island mode operation in a combined cycle...when?

Hi guys

Our plant is a combined cycle with DLN2.6+ Mark VI , the electric configuration its as shown (9FA GAS TURBINE)
my questions are:
what is necessary to happen to get in a island mode?
island mode is when there is a external failure and the turbine is disconnected (52G open) to the grid and keeps running in FSNL?


Another question related to other things ...if the unit in a start up keeps feeding the auxiliary equipment by the start up transformer (SUT) what could happen if I reach base load ? I mean if the operator forget to make the switch from the start up to the auxiliary transformer (we do that in 40 mw in GT)
both transformer are 9/12 MVA.
why do I need an auxiliary transformer...its only to not have to "purchase" energy form the grid?
Can I even reach based load with the SUT?
best regard

RATM
electric.png
 
Hi guys

Our plant is a combined cycle with DLN2.6+ Mark VI , the electric configuration its as shown (9FA GAS TURBINE)
my questions are:
what is necessary to happen to get in a island mode?
island mode is when there is a external failure and the turbine is disconnected (52G open) to the grid and keeps running in FSNL?


Another question related to other things ...if the unit in a start up keeps feeding the auxiliary equipment by the start up transformer (SUT) what could happen if I reach base load ? I mean if the operator forget to make the switch from the start up to the auxiliary transformer (we do that in 40 mw in GT)
both transformer are 9/12 MVA.
why do I need an auxiliary transformer...its only to not have to "purchase" energy form the grid?
Can I even reach based load with the SUT?
best regard

RATM
View attachment 436
Hello All
Ratm,

After have read your post,I think that you should have a better overall control concepts of your plant.

For example you defining island mode like:
"Island mode is when there is a external failure and the turbine is disconnected (52G open) to the grid and keeps running in FSNL? "
I can see how misunderstanding of island mode can be !

It is clear that one should understand that :

Island mode is not necessary when grid faults occur , this event can be called "load rejection", or Tripping by Line/Grid protections, or other Generator/Gas turbine controller protection operating/tripping .

First Is there any kind of utility "connected/supllied " with/by your plant ,,, ( if this is the case)

For example you can have smelter /ciment factory, paper mills, process steam .....

This is the case when you are in island mode!

I think that there is a confusion between "house load" & "Island mode" Which are differents modes.

We do not see all the auxiliary equipments and drawing is like cutted but no matter .

I will review the provided SLD and write some comments after that.

How you operating /starting the plant/gas turbine ?
I mean how LCI is supplied by START UP TRF,?? Auxilliary TRF,?

Hope this can help,
ControlsGuy25.
 
hi controlsguy thanks for your response
"I think that you should have a better overall control concepts of your plant."...for sure that why i am asking here to the experts
let me describe briefly our situation:
we have a combined cycle power plant 9FA gas turbine with DLN 2.6+,(GT 220 mw, steam turbine 110 mw) we are connected to the national grid by request of the dispatch centre, most of the time we are in base load, sometimes (always by the requirements of the dispatch centre) we operate in partial load
"First Is there any kind of utility "connected/supllied " with/by your plant" NO we do not have that, we only feed the national grid
as you say island mode is when the unit is feeding a factory (for example) and you are NOT connected to the grid, again we do not do that.
the start up process is something like this:
we are connected to the national grid in 110 KV and we are feeding our auxiliary equipment by the start up transformer
110/6,6kv from here we feed the isolation transformer wich feed the LCI 6,6/2,2kv then the unit start to accelerate ..and you know the rest.
by the time we have 40-45 MW in the gas turbine, the operator make the switch between the start up to the auxiliary transformer..
so the auxiliary of the plant is now being feed by the auxiliary transformer or like you said HOUSE LOAD mode
and then we reach base load or partial load conected to the grid (feeding it)
in the past we have suffer many trips, and many blackouts but i never have seen a island operation in this unit (but I KNOW that several years ago the unit has operating in island mode because of a failure ......i dont know the details

so what have to happen to go into a island mode?

Another question related to other things ...if the unit in a start up keeps feeding the auxiliary equipment by the start up transformer (SUT) what could happen if I reach base load ? I mean if the operator forget to make the switch from the start up to the auxiliary transformer (we do that in 40 mw in GT)
both transformer are 9/12 MVA.
why do I need an auxiliary transformer...its only to not have to "purchase" energy form the grid?
Can I even reach based load with the SUT?
best regard
 
hi controlsguy thanks for your response
"I think that you should have a better overall control concepts of your plant."...for sure that why i am asking here to the experts
let me describe briefly our situation:
we have a combined cycle power plant 9FA gas turbine with DLN 2.6+,(GT 220 mw, steam turbine 110 mw) we are connected to the national grid by request of the dispatch centre, most of the time we are in base load, sometimes (always by the requirements of the dispatch centre) we operate in partial load
"First Is there any kind of utility "connected/supllied " with/by your plant" NO we do not have that, we only feed the national grid
as you say island mode is when the unit is feeding a factory (for example) and you are NOT connected to the grid, again we do not do that.
the start up process is something like this:
we are connected to the national grid in 110 KV and we are feeding our auxiliary equipment by the start up transformer
110/6,6kv from here we feed the isolation transformer wich feed the LCI 6,6/2,2kv then the unit start to accelerate ..and you know the rest.
by the time we have 40-45 MW in the gas turbine, the operator make the switch between the start up to the auxiliary transformer..
so the auxiliary of the plant is now being feed by the auxiliary transformer or like you said HOUSE LOAD mode
and then we reach base load or partial load conected to the grid (feeding it)
in the past we have suffer many trips, and many blackouts but i never have seen a island operation in this unit (but I KNOW that several years ago the unit has operating in island mode because of a failure ......i dont know the details

so what have to happen to go into a island mode?

Another question related to other things ...if the unit in a start up keeps feeding the auxiliary equipment by the start up transformer (SUT) what could happen if I reach base load ? I mean if the operator forget to make the switch from the start up to the auxiliary transformer (we do that in 40 mw in GT)
both transformer are 9/12 MVA.
why do I need an auxiliary transformer...its only to not have to "purchase" energy form the grid?
Can I even reach based load with the SUT?
best regard
Hi Ratm,

Thank you for such feedback.

Well I was pretty sure about how unit (GT ) Been operated /started from SLD provided.

I will try to get some answers/comments on your last questions :

You asked what will happen to go into a island mode?
Again I would say that it is rather an "house load " than island mode, ( without be able to see the overall SLD i cannot say more that about island mode at your site).

if the unit in a start up keeps feeding the auxiliary equipment by the start up transformer (SUT) what could happen if I reach base load ? I mean if the operator forget to make the switch from the start up to the auxiliary transformer (we do that in 40 mw in GT)
both transformer are 9/12 MVA.
why do I need an auxiliary transformer...its only to not have to "purchase" energy form the grid?
Can I even reach based load with the SUT?

Did you think about in case that a sudden grid failure or even STG failure /tripping???

In case you loose SUT there will be UAT available for feeding the various "house-load " or "plant load " I think.

What can be the scenario in such case ,,? In case SUT power supply lost /failure .., ?

Do you have electrical systems study ? If so can you tell us the developped scenario/Operations in such event?

Again I dont have access, to the systems studies in your plant, that can be interesting to check that.

Last but not least, you asking if you can reach base load with SUT,,?

My opinion is to check with what OEM specify on such case, there surely be the answers there.

This is all about protections selectivity and power systems sudies that engineering designed such SLD .

In my opinion I would not reach base load with SUT.

Your OEM O&M manuals, have the right answers on these questions.

Me think that Engineers who designed this SLD, took into account differents possibles scenarios of the operations of the plant , and you should clearly try to track/Follow the OEM recommandations .

Is your plant designed by Belfort (GEEPE)?? That can be the case here .
I know very well how GE Belfort study and design their equipments/systems in power generation.

Please write us back, what is your opinion about these comments,

Hope this can help,

ControlsGuy25.
 
ratm,

I think you have some concepts a little mixed up. But, let's try to get at what appears to be your main question--based on the subject of this thread you started.

If your plant is connected to a grid utility with a load larger than the capacity of your plant then the plant can produce Base Load--by accepting load from the grid/utility. (And, the grid utility has to "make room" for the load from your plant by reducing the load(s) on other plant(s) in order to keep the frequency stable and at rated.)

If your plant is NOT connected to a grid/utility, and it is NOT supplying a process plant (such as a refinery or a cement plant or a fertilizer plant or a chemical plant, etc.), the ONLY load the plant can produce while maintaining a stable frequency is the load connected to the generator(s) through the 52G generator breaker(s) (I'm referring to the gas- and steam turbine generator breakers). If that's the start-up transformer or the unit auxiliary transformer, then the loads on those transformers are the only loads being supplied (with the exception of the excitation equipment). If that's 11 MW total, then the gas- and steam turbines can only supply 11 MW at 50 Hz. If they try to supply more megawatts, they can't--the load is only 11 MW. BUT, what happens is as the operator tries to increase the load the frequency will go up. If the operator tries to reduce the load below 11 MW what will happen is that the frequency will go down. Unless the operator does something to change the load on the SUT or UAT or excitation transformers (the "hotel load"), the load will not change. And, the load on the turbine-generators will not change. No amount of extra fuel or steam will increase the load on the generators--unless someone does something to change the loads on the SUT or UAT or excitation transformers (the "hotel load") nothing is going to change the MW output of the generators (total). You will probably be able to change the individual loads on the two generators, so if the GT was putting out 7 MW and the ST was putting out 4 MW, if you increase the fuel to the GT the load on the GT will go up, and at the same time the load on the ST will go down. Once the load on the ST reaches zero MW and the load on the GT reaches 11 MW any increase in the fuel to the GT will cause the frequency to increase--BUT NOT THE LOAD ON THE GT. Full stop. Period.

It's NOT possible to go into island mode unless there is load OTHER THAN the SUT and UAT and excitation transformers (the "hotel load"). Island mode is ONLY possible if there is load connected to the turbine-generators in addition to the SUT and UAT and the excitation transformers (the "hotel load").

I think you may be asking about Isochronous Speed Control mode--see, Isochronous sounds like "island," but it's not. Isochronous Speed Control mode is the governor mode (the governor is the part of the control system that controls the unit speed)--and since frequency and speed are DIRECTLY related, it can also control frequency.

See, when a synchronous generator is powering a load independent of other generators something--or someone--has to control the speed of the unit in order to control the frequency of the load being supplied. Now, the control system's governor function can do that automatically, or the operator can do it. And, if the load is going up or down the operator will be very busy adjusting the fuel to keep the speed--and frequency--stable. OR, the operator can select Isochronous Speed Control Mode. Isochronous Speed Control Mode can automatically detect when the load is changing--because when the load changes the speed (and frequency) changes, and so Isochronous Speed Control mode will automatically adjust the fuel to maintain the desired speed (and frequency). Automatically.

When two synchronous generators are synchronized together and supplying a load independent of a grid or other generators, ONE--and ONLY ONE--of the prime mover turbine control systems can be in Isochronous Speed Control mode (unless there is some kind of Isochronous load sharing scheme--and I'm NOT talking about that, or any kind of "external" "Master Load Control" or PMS (Power Management System); if you bring up one similar that's in operation at your site now in this thread, I'm done with it (this thread)). And, the operations department DOES NOT control the load on the Isochronous Speed Control unit!!! Full Stop. Period. They do it with the other generator, who's control system governor is going to be operating in Droop Speed Control.

There have been TENS of threads on Control.com over the last couple of decades about Droop Speed Control--so many that at times it seems like the name of the site should have been changed to DroopSpeedControl.com. If you want more information about Droop (and Isochronous Speed Control) use the 'Search' feature of Control.com.

If this isn't what you were asking about (isochronous mode operation in a combined cycle power plant...when?), then you have to be more clear. Island mode implies supplying more than just the plant "hotel load." However, Isochronous Speed Control Mode can also be used to control frequency of the turbine-generator(s) when supplying the "hotel load." But, the plant control systems have to be configured to allow this. So, this may be what you're asking about--using Isochronous Speed Control mode to maintain "hotel load" when separated from the grid/utility. But, in NO CASE can the output of the generator(s) in the power plant produce more load than the "hotel load" of the plant if it's not supplying loads other than the "hotel load."

Simple as that. (It's an overly simplified explanation, but it seems to fit.) AGAIN, if there's any kind of external load control system for the plant when it operates independent of the grid/utility, my contribution to this thread is over. It changes things too much. And there's too much that you would have to be able to tell us to know what might be happening. And, that's just not going to happen. It never does. The thread just dies. After a lot of people have put a lot of effort into it.

It would help if you would clarify what it is you are asking about.

Usually, large combined cycle plants have very detailed Operations Manuals, many of which have written descriptions of the design criteria for the plant--including operations like supplying the "hotel load" independent of a grid/utility, if it's even possible.
 
ratm,

When you read and study the Droop Speed Control threads you will discover that turbine-generator speed (and frequency) when synchronized to a grid with many other generators and their prime movers is controlled by the grid frequency--because generators synchronized to a grid MUST all run at the same frequency. They MUST.

So, when a turbine-generator is synchronized to a grid with other generators and their prime movers the governor function of the prime mover control systems--operating in Droop Speed Control aren't really controlling prime movers speed (generator frequency). The grid is. (That's why it's called "Droop Speed Control”--the actual speed (frequency is less than the speed reference and because we know that's okay we make use of the difference between the reference and the actual to control the energy flowing into the prime movers, which changes the electrical amperes coming out of the generator (which changes the watts, kWatts, MW).

But, when not synchronized to a grid with other prime movers and generators the governor function of the prime movers control system has to be adjusted to maintain the desired frequency. And while that can be done by trained, knowledgeable and experienced operators, they would prefer it to be automatically done (so as not to interrupt their newspaper reading or their mid-shift biryani). And Isochronous Speed Control mode is the automatic method to do that (maintain frequency)--not ”island mode.”

Once you clarify what you're asking about (without introducing any talk of external load or frequency management methods you haven't previously mentioned, or discovered), we can talk a little more about what might be occurring when the plant gets separated from the grid that causes upsets and then you can tell us if that is, in fact, what is happening.

I HAVE NOT looked over the SLD (Single Line Diagram) as there is too much we don't know about the rest of the plant and control system. Forgive me for not looking at the drawing, but I've just been given a very similar question about grid frequency disturbances and Mark VI response--and very late in the review have been told there is an external load/frequency control system that is overriding the Mark VI's. And that should have been made clear at the beginning, but wasn't. And, we can't see the .m6b file running in the Mark VI's.

Fun, fun, fun.

NOT.

Anyway, we need clarification, minus any mention of external load/frequency controls, and we can possibly proceed further.
 
hi guys

thank so much for your responses and sorry for the time i took to response, i was trying to recolect more info but its kind of hard
i been asking to my collegues about the island mode
but i get more and more doubts

what has happen here is that the unit, because of an external issue, open all the breakers 52G and go to a mode I (L3FXI)
and then FSNL providing the load of the UAT (hotel load) and here they call that island mode.
but as SCA says that is not possible (why) its only a name issue? we got a confussion of names i think
so island mode equals to isoch mode?


1597287299583.png


1597287339486.png



"LOAD REJECT (L83FXI) In this mode, the fuel is passed through the G2 and G3 valves to the PM1 and PM3 passages, respectively. PM1 fuel is scheduled with a fixed split, FXKSP1I. This is only a transient mode that is triggered during a breaker open event when operating in a premix mode. A load rejection (breaker open event) from any mode that utilizes diffusion fuel will transition to Mode 1D. The unit online status signal, L52ONLINE, is driven to 0 (False) when there is a breaker open event. The drop out of L52ONLINE initializes two timers that begin a countdown for K83FXLMN_Z and K83FLMX_Z seconds which drive signals L83FXLMN_Z and L83FXLMX_Z. These signals provide an upper and lower boundary for when the speed recovery logic, L83FXL_Z, triggers a transfer to Mode 1D FSNL from either a Diffusion anchored (D5) load rejection event or a Premix anchored (PM1+PM3) load rejection event. The minimum timer is coupled with L33FSRN, which is triggered when the speed fuel stroke reference (FSRN) is equal to the minimum fuel stroke reference (FSRMIN) after the overspeed event has occurred during the load rejection.LOAD REJECT (L83FXI) In this mode, the fuel is passed through the G2 and G3 valves to the PM1 and PM3 passages, respectively. PM1 fuel is scheduled with a fixed split, FXKSP1I. This is only a transient mode that is triggered during a breaker open event when operating in a premix mode. A load rejection (breaker open event) from any mode that utilizes diffusion fuel will transition to Mode 1D. The unit online status signal, L52ONLINE, is driven to 0 (False) when there is a breaker open event. The drop out of L52ONLINE initializes two timers that begin a countdown for K83FXLMN_Z and K83FLMX_Z seconds which drive signals L83FXLMN_Z and L83FXLMX_Z. These signals provide an upper and lower boundary for when the speed recovery logic, L83FXL_Z, triggers a transfer to Mode 1D FSNL from either a Diffusion anchored (D5) load rejection event or a Premix anchored (PM1+PM3) load rejection event. The minimum timer is coupled with L33FSRN, which is triggered when the speed fuel stroke reference (FSRN) is equal to the minimum fuel stroke reference (FSRMIN) after the overspeed event has occurred during the load rejection."
 
hi guys

thank so much for your responses and sorry for the time i took to response, i was trying to recolect more info but its kind of hard
i been asking to my collegues about the island mode
but i get more and more doubts

what has happen here is that the unit, because of an external issue, open all the breakers 52G and go to a mode I (L3FXI)
and then FSNL providing the load of the UAT (hotel load) and here they call that island mode.
but as SCA says that is not possible (why) its only a name issue? we got a confussion of names i think
so island mode equals to isoch mode?


View attachment 449


View attachment 450



"LOAD REJECT (L83FXI) In this mode, the fuel is passed through the G2 and G3 valves to the PM1 and PM3 passages, respectively. PM1 fuel is scheduled with a fixed split, FXKSP1I. This is only a transient mode that is triggered during a breaker open event when operating in a premix mode. A load rejection (breaker open event) from any mode that utilizes diffusion fuel will transition to Mode 1D. The unit online status signal, L52ONLINE, is driven to 0 (False) when there is a breaker open event. The drop out of L52ONLINE initializes two timers that begin a countdown for K83FXLMN_Z and K83FLMX_Z seconds which drive signals L83FXLMN_Z and L83FXLMX_Z. These signals provide an upper and lower boundary for when the speed recovery logic, L83FXL_Z, triggers a transfer to Mode 1D FSNL from either a Diffusion anchored (D5) load rejection event or a Premix anchored (PM1+PM3) load rejection event. The minimum timer is coupled with L33FSRN, which is triggered when the speed fuel stroke reference (FSRN) is equal to the minimum fuel stroke reference (FSRMIN) after the overspeed event has occurred during the load rejection.LOAD REJECT (L83FXI) In this mode, the fuel is passed through the G2 and G3 valves to the PM1 and PM3 passages, respectively. PM1 fuel is scheduled with a fixed split, FXKSP1I. This is only a transient mode that is triggered during a breaker open event when operating in a premix mode. A load rejection (breaker open event) from any mode that utilizes diffusion fuel will transition to Mode 1D. The unit online status signal, L52ONLINE, is driven to 0 (False) when there is a breaker open event. The drop out of L52ONLINE initializes two timers that begin a countdown for K83FXLMN_Z and K83FLMX_Z seconds which drive signals L83FXLMN_Z and L83FXLMX_Z. These signals provide an upper and lower boundary for when the speed recovery logic, L83FXL_Z, triggers a transfer to Mode 1D FSNL from either a Diffusion anchored (D5) load rejection event or a Premix anchored (PM1+PM3) load rejection event. The minimum timer is coupled with L33FSRN, which is triggered when the speed fuel stroke reference (FSRN) is equal to the minimum fuel stroke reference (FSRMIN) after the overspeed event has occurred during the load rejection."
Hi all,


Looks like I was right from the beginning, there is surely ( you are surely ) a misunderstood /confused on Island mode/isochoronous mode!

ControlsGuy25.
 
ratm,

If the people at the site where you collect your pay want to call something by whatever name(s) they choose--you should adopt their terminology. Many other sites around the world use different terminology, and ControlsGuy25 (being the omniscient telepath he is) and I were simply trying to be sure we were answering the proper question. (We are; but our efforts have been wasted.)

Let's try this, and then I'm going to drop off the thread. To my mind and experience a power producing site doesn't get paid for producing the power required to operate the equipment on the powerproducing site. They only get paid for producing power that supplies loads outside of the power-producing site. That could be either supplying a grid, or supplying a process or plant (such as a chemical plant or a refinery or a cement plant or a factory) independent of a grid. In most power-producing plants and parts of the world the latter (supplying loads--other than the power required to operate the power-generating equipment--independent of a grid and getting paid to do so) is called islanded operation. A "power island" is a group of loads that is operating independently of a grid--think of a small island in an ocean that doesn't get power from a grid on the nearby mainland and has to produce its own electrical power to supply the motors and televisions lights and computers and computer monitors on the island. "Island" is a metaphor for an independent area of electrical loads being powered independently of a grid, by a power plant that is not connected to a grid.

If the people that collect a paycheck at the plant where you work want to call a 200 MW gas turbine providing a couple or four MWs to operate the turbine and its auxiliaries an island, or to say that is a power island--as long as they continue to pay you then you should conform to their way of thinking. Just be aware that when you are discussing things that happen at your plant with people outside your plant YOU are going to have to think long and hard about the discussions and the terms and conditions. This is one of those times when using a non-native language to discuss specific technical terms means there are going to be misunderstandings and confusion.

Welcome to the global community where words and terms can have very different meanings depending on where in the world they are being used.

That's me--I'm completely finished with thread. Now someone at your plant is confusing load rejection with islanded operation in addition to hotel load. That's more confusion than I can deal with. "If you can't dazzle them with brilliance, baffle them with bullshit." I hope you are wearing shoes with high tops because the level of bullshit is rising to near your ankles, mate.

I don't know what your job is supposed to be at the place where you are collecting your pay, but best to keep a lower profile and maybe stop posting to international technical forums and then discussing it with "technicians" at the place where you get paid. 'Cause they might decide to stop paying you....

Best of luck in your career.
 
Hello all,

CSA ,

I am not just omniscient telepath .... I do not know where this idea come from , I take it as a joke (LOL), I know that there is nothing wicked with joking sometimes, so I do not take it personnaly.

RATM,CSA

My post is clear, ( on my first post I clearly explained that to Ratm that he was misunderstanding /confused with his plant control concept.

I deleted one line about isochronous mode to get Ratm aware about his misunderstanding/confusion) .

Now for me it is more clear (not clear at 100%) that Ratm was confused by the plant operating control concept ( specially for house load/hotel load vs island mode)

After seen the screen shot , I see that one signal named L83SCI_CMD "island frequency control mode" output of rung-252 ???

As we do not have the site app code ,I cannot add comments .

There are some other signals needed to be clarified , like R43SCI& R43SCD, Can you devellop on this.???

ControlsGuy25.
 
ControlsGuy25, yes the omniscient telepath comment was my feeble attempt at humor.

I'm frustrated and annoyed at this thread and the original poster. He's in over his head, and he's listening to people who don't know and can't explain what they are talking about. Never mind their use of terms and words. And now ratm is on to another thread and concept, and, well, I wish him all the best.

You were right, of course--BUT, you didn't explain precisely why and how you were right. You didn't offer any explanation, or at least the explanation was not nearly detailed enough for ratm. And, now he's gone and gotten these pictures of rungs that are totally irrelevant to the question. Yes, when the 52G breaker opens if the unit has to keep flame on without tripping on loss of flame because the fuel is cut back so severely because of the loss of load, then it has to transition these combustion modes to do so. BUT THAT HAS NOTHING TO DO WITH ISLAND MODE OR ISOCHRONOUS SPEED CONTROL MODE. Zero. Zilch. Nada. Niente. Zippo. Nothing whatsoever. It's rubbish--it's an attempt by people at his site to make him go away, and he's using it to confuse us (at least me). The reason the fuel was cut back to severely is because 52G opened--I don't care if the unit can or even should be self-sustaining (capable of being able to keep the auxiliaries running when 52G is opened suddenly). This logic/application code is irrelevant to the original question, which keeps coming back to haunt us, which is: When should the unit be in island mode? (Really, when should it switch to Isochronous Speed Control? BUT, NOOOOO!!!!!)

Sometimes one just has to cut their losses, turn and walk away.

This is me cutting my losses, turning and walking away.

And recommending others do the same.
 
Ok....i will stop posting in this thread...i understood your point...thanks a lot for your responses it was very usefull
 
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