Calculation process of FSRT in Mark IV

P

Thread Starter

Pirate

What is the formula for FSRT (Temperature Control FSR) in Mark IV? As I know Speed control FSR, FSRN = (TNR-TNH)*FSKRN2 + FSKRN1.

From manual I Found that FSRT = (TTRXB-TTXM)* FSKTG+ ......(the rest part I failed to understand which contains FSKTTC and FSR)

Can anyone help me to find out the rest part?

Another query:
Suppose a turbine is operating at droop control. Due to frequency excursion if it goes to temperature control and stay in temperature control mode for several minutes, will it affect the turbine? Should anyone operate turbine at temperature control mode?
 
While not as user-friendly as the former 'Search' feature, the present 'Search' feature of control.com is very fast and very good.

Entering a search term of "+TTRX" (without the quotes but with the plus sign) yielded the following as one of the top responses:

http://control.com/thread/1242458714#1242663939

Whenever an operator selects Base Load, the unit goes on Exhaust Temperature control. It's actually the most efficient operating mode, and when operating at Base Load the hot gas path parts are subjected to the lowest temperature stresses. That's because Exhaust Temperature Control means that the temperature of the hot combustion gases leaving the first stage nozzle are constant for any given ambient condition, including when frequency decreases.

Of course, when frequency decreases and the unit goes on Exhaust Temperature Control the power output is reduced from rated, however, presuming the CPD feedback is correct, the "firing temperature" (the temperature of the hot combustion gases leaving the first stage nozzle) will remain constant.
 
Dear CSA,

I've gone through all of your links and posts relating to +TTRX and FSRT but I didn't find any established equation of FSRT.

From Manual(of MARK IV) I found
FSRN = (TNR-TNH)*FSKRN2 + FSKRN1

And FSRT = (TTRXB-TTXM)* FSKTG + ......(the rest part I failed to understand which contains FSKTTC and FSR)

I failed to draw that logic diagram in this text box.

Will u please write the rest part of that equation for me?

Or, If anyone know this equation help me to complete the equation of FSRT.

Thank you
 
I've been trying to come up with a response to this question and I don't know exactly how to respond. If you have the Mark IV Speedtronic elementary, it clearly shows the algorithm for determining FSRT, so I'm not really clear what the problem is.

EXCEPT that one needs to remember that when the unit is operating on CPD-biased exhaust temperature control the Speedtronic is trying to put as much fuel as possible into the turbine without exceeding the exhaust temperature reference (limit) defined by TTRX.

So, if that means that FSR has to be 45.4% for the "median" exhaust temperature, TTXM, to equal the exhaust temperature reference (limit), TTRX, then FSRT will be equal to 45.4%. And, if that means that FSR has to be 85.7% for the TTXM to be equal to TTRX then FSRT will be equal to 85.7%.

The calibration of the fuel valve LVDTs (presuming there are LVDTs on the fuel valve; or the fuel flow feedback in the case of Liquid Fuel) has a lot to do with the "final" FSRT, only because the Speedtronic will adjust the fuel valve to whatever position is required to make TTXM equal to TTRX.

If you're trying to equate FSRT to some load and have that relationship be true for all operating conditions on any turbine (such as for two Frame 6s on the same site running on the same fuel), it's not a proper way to compare operation. There is a general "rule" that says that FSR should be 'approximately between' (note the wide range!) 60% and 80% for a new and clean turbine burning the primary fuel with a properly tuned and calibrated fuel delivery system under rated ambient conditions (temperature, site elevation, atmospheric pressure, and exhaust back-pressure). The typical Base Load FSR value for a new and clean turbine burning natural gas or liquid fuel operating at rated conditions with a properly tuned and calibrated control system is about 70-75%.

The above are just guidelines, and every turbine is slightly different. Even two units on the same site installed and started up at the same time can behave very differently over the years.

And a lot of turbines, especially older units, have lots of performance degradation and calibration/tuning problems, AND they run at ambient conditions which are far different than nameplate rating.

As the unit is loaded from FSNL to Base Load, TTRX will decrease. As TTRX decreases, FSRT will decrease. I will try to find a Mark IV elementary and see if I can glean something from the FSRT algorithm, but it would be very helpful if we understood what you are trying to prove or disprove.

But, in any case, remember: FSR will be whatever it needs to be when Base Load is selected to make TTXM equal to TTRX.

If you have some condition that you are trying to troubleshoot or explain, perhaps if you told us we could provide more information. In thinking about this problem, I've never given FSRT much thought in the past. Because, FSRT will be whatever it needs to be to make TTRX equal to TTXM.

Having said that, if FSR (FSRT) is only 33% or is 97% I would be looking at possible causes, but I wouldn't be suspecting the calculation of FSRT. I would likely have a look at the Control Constants you mentioned to be sure they are the values listed in the Control Specification. But the problem would most likely be caused by something else, such as improperly calibrated LVDTs, or a dirty compressor, or a poorly calibrated 96CD-1 transducer, or something like that. I've even seen some pretty strange droop settings cause some very odd FSRs.
 
This concept of CPD-biased exhaust temperature control is very generic to GE-design heavy duty gas turbines, so even though the control systems have changed over the years the concepts of turbine control haven't. The same exhaust T/C arrangements are used in gas turbines and the same practice of monitoring compressor discharge pressure is used, and has been since the earliest heavy duty gas turbines were produced in the 1950s.

So, basically this same algorithm has been used by GE in their digital control systems since the early 1980s in the Mark IV (SIMPLEX or TMR), the Mark V, the Mark VI, and is still used today in Mark VIe (SIMPLEX or TMR). The only difference is the number of exhaust T/Cs that are used on the various turbines, and the type of control system (SIMPLEX or TMR), and in some cases the number of CPD transmitters.
 
Dear CSA, sorry something I don't get in the quote.

>As the unit is loaded from FSNL to Base Load, TTRX will
>decrease. As TTRX decreases, FSRT will decrease. I will try
>to find a Mark IV elementary and see if I can glean
>something from the FSRT algorithm, but it would be very
>helpful if we understood what you are trying to prove or
>disprove.

Isn't TTRX supposed to be equal "The Isothermal Limit" during part load. So it should be constant during loading until reaching Base Load? Please explain.
 
C
CSA,

During transition from speed droop to base load, how the CSRGV will vary?

Can u explain briefly?
 
Aptx4869,

You are correct, TTRX is "constant" until it hits the "knee"--the point at which TTRX starts to decrease as CPD/CPR increases. But, fuel control is a function of FSRT, which is derived from TTRX.

Watch the FSR Display on the HMI as the unit is loading. FSRT will start out at 100%, and as the unit loads up it will start decreasing as FSRN increases. When FSRN exceeds FSRT (or when FSRT is less than FSRN) the unit will be at Base Load, CPR/CPD-biased exhaust temperature control--TTXM will be equal to TTRX, and the IGVs will be a maximum operating angle.

REMEMBER--the majority of the different FSRs (FSRSU (FSR Start-up); FSRSD (FSR Shutdown); FSRACC (FSR Acceleration Control); FSRN (Speed Control FSR); FSRT (Temperature Control FSR); etc.) feed into a MINimum SELect block--and the LOWEST input value becomes the the output to the fuel control system. When the unit is operating you should see that FSRSU is 100% (out of the way of Speed Control and Temperature Control and Acceleration Control), and so is FSRSD. FSRACC is usually just slightly higher than the FSR that's in control (FSRN or FSRT) during loaded operation. FSRMIN (Minimum FSR) is just a "floor" (lower limit) for FSR under any circumstances and does not feed into the MINSEL block function.

You could also use the extremely useful and helpful Trend Recorder function of Toolbox/ToolboxST to capture data during a start-up and loading to verify this on a graph which can be printed and referred to often (instead of watching real-time data on a CIMPLICITY display and trying to remember what happened when). Trend Recorder is an EXCELLENT tool that is not utilized nearly as often as it should be.

Hope this helps!
 
Chiranjeevi,

CSRGV is the output of a MINimum SELect block/function in the application code. There are several different IGV references which all feed into the MINSEL block, and the lowest of the inputs becomes the the reference to the IGVs.

At the point when the control transitions from Droop Speed Control to CPR/CPD-biased Exhaust Temperature Control, the IGVs must be at maximum operating angle. The definition of Base Load is when the IGVs are at maximum operating angle, <b>AND</b> the actual exhaust temperature is equal to the exhaust temperature reference.

Many DLN combustor-equipped machines operate with TTXM very close to TTRX at mid- to upper loads--this is because the IGVs are used to control air flow through the machine to prevent blowing-out the diffusion flame in the machine. DLN combustors operate with very lean fuel/air mixtures and the only "knob" to control air flow is the IGVs. BUT the IGVs can be closed below the point at which the exhaust temperature exceeds TTRX, so mid- to upper load often occurs with TTXM very close to TTRX--but when the IGVs are NOT at maximum operating angle.

Only when the IGVs are at maximum operating angle AND TTXM equals TTRX is the unit on exhaust temperature control.

Hope this helps!
 
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