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GE Gas Turbine IGV angle
What is the logic? GTG is not operating in Temperature Control mode.

Frame 6 Machine with Mark-V. IGV is operating at 57 DGA with TTXM=562 degree C. The IGV moves to 62 DGA and is operating between 59-62DGA. What is the logic. GTG is not operating in Temperature Control mode

3 out of 4 members thought this post was helpful...

BND,
There is 'exhaust temperature control' and there is 'exhaust temperature control.' Which exhaust temperature control are you referring to?

Most GE-design heavy duty gas turbines have CPD-biased exhaust temperature control (this is what defines Base Load--and is the maximum allowable exhaust temperature based on operating conditions when the IGVs are at their maximum operating angle.

And, most GE-design heavy duty gas turbines also have IGV exhaust temperature control--which is the method of maximizing exhaust temperature at part load (below Base Load) by keeping the IGVs closed as long as possible which restricts the air flow through the machine and increases the exhaust temperature.

When the unit is being loaded from synchronization and IGV exhaust temperature control is enabled and active the IGVs will be held closed until TTXM (the average exhaust temperature) gets very close to TTRX (the CPD-biased exhaust temperature control reference--again: the maximum allowable exhaust temperature for the current operating condition). So, the IGVs will be held at 57 DGA until TTXM gets very close to TTRX (sometimes, depending on the vintage of the control algorithm, it will be when TTXM equals TTRX) as load is increased the exhaust temperature would tend to increase above TTRX--and the IGVs are opened slightly to maintain the TTXM/TTRX relationship. This is IGV exhaust temperature control.

This continues during loading until the IGVs are fully open, and when TTXM equals TTRX then the unit is said to be operating on CPD-biased exhaust temperature control. Again, CPD-biased exhaust temperature control only occurs when the IGVs are fully open--that's part of the definition of Base Load: when the IGVs are fully open and fuel flow is such that TTXM equals TTRX.

Hope this helps!

Two last things. First, if the turbine you are working on has DLN (Dry Low NOx) combustors, IGV exhaust temperature control is not operator-selectable; it's always on.

Second, when a GE-design heavy duty gas turbine without DLN combustors is operating with IGV exhaust temperature control disabled and not active when the exhaust temperature hits 700 or 900 deg F (sorry; I can't remember which temperature exactly) the IGVs will start opening to maintain that temperature (either 700 or 900 deg F) as the unit is loaded until such time as the IGVs are fully open. The operator interface display will show "EXHAUST TEMPERATURE CONTROL" during this period. The purpose of this 'exhaust temperature control' is to limit combustor pressure pulsations during loading (which occurs around 700 or 900 deg F--which I could remember which, but I can't; sorry). So, really, there's 'exhaust temperature control' and there's 'exhaust temperature control' and there's 'exhaust temperature control.' (Isn't this fun?)

CSA

I posted it in wrong thread.

As both of IGVs and FSR (right?) have ability to regulate exhaust temperature,how to make sure when the IGVs are not at maximum operating angle,the exhaust temperature is controlled by IGVs exhaust temperature control not CPD-biased exhaust temperature control?

Best regards
Neo

1 out of 1 members thought this post was helpful...

Neo,

The IGV position reference, CSRGV, is the output of a MAX select block--just like FSR is the output of a MAX select block.

The IGV temperature control reference is basically the same as the CPD-biased exhaust temperature control reference. (Some older units had a 5-10 deg F offset, making the IGV exhaust temp control reference slightly lower. Newer units don't have that offset.)

The reason that CPD-biased exhaust temperature control is used as the IGV exhaust temperature control reference is that it makes life simpler: The CPD-biased exhaust temperature control reference is being calculated all the time, and it does represent the maximum allowable exhaust temperature control reference, so using it as the IGV exhaust temp control reference makes sense.

I don't have access to any Mark VI application code at the moment, but I think the IGV exhaust temp control reference is called CSRGVX or something like that. When operating on IGV exhaust temp control the IGVs are modulated (positioned) based on comparing the actual exhaust temperature (TTXM) to the CPD-biased exhaust temp control reference (TTRX) and either opened or closed to make TTXM equal to TTRX. A lot like how CPD-biased exhaust temperature control positions the GCV--when the IGVs are full open. Again, that's how the Speedtronic knows when it's supposed to be on CPD-biased exhaust temperature control (Base Load)--when the IGVs are full open (at their maximum operating angle).

Does this help? IGV exhaust temp control uses the CPD-biased exhaust temp control reference (TTRX) as it's reference for positioning the IGVs when IGV exhaust temp control is active and enabled.

Have a look at how CSRGV is determined, and you will find lots of new questions.

CSA,

Thank you again for your comment, it helps a lot.

So when the unit is on Base Load, the exhaust temperature is controlled by CPD-biased exhaust temperature? and when the unit is on Part Load,it is controlled by IGV exhaust control?

I heard that when it is a Combined cycle, IGV exhaust control is meant to keep T4* at maximum value, and if it is a simple cycle, the exhaust temperature is not controlled.

When closing the IGVs on Part load to keep to the T4* at maximum, how does the CPR change, and CPR in turn will decide the maximum allowable exhaust temperature. That seems tricky.

I would like to refer to CSRGV when time is available.

Best regards
Neo

1 out of 1 members thought this post was helpful...

Neo,

What's this "T4*"?

We can talk about CSRGV; later. Once we finish with L4T! Which should be VERY interesting for the unit at your site.

There's no trickery involved. At Part Load (less than Base Load) the IGVs can be used to maximize exhaust temperature--and the maximum allowable exhaust temperature at ANY time is always TTRX. So, the IGVs just remain at minimum operating angle until TTXM reaches TTRX. As fuel increases and TTXM would tend to increase the IGVs open to keep TTXM equal to TTRX.

Once the IGVs reach maximum operating angle and TTXM equals TTRX--well, that's the definition of Base Load. It's very simple, and, again, no trickery involved.

Units without a heat recovery steam generator (an HRSG, or "boiler") on the gas turbine exhaust (or units with a diverter in the exhaust, which can divert the exhaust directly to atmosphere instead of to the HRSG) can operate without IGV exhaust temperature control (if they are non-DLN units). This is commonly called "simple cycle" (sometimes called "single cycle") and is more efficient than operating with IGV exhaust temp control ON because the unit is exhausting to atmosphere and there's no benefit in making exhaust temperature higher by restricting air flow through the unit. (The benefit of maximizing exhaust temperature is for the overall combined cycle--when steam is being produced with the gas turbine exhaust. It actually slightly reduces the efficiency of the gas turbine (the simple cycle), but it increases the overall thermal efficiency of the plant (the combined cycle)).

Neo,

sorry I have a question may be related to this discussion. GE gas turbine frame 6B old upgraded to Mark V, at start up the temperature control starting at 40% speed, and the speed going up very slow up to 47% and held for 2 seconds then going down,the IGV angle in control from 34 to 86. so please can you help me to overcome the early starting of temperature control.

thanks
Sameh Salama

Saneh

I think when you referring to temperature control it is IGV temperature control,right?

I checked CSRGVPS and CSRGVV3 blocks in the application code,i find that when the unit is under 40% rated speed, CSRGV is specified by CSRGVPS (Part speed VIGV refrence). So the unit should not in IGV temperature control mode. CSRGV is the output of a minimum selector out of IGV temperature control, IGV part speed control and maximum open IGV position (usually 86deg.)

During start up,the IGV will normally open from 34deg (My unit),and reaches the minimum operating angle 57deg (My unit) when the unit ramped up to 85.72% corrected speed (My unit). And i think the IGV temperature control will not take in charge before the unit ramped to 100% corrected speed. And the IGV temperature control is not the same for combined cycle unit or simple cycle unit.

Above is the the background knowledge i know about IGV control.

---------------------------------------------------------------------------------------------------
You may should check the history data of TTXM,CSRGVPS,CSRGVX,TTGXGV and any other signal that is related to IGV control to see whether there is any unusual.
---------------------------------------------------------------------------------------------------

And i think the best way for you is to offer more information (combine cycle or simple cycle...), and ask CSA for help, as he is the real master.

Hope it helps.

Best regards!
Neo

3 out of 3 members thought this post was helpful...

Neo,

Here are the kind of questions one should ask after a careful reading of the original post:

When was the control system upgraded to Mark V?

When did this problem start? After a maintenance outage? After a trip from load?

What Process Alarms are active during starting?

What Diagnostic Alarms are active during starting?

[Most people simply ignore all alarms--that's because some Speedtronic turbine control panels were so poorly commissioned that they are continually--and erroneously--annunciating lots of alarms, and operators just become immune to them. Also, some site do so little maintenance and up-keep that alarms come and go, and some stay for years. Alarms are important--VERY important--and while most "operators" never have it properly explained to them it's one of their most important job functions: to manage alarms. Managing alarms means to take action whenever an alarm occurs. First, they should silence any audible alarm indication; then they should read the alarm text message and acknowledge the alarm. Then they need to take action to resolve the alarm--which is not just to check to see if the turbine has tripped, and if it's still running, to just walk away. Resolving alarms means understanding what the alarm message is indicating, taking action to see if the alarm message is true (such as checking the L.O. Header Temperature to see if the High L.O. Temperature alarm is true or not), and if it is true take appropriate action to lower the L.O. temperature--or notify the appropriate department/individual to take action, while continuing to monitor the condition and lower load if the L.O. temperature can't be lowered.

Diagnostic Alarms are NOT nuisance alarms--they weren't intended to be, but that's how most people perceive them. A lot of times it's found that during an investigation of a serious forced outage that one or two Process Alarms had been active for some time indicating a failure of some sensor or device that prevented operators from properly recognizing a serious condition as it was developing. Just because a turbine continues to run when an alarm (Process or Diagnostic) is annunciated does NOT mean the turbine is running as it should.

So, always try to remember to ask, "What alarms were annunciated?" (Here at control.com the overwhelming majority of questioners never respond to the request to list alarms, probably because there is no printed record of alarms (the printer is either broken, out of paper, or unplugged). And, operators don't log alarms to the Operations Log as they should. But, people should still be made aware that alarms are important and they should not be ignored (that's one of our duties--to try to help people be better operators and technicians).]

What fuel is being burned during starting?

Next, you explain what should be happening versus what is being described, following with some details of a normal, typical start-up.

While it's not uncommon for units to hit CPD-biased exhaust temperature control briefly during acceleration--it's NOT common for them to hit exhaust temperature control at 40% speed. The usual cause of a problem like this is that the starting means is not supplying sufficient torque during starting to accelerate the machine so the Speedtronic is adding additional fuel to try to help acceleration.

The IGVs, if they are modulated type, should not move from the "closed" position (typically 34 degrees angle) to the minimum operating position (usually 57 degrees angle) until, as Neo says, about 80% speed--regardless of exhaust temperature. It seems like some logic is being forced or some Control Constant has incorrectly been modified that is causing the IGVs to open prematurely--which also has the effect of increasing the air flow through the axial compressor which usually increases the torque required from the starting means, which is not helping the problem at all.

If the machine is older, and the starting means and/or the torque converter have not been refurbished in a while it's very likely that insufficient torque is being transmitted to assist with acceleration, causing more fuel to be admitted, causing the exhaust temperature to be very high (prematurely).

A lot of sites have been steadily increasing start-up and acceleration FSRs over time to compensate for degrading starting means and/or torque converters. The starting means, through the torque converter, should be providing torque up to about 50-60% speed for a properly working starting means system. At that point, usually the turbine speed is greater than the starting means/torque converter output speed and the clutch opens, and usually fuel increases slightly to help maintain acceleration. Because the IGVs are still closed (or should be!) the exhaust temperature is still increasing as speed is increasing. Usually, exhaust temperature peaks just about the time the IGVs should be moving from 34 to 57 degrees. And then the exhaust temperature should generally reach it's maximum peak--which can never by higher than the CPD-biased exhaust temperature reference, TTRX, sometimes hitting the CPD-biased exhaust temperature control (TTRX) but the unit should still be accelerating. Exhaust temperature will usually start dropping around the time the IGVs move to 57 DGA, and CPD will also start increasing faster.

But, the torque assist from the starting means (via the torque converter) is very important--especially at lower turbine speeds during acceleration. Without it, so much fuel would be required that the fuel would be limited by CPD-biased exhaust temperature control (FSRT will be less than FSRACC or FSRN or FSRSU)--and the acceleration rate (TNHA) would slow, and if it starts decelerating then the unit will trip on "bog down."

If the turbine has a diesel engine starting means, I've seen dirty air filters and dirty fuel filters cause low torque output. If there is any white smoke coming from the diesel engine exhaust that means there is incomplete combustion in one or more cylinders--which means that fuel is being waster and torque production is lower than it should be. Black smoke is good--but if it's excessive black smoke then the diesel starting means is overloaded. If the diesel was recently serviced, it's not uncommon for the fuel control racks to be improperly adjusted. Have you checked the diesel speed to see if it's at it's normal speed during acceleration? (The signal name is usually PN, PN_RPM or PN_PR, or something similar.)

If the torque converter was recently refurbished, there have been several incidences of poor quality refurbishment recently. There can be problems with any solenoid(s) in the torque converter oil circuit, as well as oil flow problems in the torque converter oil circuit (sometimes there are strainers which need periodic maintenance; sometimes there are manual valves which need to be checked to make sure they are in their correct positions).

Then you ask the questioner to please write back to let us know how they resolve the problem.

0 out of 1 members thought this post was helpful...

CSV, In response to the following excerpts from your post below:
>
"[Most people simply ignore all alarms--that's because some
>Speedtronic turbine control panels were so poorly
>commissioned that they are continually--and
>erroneously--annunciating lots of alarms, and operators just
>become immune to them... Alarms are important--VERY important--and
>while most "operators" never have it properly explained to
>them it's one of their most important job functions: to
>manage alarms. Managing alarms means to take action whenever
>an alarm occurs. First, they should silence any audible
>alarm indication; then they should read the alarm text
>message and acknowledge the alarm. Then they need to take
>action to resolve the alarm--which is not just to check to
>see if the turbine has tripped, and if it's still running,
>to just walk away. Resolving alarms means understanding what
>the alarm message is indicating, taking action to see if the
>alarm message is true (such as checking the L.O. Header
>Temperature to see if the High L.O. Temperature alarm is
>true or not), and if it is true take appropriate action to
>lower the L.O. temperature--or notify the appropriate
>department/individual to take action, while continuing to
>monitor the condition and lower load if the L.O. temperature
>can't be lowered.
>
>Diagnostic Alarms are NOT nuisance alarms--they weren't
>intended to be, but that's how most people perceive them. A
>lot of times it's found that during an investigation of a
>serious forced outage that one or two Process Alarms had
>been active for some time indicating a failure of some
>sensor or device that prevented operators from properly
>recognizing a serious condition as it was developing. Just
>because a turbine continues to run when an alarm (Process or
>Diagnostic) is annunciated does NOT mean the turbine is
>running as it should.
... (that's one of
>our duties--to try to help people be better operators and
>technicians)..."

You have painted with a very broad brush the skill-set and qualifications of the Operations Department in Gas Turbine based power plants.

I come to this site because it usually presents very useful information, although I read many questions from Engineers that seem so obvious.

You are a very qualified, educated, and properly trained person, from your responses concerning GE Gas Turbines.

Perhaps what you should have said is "Some operators aren't aware of how serious some of these alarms are" or "There are instances where...", instead of insulting the highly skilled operators at gas turbine plants, many who have come through the Navy Nuclear Program or higher level university programs on power plant operations.

This site has been quite helpful to some of our folks, and I would hate to be banned for defending my operators. Your technical advice, on the whole, is quite useful, but please refrain from painting all operators as a bunch of helpless, uneducated, unskilled and unmotivated personnel who need help in determining how to respond to an alarm.

Kind Regards

1 out of 1 members thought this post was helpful...

TomasEduardo,

Your statement, "...although I read many questions from Engineers that seem so obvious...." is very telling and reveals you have not experienced the wide disparity in operations which exists even in the Americas, and to a larger extent around the world.

With the exception of some EU countries (and those soon to be exiting the EU) training requirements for power plant operators (gas turbine-based or otherwise) are very low, and getting lower. Power plant owners and supervisors falsely believe automation will protect the plant from every possible problem or failure--even operator-initiated problems.

You, sir, are leading a charmed life, and working with ex-Navy nuke personnel who MUST be capable of understanding the work of their posting and rely on their shipmates to keep everyone alive when at sea, and have LOTS of training before they step aboard a ship or sub, means the level of thought and critical thinking in the Control Room-and probably in the plant--is very high. You should count your lucky stars, while at the same realizing that your situation is the exception rather than the rule.

I specifically said "most people" not all, recognizing that there are very qualified people in the industry--but they are the exception rather than the rule. I also want to say that in most cases the fault lies not with the operator or technician, but with the people hiring them. Most hiring managers (not all) are not willing to pay for training, worried that after receiving the training the employees will leave for a higher wage somewhere else--across the street, in some cases.

There is a saying about a CFO (Chief Financial Officer) asking his CEO (Chief Executive Officer) about the risk of investing in training their employees only to have them leave. The CEO replies, "What if we don't invest in training, and the employess stay?" That's not (yet) the prevailing way of thinking in the ivory tower, or below.

I hope you and your operators will continue to return to control.com--but I more sincerely hope you and your operators will offer the benefit of your experience and knowledge to others posting here. For my part, I will reduce the editorializing and generalizations. Sometimes after struggling with people to try to get them to look at P&IDs and alarms to understand what happened to their plant and how it happened--only to be told, "YOU JUST MAKE DAMN SURE IT WON'T HAPPEN AGAIN!" (by modifying the control system programming) my frustration boils over to my responses.

But the fact remains, your experience and current situation is the exception--not the rule; I sincerely hope you never land in a lesser situation. And please accept my sincere apology if you or your operators felt tainted by my broad brush (which comes from painful personal experience). Believe me when I tell you that the audible alarm annunciator (beeper; bell; horn; etc.) in most Control Rooms is totally disabled (in some cases broken from excessive use) and operators don't pay any attention to any alarms when they are annunciated, and mostly only when the unit trips.

In many cases their supervisors actually tell them the control system will protect the unit and they shouldn't take any action to reduce load or shut down without first obtaining the permission of the Plant Manager (who's always got both eyes on the spreadsheet). And then gets extremely angry when "the control system" doesn't do what he thinks it should, and there's a wreck.

Again, my apologies for not considering there are good operators in the world. I only wish I ran into more of them, more often.

By Sameh Salama on 12 July, 2014 - 4:16 am
0 out of 1 members thought this post was helpful...

Neo

thanks a lot for your valuable reply, my unit is simple cycle. to overcome my problem issue (unit can't reach the FSNL) I increased the IGV angle from 34 to 42 from the beginning then the unit reaching the FSNL successfully. on the other hand with the existing IGV angle 34 the unit can't reaching the FSNL, so please advice.

Best regards
Sameh Salama

Sameh Salama:

It is my honor that you think my response helps.

I advise to read CSA's response carefully. i am sure it helps.
If it still doesn't work, let us work together then.

BTW, in my opinion, you should not set IGV manually during start. it may cause damage.

Best regards
Neo

Sameh Salama:

How is everything going?

Did you solve the thermal blockage problem by increasing the start means torque?

Best regards
Neo

0 out of 1 members thought this post was helpful...

Neo,

Already i checked the diesel engine loaded speed which was 2320 rpm and replace the torque converter by refurbished one and the inside pressure reached 120 psi as the old one pressure was 58 psi. still the same problem (after starting the turbine exhaust temperature coming very high in short time (20% speed temp 140C, 40% speed 500C) as the temperature control starting from 40% of speed. furthermore i remove the fuel nozzles and cleaned.

for your kind information this problem not found before the last MI since 5 months ago.

I need to share with some control snap shots

thanks a lot for your always support.

Sameh Salama

Sameh Salama:

Glad to receive your reply.But this is out of my capability, lets ask CSA for help.

And your problem seems complicated. If it is not caused by lack of torque produced by startmeans, will it be the fuel system isn't calibrated properly? Or the control constant is not set properly in FSRSU block. It really confuses me.

I hope CSA will give guidance.

Best regards!
Neo

CSA,

Already i checked the diesel engine loaded speed which was 2320 rpm and replace the torque converter by refurbished one and the inside pressure reached 120 psi as the old one pressure was 58 psi. still the same problem (after starting the turbine exhaust temperature coming very high in short time (20% speed temp 140C, 40% speed 500C) as the temperature control starting from 40% of speed. furthermore i remove the fuel nozzles and cleaned.

for your kind information this problem not found before the last MI since 5 months ago.

I need to share with some control snap shots.

By Chiranjeevi on 15 May, 2017 - 10:39 am

Does the final block of CSRGV is min select block or max select block of above stated variables?

By sardar99 on 16 May, 2017 - 3:21 am
0 out of 1 members thought this post was helpful...

Hi,

>The IGV position reference, CSRGV, is the output of a MAX
>select block--just like FSR is the output of a MAX select
>block.

I think. FSR is output of minimum select gate, and at 700 Degree FTTXM IGV starts opening if IGV temp selected "ON".

Thanks