I've gone back to the original post and looked over the original questions:

>At 92% THL the GT goes to exhaust temperature control.
>Usually at this period of year (cold weather) the GT reaches
>easily the 98%TNL.

>My questions: Are GCV fluctuations the reason that the GT
>Control goes under exhaust temperature earlier than
>usual?? How match the GCV fluctuation tolerance should be?

TTRXP is the Primary (CPD-biased) Exhaust Temperature Control Reference. TTRXS is the Secondary (Back-up; usually FSR- or MW-biased, but since this is a two-shaft mechanical drive it's probably FSR-biased). TTRXB is the speed signal-biased lower of TTRXP or TTRXS; from the data provided there is no bias, and TTRXB is equal to TTRXP. Finally, TTRX is the Exhaust Temperature Control Reference--the speed-biased lower of TTRXP or TTRXS; TTRX is the limiting factor in fuel flow.

From the data provided, the actual exhaust temperature, TTXM, is approximately 50 degrees below TTRX--which is equal to TTRXP, the CPD-biased exhaust temperature control reference. So, my question is: What makes the original poster think the unit is on "exhaust temperature control"?

The definition of exhaust temperature control ("Base Load") is the IGVs are at maximum operating angle and the actual exhaust temperature (TTXM) is equal to the exhaust temperature reference (the speed-biased lower value of TTRXP or TTRXS). From the data provided, the IGVs are "open" (I'm not precisely sure what the maximum operating IGV angle for a MS5002C is, but it's probably 84- or 86 DGA, or somewhere thereabouts--the Control Constant name is usually CSKGVMAX), but the exhaust temperature is still 50 deg C less than the exhaust temperature reference--so the unit isn't technically on exhaust temperature control-

<b><i>UNLESS</i> the unit is operating on IGV (Exhaust) Temperature Control</b>--which as was said earlier, kind of goes along with how the IGVs are moving to try to maintain a constant exhaust temperature....

To answer bkarim55's original question: No; GCV fluctuations cannot generally cause a unit to reach exhaust temperature control prematurely--unless the unit is operating very near TTRXS (meaning, TTXM is very close to TTRXS--and TTRXS is less (lower than) TTRXP). And, that's not happening, based on the information provided. TTRXS is slightly higher than TTRXP (which is as it should be).

So: <i><b>What makes you, bkarim55, believe the unit is operating on exhaust temperature control?</b></i> The Status Field of the HMI might say "EXH TEMP CONTROL" when the unit is operating on IGV (Exhaust) Temperature Control, but that's NOT the same as CPD- or FSR-biased Exhaust Temperature Control. (Isn't GE wonderful like this?)

bkarim55, does the unit exhaust into an HRSG or some kind of regenerator or something similar, where it would be advantageous to have a high exhaust temperature? If so, does the Mark V have buttons for selecting "IGV Temp Control ON" and IGV Temp Control OFF"? If so, is the "IGV Temp Control ON" active? This would mean the IGVs were being used to maximize exhaust temperature, but I don't think that would result in a Status Field message of "EXH TEMP CONTROL" unless TTXM were equal to TTRX--and per the data provided, it's not.

What makes someone think the unit is operating on exhaust temperature control when TTXM is 50 deg less than TTRX?

As was said early on, it would seem there are two problems (at least!). One, a mildly fluctuating GCV, and two, a perception the unit is prematurely operating on exhaust temperature control.

I think we're chasing ghosts on this GCV fluctuation thing. Isn't the real question: Why is the unit "prematurely" on "exhaust temperature control"?

Waiting for answers and information.

 

1. check the mA in three controller to servo valve.

2. Check the hydraulic oil supply line thoroughly for any choking.

3. check whether hydraulic oil supply pressure is constant or not.

4. clean properly the fuel servo valve (I to p converter) and its pre-filter (last chance filter).

 

Dear responders;

Thank you so much for sharing your knowledge and experience..

<b>Deep Dive RCA</b> you are right respected CSA! It's never easy to do an online RCA especially if it's a forum. Yes! Forums and World Wide Web consume time and you may find nothing <b>but</b> it's never frustrating because at the end you are learning many many things linked to your concern. I think I already was <b>lucky</b> when I discovered Control.com and its wonderful little search box on the right side of each webpage and I'm very VERY lucky to chat and share knowledge with people like the honorable CSA.

IGVs are <b>not</b> controlled by exhaust temperature. IGVs are just full open at 100%TNH

<i><b>> What makes you, bkarim55, believe the unit is operating on exhaust temperature control? </b></i>

Excuse me CSA I think there is a little confusion between the post of November, 7th and the one of December,15th (see below).
November was hotter (25°C ambient temperature) than December (about 8°C when I used View1 to record data). This is why when using view1, TTXM was far away from TTXR
<pre>
<b>Post of November, 7th</b>
GCV 68 73%
P2 (Inter-valve pressure) 12,74 13,40 bars
SRV 46,75 47,96%
FSR 67,70 73,74%
Nozzles AG 1,9 2,1 DGA
TTXM 521 524 °C (the control is switching between Speed and Exhaust temperature)


<b>Post of December, 15th</b>
Time FRS TNH TNL CSGV TTXM FSRN FSRT TTRXP TTRXS TTRXB TTRX FAG FSG
01:45 70.90 99.74 92.70 83.4 477 70.41 82.75 521 530 521 521 -6.12 69.84
01:46 72.31 99.72 92.62 84.5 476 72.25 84.34 520 527 520 520 -4.14 71.32
</pre>
Usually this Frame 5 reaches easily 98%TNL at 25°C ambient temperature and the original question was about the relationship between GCV instability and Exhaust temperature Control ?

Too many questions (over fifteen I numbered) dear CSA and I'm on leave for two more weeks.. As soon as on site I answer your questions

Regards
Karim

 

Dear All;

<b>Yesterday, something happened!</b>

There was gas detection at the turbine compartment (gas leak due to a bad gasket) so it was decided to stop the machine for couple hours to fix the damaged gasket. During the startup, it was observed that the GCV doesn't close completely, still <b>open about 10%</b>. So it was decided to extend the shutdown time to replace both MOOG and the no working LVDT.

But even with brand new genuine MOOG and LVDTs, the GCV opening is still the same "about 10%".

Without spare SRV/GCV valve on site and because the SVR valve is working correctly (it closes), the GT started and she is running now with the same GCV fluctuation (as before replacing MOOG and LVDT).

What could stick the GCV valve to close? Are there any risks when running with defect GCV?

Regards
Karim