Dear All,

Good morning!!

We are looking your valuable feedback why exhaust temperature limited to 529 Deg. C at base load than the previous 561 deg. C??

Background discussion:

UNIT DATE BASE LOAD (Mw) TTRXB TTRXP TTRXS TTXM CPD (Bar) GAS CONS (Sm3) AIR INLET. TEMP
(deg. C)
GT-2A 29-Nov-11 106.1 550 550 551 551 10.3 32926 30
GT-2B 30-Nov-11 103.03 561 562 561 561 9.77 31864 30
GT-2B 16-Apr-12 104.1 529 550 529 529 10.3 32876 27

TTRXB -Speed biased temp. control reference
TTRXP - temperature control CPD reference
TTRXS - temperature control FSR reference
TTXM - Exhaust temperature median corrected by average

If we look the above CPD is 10.3 bar on 16-Apr-2012 compare to 9.77 on 30-Nov-2011, so we were expecting more load.

Moreover inlet air temperature too less 27 deg. C (earlier 30 deg. C)

Here you can notice the major difference in TTRXS (FSR reference temperature control, 561 deg. C for previous base load now 529 deg. C). WHY is it limited to 529 deg. C, what are factors will affect this parameter??

If CPD & ambient are well in control like one of our other Frame-9E (GT-2A) then WHY this unit only produced 104 MW (other unit 106 MW with air inlet 30 Deg. C and same CPD as 10.3 bar).

We are looking your favorable feedback.

 

The unit with low output is using FSR temperature control while the other two units are on CPD temperature control. What fuel are you using? If on liquid fuel do you have a "Heavy Fuel Selection" parameter? if yes, this is what is causing you to go to FSR control. Check your software and see what has selected TTRXS, TTRXP & TTRXS go into a Min. select gate and the output is TTRXB.

 

Dear Johnston,

Thanks for your feedback.

We are having dual fuel selection (liquid / gas) but liquid for only backup. The readings which was provided on natural gas.

GT-2A 29-Nov-11 106.1 550 550 551 551 10.3 32926 30
GT-2B 30-Nov-11 103.03 561 562 561 561 9.77 31864 30

If we look the above readings TTRXB TTRXP TTRXS are nearly same.

But if we look below there is 21 deg.C difference between TTRXB (TTRXS) and TTRXP.
GT-2B 16-Apr-12 104.1 529 550 529 529 10.3 32876 27

We are looking which might have caused for the difference at base load. We'll share if we find any outcome and the meanwhile if anybody having an idea please share with us.

Thanks for your supports.

Take care
G.Rajesh

 

G.Rajesh,

TTRXS = Turbine Temperature Reference Exhaust, Secondary (FSR- or MW-biased exhaust temperature control). So, why didn't you provide the FSR of each machine while operating at Base Load? Hmmmm....

I'm guessing the units use FSR-biased exhaust temperature control as the back-up exhaust temperature control.

So, if that's true, what is the FSR for each of the two machines at Base Load?

What is the actual position of the GCV (from the position indicator/scale on the valve) of each machine at Base Load? (Not LVDT feedback, but actual physical position?)

What is the LVDT feedback from each of the two LVDTs for both machines at Base Load (usually signal name FSGR, and sometimes FSGR_A/FSGR_B for each LVDT, sometimes not--see the IO.ASG file for your machines for the actual names)? (Sometimes it's easiest to use the AutoCalibrate display for this information. There will be nuisance Diag. Alarms annunciated when using AutoCalibrate, but it will NOT affect unit operation or LVDT calibration above 28% TNH.)

When was the last time the GCV LVDTs were "calibrated" for each machine?

From the AutoCalibrate display, what is the amount of servo current for each of the three processors for both machines while operating at Base Load?

What is the gas fuel supply pressure for each machine at Base Load?

What is the P2 pressure for each machine at Base Load?

My guess is the FSR for the unit with lower load will be higher than the FSR for the unit with higher load.

We're not talking about a large difference in load. Two "identical" machines, sitting side-by-side will almost never operate identically. Do the machines use Water- or Steam Inj. for NOx emissions reduction? If so, what is the NOx injection flow-rate for each machine at Base Load?

How long since the last off-line water wash for each machine?

What is the inlet filter differential pressure for each machine at Base Load?

If there is a filter or strainer upstream of the SRV of the machines, what is the differential pressure across the filter/strainer for each machine at Base Load?

Lots of information to be obtained and provided. We need to see ALL of it to be of help--even if you think it might be irrelevant.

There have been other threads on control.com about how sometimes the Control Constants for the two exhaust temperature control curves can be calculated very close to each other, and subsequently the back-up can sometimes unintentionally become active. This is probably likely part of the problem. I'll even go so far as to say the unit operated in TTRXS probably is annunciating a Process Alarm that reads something similar to: 'Back-up Temperature Control Active.' This alarm was added to the myriad of Process Alarms about midway through the period that Mark Vs were produced. Your machines may or may not have this alarm. It was intended to tell a conscious operator that something might be amiss and causing the back-up exh temp control to be active. But, since it doesn't trip the turbine, most operators and their supervisors just ignore it.

Provide all the requested data if you want more help.

 

We are looking your valuable feedback why exhaust temperature limited to 529 Deg. C at base load than the previous 561 deg. C??

Ge Frame 9001E
I Am working on frame 9001E controlled <pre>
alarm help in markv :
-help_QP.DAT process alarms (r;s;t)
-help_BP.DAT process alarms (C)
-help_QD.DAT Diagnostic alarms (r,s,t)
-help_BD.DAT Diagnostic alarms (C)</pre>
can help me
my emeil [email protected]

 

Dear CSA & all,

Thank you for your feedback.

>>So, if that's true, what is the FSR for each of the two machines at Base Load?<pre>
UNIT DATE FSR (%)
GT-2A 29-Nov-11 __________62.88
GT-2B 30-Nov-11 __________60.62
GT-2B 16-Apr-12 __________67.63</pre>
As you guessed unit with lower load with higher FSR (what could be the reason??)

>>What is the actual position of the GCV (from the position indicator/scale on the valve) of each machine at Base Load?

We didn't notice.

>>What is the LVDT feedback from each of the two LVDTs for both machines at Base Load? (FSGR)<pre>
UNIT DATE FSGR (%)
GT-2A 29-Nov-11 _________38
GT-2B 30-Nov-11 _________35
GT-2B 16-Apr-12 _________37</pre>
>>When was the last time the GCV LVDTs were "calibrated" for each machine?<pre>
GT-2A __Nov-2011
GT-2B __Feb-2010</pre>
>>From the AutoCalibrate display, what is the amount of servo current for each of the three processors for both machines while operating at Base Load?

We didn't notice, but we tried to revert the data using historian but it was showing 253% (FAG) for all load.

What is the gas fuel supply pressure for each machine at Base Load?
UNIT DATE FSUP (Bar)<pre>
GT-2A 29-Nov-11 ________23
GT-2B 30-Nov-11 ________24
GT-2B 16-Apr-12 ________22.3</pre>

>>What is the P2 pressure for each machine at Base Load?<pre>
UNIT DATE P2 (Bar)
GT-2A 29-Nov-11 _________17.41
GT-2B 30-Nov-11 _________17.49
GT-2B 16-Apr-12 _________17.54</pre>
>>Do the machines use Water- or Steam Inj. for NOx emissions reduction?

NO

>>How long since the last off-line water wash for each machine?

Both were done last year November

>>What is the inlet filter differential pressure for each machine at Base Load?<pre>
UNIT DATE AIFDP (mmH2O)
GT-2A 29-Nov-11 ___________45
GT-2B 30-Nov-11 ___________50
GT-2B 16-Apr-12 ___________30 (new filters, replaced April 2012)</pre>

>>If there is a filter or strainer upstream of the SRV of the machines, what is the differential pressure across the filter/strainer for each machine at Base Load?

We didn't notice DP at final filter at base load , but normally it is below 0.2 bar. One stariner was installed after the filter, which was inspected and cleaned. (in the past we experianced if strainer chocked, FGUP (upstream of SRV) will be hunting during load variation).

>> I'll even go so far as to say the unit operated in TTRXS probably is annunciating a Process Alarm that reads something similar to: 'Back-up Temperature Control Active.'

the above alarm not included in our Mark V system (Marv V -version B).

Thank you very much for time you spent for our replies.

Take care
G.Rajesh

 

G.Rajesh,

Something is causing the feedback from the GCV LVDT to be higher than the back-up FSR exhaust temperature control curve Control Constants for the conditions at your site.

Why does this happen?

Low gas fuel supply pressure, causing the SRV to be open fully and not maintain P2 pressure setpoint. (This doesn't seem to be happening at your site.)

If there was a restriction in the gas fuel supply (such as a block filter or strainer), it could cause the same condition as above, but the P2 pressure seems okay (based on the data provided).

If there is something causing the mass flow of air through the axial compressor, and turbine, and exhaust to be restricted then this problem could occur--especially if the Control Constants for CPD-biased and FSR-biased exhaust temperature control result in very little differential between the resultant references (TTRXP and TTRXS, respectively).

The inlet filter differential pressure doesn't seem to be excessive, but if the IGV LVDTs aren't properly calibrated, <b>OR</b> the axial compressor isn't clean, <b>OR</b> if the hot gas path components aren't "new and clean" (as in, it's been a long time since a Hot Gas Path Inspection and/or Major Inspection), <b>OR</b> if the exhaust duct back-pressure is higher than normal (usually only occurs in units with an HRSG (Heat Recovery Steam Generator), then the mass flow of air through the machine is restricted.

It could also be that one or more of the compressor bleed valves are leaking resulting a portion of the mass flow of air to be diverted to the gas turbine exhaust.

And, if the calibration of the CPD transmitter(s) isn't accurate this same thing can also occur. The Speedtronic is only as good as it's inputs.

And, if the TTRXP and TTRXS "curves" are very close to each other (which does occur), then this kind of condition can occur.

It's intended for the primary- and back-up exhaust temperature control curves to be relatively close to each other to protect the machine. And, if something is amiss, then unintended back-up exhaust temperature control can "take over" from CPD-biased exhaust temperature control.

Just remember: Gas turbines are basically mass flow machines. More mass flow means more power (at Base Load). Less mass flow means less power (at Base Load). Mass flow is a function of many things.

And, gas turbines are only as good as the gas turbine control system inputs.

 

Thanks CSA,

Yes we agree with you, it could be many reasons. In next HGPI we'll replace hot gas path parts and we'll write you back about the performance.

take care
G.Rajesh

 

And, pray tell, when is the next HGPI?

 

>And, pray tell, when is the next HGPI?

May be in next year between Jan to March.

Take care
G.Rajesh