SRV doesn't work

Z

Thread Starter

Zihni

Dear Experts..

I work in a CCPP which have two F9E and MS9001 GTs. We have a problem related to operation SRV valve in our GT. GTs work under Mark V control. Can you please help us?

During few days We had a problem in GT. There was fluctuation in P2 gas pressure. It had changed from 19 to 20.8 bar. But We were still in the work. We haven't stopped GT.However last night while load decreased from the GT, Load and gas pressure suddenly started too much fluctuation in GT (from 17 to 24 bar. We stopped load decreased and then We increased to BASE LOAD. We saw that SRV full opened and P2 pressure 24.4 bar (this pressure is gas station output pressure). It still works GT and P2 pressure stable but 24.4 bar. After from GCV, gas pressure is 15.8 bar.
SRV current value is;<pre>
FPRGOUT : 20.15 bar FPRG_INT : -100.00 %
FSGR : 104.9 % FPRG_CNV : -100.00 %
FAGR : 88.42 %
FPG2 : 24.41 bar</pre>
What may be problem in SRV? How to can be repaired? Thank you for your help..
 
Hi,

We too experienced such problem in the past.

It might be a servo valve problem or line filter choke.

In our case it solved after replaced servo valve.

You can try to clean the servo valve filter and see the improvement.

best of luck
G.Rajesh
 
If the SRV is fully open, indicates that the servo is damaged or the card who feeds the servo is damage. The SRV controls the turbine speed, so If the turbine is still on service when you try to stop it, at the moment 52G opens the turbine will increase the speed and it is possible that its trip for overspeed. So take precautions

regards,
Voyager2
 
Voyager2,

The SRV does NOT control turbine speed. The SRV controls P2 (intervalve) pressure as a function of turbine speed. This, in turn, maintains a fairly constant pressure drop across the GCV.
 
otised,

I'm trying to understand when the pressure drop across the GCV is or would be constant. As the machine speed increases during start-up, the SRV opens as a function of speed to increase the P2 (intervalve) pressure ahead of the GCV. And, the GCV actually doesn't ever open very much above the firing/warm-up value (because as the pressure upstream of the GCV increases the flow through the GCV increases even as the GCV stays in a very small range of opening).

During acceleration during start-up the P2 pressure increases (as turbine speed increases) and the pressure downstream of the GCV also increases--even if the GCV doesn't move at all during starting, or moves very little. So, it would seem that the pressure drop across the GCV would be changing, though slowly and not by much, during acceleration.

Once the unit reaches rated speed, the P2 pressure reference is now "fixed" because if the unit is being operated in parallel with other generators and their prime movers on a properly controlled grid and the grid frequency is relatively stable the P2 pressure reference is stable--meaning the SRV should be controlling a "constant" P2 pressure regardless of the position (opening) of the GCV.

As the GCV opens to increase fuel flow to the turbine when it is being loaded the P2 pressure would tend to start to decrease--BUT the SRV senses the decrease in P2 pressure and opens the SRV to maintain the actual P2 pressure equal to the P2 pressure reference.

As the GCV opens, the pressure downstream of the GCV will increase. Even with a constant upstream pressure (when the unit is at rated speed), the pressure drop across the GCV will not be constant as the unit is loaded an unloaded.

So, I'm a little confused about the "constant pressure drop" statement. Do you mean that when the GCV upstream pressure remains constant as the GCV opens and closes during loading (when the turbine speed should be 100%) that the flow through the GCV is more directly proportional to the stroke (opening) of the GCV than it would be if the upstream pressure were allowed to fluctuate with supply pressure?

I'm just trying to understand if I've not been thinking about this correctly or in this manner.

Thanks!
 
CSA,

I did say "fairly" constant. That is also probably not accurate - I forgot to consider the impact of the IGV position on compressor discharge pressure. And, with DLN systems, there are different flow paths as the combustion mode changes. But my basic thought process was that once synchronized, P2 would be held constant by the SRV, and with full open IGV's, compressor discharge pressure would be fairly constant, and hence the pressure in the combustors would also be fairly constant, the differential pressure across the GCV would also be pretty constant.

P2 - Pcomb = dP_GCV + dP_fuel nozzles + dP_piping
Anyway, I agree that for combined cycle and DLN applications, the GCV dP won't be constant.
 
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