burn and blow, but then so does every other GE-design Frame heavy duty gas turbine.

And that's a fact, Jack.