Synchronization of Multiple Generators onto the Grid

Hello,

I will do commissioning tests for a plant synchronization system to control a group of turbine generators (2 ~ 3 generators together) to be synchronized onto the grid. FYI, GE CTG rating: 40 MW & Siemens STG rating: 82 MW. For our system, at least 1xCTG, and 1xSTG are to be controlled together for generation bus synchronization with the grid. Of course, the generation bus with multiple generators runs in island mode.

To me, this situation would be quite challenging since CTG & STG controller's responses are not the same. So, I am really concerned if this synchronization would really work although it would take a quite long time.

Do you have any experiences with the synchronization of multiple generators onto the grid? Do you have any thoughts and/or advice? Anything will be very helpful for me.

Thanks in advance.
 
skyimk,

Hundreds of turbine-generators of all sizes and types are synchronized together on islanded grids in many locations around the world every day. How? Because they are adhering to basic AC (Alternating Current) fundamentals for synchronous generators.

You would need to tell us quite a lot more about the island and how the units are being controlled for us to be able to begin to help with your doubts and concerns. If the island uses some kind of over-all “power management system” to try to control frequency in response to load variations and changes then there will likely need to be some tuning of control parameters involved. But since most “power management systems” are unique and very few are alike and many use unique terms and configurations it would be nearly impossible for anyone to say how the system at this island will work.

A good and proper understanding of Droop Speed Control is the best thing for a situation like this because that is key to understanding interactions between turbine-generator control systems. From your post it would appear there is some other source of steam for the steam turbine (since the exhaust heat from a single 40 MW CTG (Combustion Turbine-Generator) can’t produce 80 MW of steam, so there’s a lot of information you haven’t told.

Again, a good, solid understanding of Droop Speed Control basic AC power generation fundamentals will be key to knowing what is supposed to happen and if it is happening or not. And if there is some kind of “power management system” for frequency and load control at the facility you will likely have to study it closely to determine if it is working correctly or requires adjustment (“tuning”).

Best of luck in your endeavour!
 
Hi CSA,

First of all, sorry for the incomplete information. Here is some more information.

This is the combined cycle cogeneration plant which consists of 3 x CTGs / 2 x STGs. Plant load is approx. 180~190MW and will export approx. 80MW to the grid. CTGs were supplied by GE, and Siemens supplied STGs. Of course, we have the power management system (PMS) which controls all TG units in the grid interconnected mode and island mode of the plant., i.e., MW export/PF control in the grid-connected mode and frequency/voltage control in the island mode.

Each TG unit is directly connected to a GSU transformer, then all GSU transformers are connected to EHV SWYD where is defined as a point of interconnection with the grid. EHV SWYD has 2 incoming breakers for grid interconnection and 1 bus tie-breaker. The plant synchronization controller has been designed to close these EHV breakers (of course, one breaker at a time) by controlling multiple generators on the island bus. I also attached an example island bus configuration that we are attempting to close bus tie-breaker but GSU transformers are not shown on the sketch.
Example Island Bus Configuration.JPG
Just for my past experiences, I had experienced with PMS as well as multiple generator control for 2 x island bus synchronization as an engineer in EPC contractor. But all generators were the same rating in that project. So, it was much easier for me to design and operate the island power system but it took much longer in island bus synchronization (i.e., bus tie breaker closure of main generation/distribution bus) when we had controlled multiple generators. I guess that the timing of pulse outputs from the synchronizer to each TG controller might be slightly out of synch, and this slightly misaligned timing might cause a bit longer synchronizing time with multiple generators.

This is why I am concerned about synchronization control and a synch time if we have different sizes of TG units in the island bus, as shown on the sketch, we would not achieve island bus synchronization onto the grid when we will have 1xCTG and 1xSTG or 2xCTGs and 1xSTG on the same island bus.

But in the meantime, I am also thinking it would be OK since all CTGs & STGs will run in speed control and voltage control mode and have the same droop setting but would take much longer than expected. Anyway, I might be getting too worrisome for nothing but better to check before trouble and just want to have more self-confidence on this topic. To me, PMS control is easier than synchronizing control of multiple generators.

I wish all the above information would be sufficient for you, CSA. If you need more information, let me know.
 
In my experience, the length of the pulses used to change speed reference (and therefore load) are one of the most important things to be “tuned.” All grids have machines synchronized to them and while many have the same percentage droop regulation setpoint and different load capabilities (maximum load) they will all respond a little differently—but they should all respond in a similar manner as regards accepting or reducing load.

In my personal experience, PMS’s are the real problem—especially when they are configured and programmed by people who don’t know droop speed control and don’t understand island ”grids.” And then during commissioning there are all numbers of “experts” on site in the Control Room who don’t really know much at all, except, “That’s not how we did it on the last job!”And they can’t explain how it was done on the last job. And they just have these opinions about how it should work without ever having thought about what they are saying and if it’s even feasible—but they’re certain it’s not operating properly and whatever changes the commissioning person wants to make are incorrect.

I hope you have the plant design and operation plan as well as understand the PMS configuration and programming enough to dig into it and understand the operation and be able to compare it to the intended plant operation so you can identify any changes in programming or se points necessary to make the plant operate smoothly and as intended.

Personally, I am not a fan of most PMS’s. And most of the issues I have had with island operation were the result of poor PMS configuration and programming. But of course the people who provided the PMS are adamant the problem IS NOT with their equipment.

Best of luck. Be safe—and stay healthy!!!
 
skyimk,

I also want to mention that many STG's used in combined cycle applications operate differently than most other STG's--because they are "captive" to the CTG's and their loads and exhaust heat. Many STG's used in combined cycle applications just open their control valves wide open after an initial warm-up and loading period. They just take whatever steam is available at whatever temperature and produce as much power with it as they can. This can GREATLY complicate matters for islanded operation of combined cycle plants because it's difficult to send a command to load or unload a STG when the control valves are already wide open.

So, you should also be checking with the STG control system programmers to see how they will handle load commands in islanded operation. Will the control valve(s) always be wide open during islanded operation? What happens when GT exhaust flow and temperature suddenly change?

I think this will also complicate re-synchronization with the grid.... And could be the cause of the long period required for re-synch you seem to be talking about. When re-synching with the grid it would probably be best to switch (one of) the CTG('s) to Isochronous Speed Control mode and use it to synch the island with the grid. It would seem that trying to do it with the PMS would be very difficult, trying to hold the CTG AND STG speeds constant long enough to match speed/frequency with the grid and re-close the grid tie breaker. And, once the generator breaker closes the unit running in Isoch mode must quickly switch back to Droop Speed Control or there's going to be problems....!

That's all I can add to this thread. I don't know when you will be commissioning this plant, but it would be great to hear back from you about your experience and what it took to get the plant running smoothly and re-synch'ing smoothly.

I can tell you, that when I'm in a control room when this part of commissioning is going on--I always have a fully-charged torch (flashlight) in my pocket. (I almost ALWAYS carry a torch when working in a power plant..... especially during commissioning, but especially when trying to run in island operation, and re-synch'ing with the grid.)

Best of luck!!!
 
I have a doubt on the same subject and could you clarify?

In a plant (A), 3 turbine generators are running in parallel with load. Lets say 10MW power margin is available... This plant is connected to the nearest plant (B) for emergency purpose and Plant (B) is powered from another plant (C) 100kM away from Plant (B).

During an emergency situation or maintenance purpose, Plant (A) need to feed 10MW to Plant (B). In order to avoid plant (B) shutdown, it should synchronise with Plant (B) before open power from Plant (C).

The Plant (B) has the facility to synchronize with the plant (A) from Plant (B).
But how can we synchronize the 3 running generators in Plant (A) from Plant (B)? Especially how we will raise or lower the speed of the 3 running generators together in the plant (A) from Plant (B) for synchronization? Is it practically possible?
 
I have a doubt on the same subject and could you clarify?

In a plant (A), 3 turbine generators are running in parallel with load. Lets say 10MW power margin is available... This plant is connected to the nearest plant (B) for emergency purpose and Plant (B) is powered from another plant (C) 100kM away from Plant (B).

During an emergency situation or maintenance purpose, Plant (A) need to feed 10MW to Plant (B). In order to avoid plant (B) shutdown, it should synchronise with Plant (B) before open power from Plant (C).

The Plant (B) has the facility to synchronize with the plant (A) from Plant (B).
But how can we synchronize the 3 running generators in Plant (A) from Plant (B)? Especially how we will raise or lower the speed of the 3 running generators together in the plant (A) from Plant (B) for synchronization? Is it practically possible?
You should better provide A SLD for better understanding...
As there is one point not clear for me on your description of these plants configuration..
 
Hi .. Thanks for your reply.... See the hand drawn SLD .. please let me know any further clarification is required.
My main doubt is how we can adjust the speed of individual or all GTS at the same time when 3 GTS are running in parallel fro synchronization from Plant B. Plant B is 500m away from plant A. Which is the best configuration of Plat A ? droop etc?

1665884222106.png
 
Hi .. Thanks for your reply.... See the hand drawn SLD .. please let me know any further clarification is required.
My main doubt is how we can adjust the speed of individual or all GTS at the same time when 3 GTS are running in parallel fro synchronization from Plant B. Plant B is 500m away from plant A. Which is the best configuration of Plat A ? droop etc?

View attachment 2477
Hi

Thank you for your reply

I have read the original post and i come to this question....

Are you sure about this sentence that you wrote: The Plant (B) has the facility to synchronize with the plant (A) from Plant (B).


I guess that one should read: The Plant (A)& Plant (B) has the facilities to synchronize plant (A) with the plant (B) ..

Can you clarify on this sentence as it can be bit confusing ..

Otherwise about SLD and plants( Units) synchronization, here some notes:

We should see Line circuit breaker also called 52L and also Generator circuit breaker 52G on the SLD for better understanding..

It is written emergency connection once in 3 years ...does it mean that Plant B got his Line bus "dead" OR Still "alive " and fed from Plant C or there is kind of Tie line breaker so Plant B can be isolated from Plant C on this configuration?

There will be more questions coming as long as i reviewing the SLD..

You asked about Speed control/regulation on the 3 GTGs /units it is much about their prime mover not geneerator itself that speed regulation is done.

Also you wrote No generator control on Plant C ...it is more about AVR /GCP (called Generator control panel)

Can you clarify on that point ..( GTGs units shoudl got their own GCP)..

Also can we knwo bit more about plants utilities ( cement plant, factory , other processes)

Regards,
James
 
pbsubhash,

There re may things which aren't very clear about your description of the plants and their connection to the grid. THIS EXPLANATION SUPPOSES THAT PLANTS A & -C ARE NOT CONNECTED TO THE GRID AND THAT ONLY PLANT B IS CONNECTED TO THE GRID (THE SAME GRID--NOT DIFFERENT GRIDS). PLANT A AND PLANT C MAY BE SUPPLYING LOADS INDEPENDENTLY OF A GRID BUT THEY ARE NOT CONNECTED IN PARALLEL. THIS EXPLANATION ALSO SUPPOSES THAT THERE IS A BREAKER BETWEEN PLANT A AND PLANT B WHICH IS THE BREAKER WHICH IS USED TO PARALLEL (SYNCHRONIZE) PLANT A WITH PLANT B (THE BREAKER IS NOT SHOWN ON THE DRAWING). THE NOTE "EMERGENCY CONNECTION-ONCE IN THREE YEARS" MEANS THE BREAKER USED TO PARALLEL (SYNCHRONIZE) PLANT A AND PLANT B HAS ONLY EVER BEEN CLOSED ONCE IN THREE YEARS; IN OTHER WORDS, PLANT A AND PLANT B ARE NOT USUALLY CONNECTED (PARALLELED; SYNCHRONIZED) WITH EACH OTHER. FURTHERMORE, THE GAS TURBINE-GENERATORS AT PLANT A ARE ALL THREE OPERATED IN DROOP SPEED CONTROL MODE--WITH A "PMS" (POWER MANAGEMENT SYSTEM) PROVIDING THE SIGNALS TO THE THREE GAS TURBINE-GENERATOR CONTROL SYSTEMS (GOVERNORS AND AVRS (AUTOMATIC VOLTAGE REGULATORS) TO MAINTAIN FREQUENCY AND VOLTAGE (VAr OR POWER FACTOR). THE PMS MONITORS THE FREQUENCY OF PLANT A AND ADJUSTS THE SPEEDS OF THE THREE GAS TURBINE-GENERATORS BY SENDING RAISE- AND LOWER SPEED SIGNALS TO THE THREE GAS TURBINE GOVERNORS. THE PMS MONITORS THE VOLTAGE (AND PROBABLY THE VAr AND POWER FACTOR) OF PLANT A AND SENDS RAISE- OR LOWER VOLTAGE SIGNALS TO THE THREE GENERATOR AVRs TO MAINTAIN THE PLANT VOLTAGE AND/OR VAr OR POWER FACTOR.

Based on the suppositions as stated above, Plant A would be the "incoming" power to Plant B and Plant B would be the "running" or "bus" of the intended synchronized system. The easiest way to synchronize Plant A with Plant B would be to use the PMS of Plant A to adjust the voltage of Plant A to be equal to or slightly greater than the voltage of Plant B AND to use the PMS of Plant A to adjust the frequency of Plant A to be just slightly greater than the frequency of Plant B. Then, at the appropriate time (when the three phases of Plant A and Plant B are in phase opposition--when the synchroscope of the breaker between Plant A and Plant B is very nearly at the 12 o'clock position as it rotates in the clockwise direction the signal to close the breaker between Plant A and Plant B would be issued, the breaker between Plant A and Plant B would close, and the two plants would be synchronized.

At that instant in time it would be necessary to "disable" the PMS of Plant A as Plant A would be synchronized with the grid though Plant B, and the voltage and frequency of Plant A would be primarily controlled by the grid to which Plant B is connected. The loads of the three turbine-generators (MW; megawatts) would, if the grid frequency were stable, remain at what they were just prior to when the breaker between Plant A and Plant B was closed. It would likely be necessary to used the AVR Raise- and Lower Voltage controls of the three generator AVRs to balance reactive load and adjust the VAr or Power Factor of the three generators. If it was necessary to change the loads of the three turbine-generators (MW; megawatts) it would be necessary to use the Raise- and Lower Speed controls of the three turbine governors to do so.

When it was desired to separate Plant A from Plant B, all that would need to be done was to ensure that as soon as the breaker between Plant A and Plant B opened that the PMS of Plant A would be enabled (become active) and that its load setpoint (MW; megawatt) would be equal to the present output of Plant A. If the present output (MW; megawatts) of Plant A exceeded the power required by the loads being supplied by Plant A the PMS would adjust the three gas turbine governors to maintain frequency (by lowering the Speed setpoints of the governors operating in Droop Speed Control mode). The PMS would adjust the voltage setpoints of the three generator AVRs to maintain the desired Plant A voltge (and/or VAr or Power Factor).

That's it--supposing there is a PMS at Plant A. If there's no PMS at Plant A, then it's likely either the three turbine governors are operating in some kind of Isochronous Load-sharing mode (essentially a de-tuned Isochronous Speed Control Mode) we would need to know a LOT about how that mode operates and if it can be manually enabled and disabled.

If there is no PMS at Plant A and the three turbine governors of Plant A ARE NOT being operated in some kind of Isochronous Load-sharing mode, then it's pretty likely that one of the three turbine governors is operating in Isochronous Speed Control mode and the other two are operating in Droop Speed Control mode. In that case, the governor of the Plant A gas turbine-generator operating in Isochronous Speed Control Mode could be used to synchronize Plant A with Plant B--BUT, immediately on closure of the breaker between Plant A and Plant B the governor of the gas turbine operating in Isochronous Speed Control mode would have to be switched to Droop Speed Control Mode.

This explanation also presumes that the loads (MW; megawatts) and voltages of Plant A and Plant B (the grid) are stable and not fluctuating excessively either during synchronization or during synchronized (parallel) operation.

If Plant B is connected to other, larger or more numerous generators and their prime movers it will be very unlikely that you (or anyone) will be able to control the speed of the three gas turbine generators--because once SYNCHRONIZED to the grid the grid controls frequency (which is directly proportional to speed--so the grid controls the speed of ALL generators and their prime movers which are synchronized to the grid). Individual generator terminal voltages and resultant VAr and Power Factor readings can be somewhat affected by the individual generator AVR controls (Raise- and Lower Voltage controls).

That's it. That should allay any and all of your doubts. Once and for all.

Full stop. Period.

End of discussion.
 
When one, two, nine, 26, 109 or several hundred generators are SYNCHRONIZED together on a grid the speed of all the generators (which is a function of the frequency of the grid the generators are synchronized to!) is the same. (Yes; there can be and will be very small differences, probably hundredths or thousandths of a Hertz, but not one, two or three Hertz.) Generators are big magnetic systems--and when they are SYNCHRONIZED together it's like having two or three or 20 or more small magnets stuck together. All the North Poles are drawn to the South Poles (unlike poles attract)--and it takes a LOT of force to separate them and even MORE force to try to force the two North Poles of two magnets together which means you are ALSO trying to force the two South Poles together, also. You MIGHT actually get them to touch but as soon as you release them--WHAMMMM!!! They either fly apart or they turn VERY FAST and the North and South Poles stick to each other. That's what SYNCHRONISM is basically all about--magnetic attraction (and repulsion). And the magnetic poles that exist inside synchronous generators are VERY strong.

The other thing most people "forget" about AC (Alternating Current) systems is that the most important thing is stable frequency. And the frequency of a synchronous AC generator (more properly called an alternator) is a direct function of the speed of the generator. They all see that synchronous generators are started and accelerated to synchronous speed, and then, when the generator breaker closes (when the generator is synchronized with one or more other generators (and their prime movers)) they just assume that the generator speed increases with load. But it DOESN'T--it stays constant, because it has to generate AC at a constant frequency (which means the generator has to operate at a constant speed). Yes; when more fuel is put into the gas turbine (if that's the generator's prime mover) it will TRY to speed up--but it can't. The grid won't let it. And that increase in torque from the increased fuel causes more amperes to flow out of the generator terminals. And THAT'S what increases the load (MW; megawatts) on the generator. Amperes are a function of torque, and torque is a function of fuel (energy input to the prime mover).

So, Plant A--once it's synchronized to a grid with other generators and their prime mover--wants to (is forced to, really) operated at a constant speed/frequency. Because of the magnetic forces inside all the generators which are synchronized together.

It's pretty simple, really. But, most people forget about magnetism inside synchronous generators (or even electric motors for that matter) and they forget about the relationship between speed and frequency. Synchronism. It's a VERY POWERFUL concept, which makes it a very powerful word. It isn't just important when connecting a generator and its prime mover to other generators and their prime movers--it is what holds the speed/frequency of ALL the generators and their prime movers operating in parallel (synchronism) the same.

Think about it--if one synchronous generator is operating at 49.17 Hz and another is operating at 51.34 Hz how is that when you measure the current at the electrical socket in the wall that it's 50.03 Hz? There's no "smoothing" equalizing devices on an AC power transmission and distribution system to take the outputs of generators operating at different frequencies and turn them all into "50 Hz." It's the magnetic forces at work inside the synchronous generators that do that--do a very good job of forcing all the generators to run at essentially the SAME frequency--desirably "50 Hz" (or 60 Hz depending on where one is in the world or where one is talking about). And, all of those generators and their prime movers do this without ANY control signals being shared between all of the power plants--NONE. It's all a function of frequency, which is a function of speed. It's genious, really. So simple, it's genious.

Textbooks and reference books don't come out and say this--and most professors don't, either. But, it's the way things work.

:unsure:

Things that make you go, "Hmmmmm!!!!!!"
 
pbsubhash,

I want to be very clear about the three gas turbine-generators at Plant A. If they are all connected to the same bus (as shown in the SLD (Single-Line Diagram)) then they will ALL run at the same speed and frequency. One turbine-generator cannot run at 98.6% speed/frequency, another at 100.76% speed/frequency and the last at 102.39% speed/frequency. That just can't happen. And, if the three gas turbine-generators at Plant A are isolated from other generators and prime movers then increasing the speed reference of one of the three turbine-generators will increase the speed of ALL of the three turbine-generators. THIS SUPPOSES THE THREE GAS TURBINE-GENERATORS ARE ALL NEARLY EQUAL IN CAPACITY/RATING, AND EVEN SMALL DIFFERENCES BETWEEN THE THREE WOULDN'T CAUSE DIFFERENT RESULTS WHEN CHANGING THE SPEED REFERENCE OF ONE OF THE TURBINE-GENERATORS. IF ONE TURBINE-GENERATOR IS MUCH LARGER THAN THE OTHER TWO AND THE SPEED REFERENCE OF ONE OF THE SMALLER TURBINE-GENERATORS WAS INCREASED THAT PROBABLY WOULDN'T RESULT IN THE SAME SPEED/FREQUENCY INCREASE--BUT IT WOULD CAUSE SOME INCREASE IN SPEED/FREQUENCY.

Again, these three replies are all based on the information provided AND the suppositions stated (usually in sentences written in all capital letters). It can be very difficult to answer questions like this when all of the circumstances aren't clearly stated in the problem definition. However, the physics of alternating current generation and governor speed control and generator frequency dictate that unless there are large differences in capacity between the three turbine-generators of Plant A that any single turbine-generator can be used to "match" speed/frequency and most likely even voltage for the purposes of synchronizing Plant A and Plant B. And, regardless of the capacity (rating) differences of the three turbine-generators at Plant A if they are all connected to the same bus then they are all synchronized together and all will run at the same speed/frequency.

One final note: ALL REFERENCES TO SPEED HERE ARE REFERENCES TO PERCENT OF SYNCHRONOUS SPEED. IF THE GENERATOR IS RATED AT 50 Hz AND HAS TWO POLES, IT NEEDS TO TURN AT 3000 RPM--WHICH IS THE SYNCHRONOUS SPEED OF THE GENERATOR. THE SYNCHRONOUS SPEED OF THE GAS TURBINE COUPLED TO THE TWO-POLE GENERATOR IS THE GAS TURBINE SPEED THAT RESULTS IN 3000 RPM OF THE TWO-POLE GENERATOR IT IS COUPLED TO; THAT MIGHT BE 5134 RPM, OR 3000 RPM, OR 5129 RPM.

The fact remains--if the three turbine-generators of Plant A are all running and connected to (synchronized to) the same bus that will be synchronized to the bus of Plant B, then all three turbine-generators of Plant A are running at the same percent of synchronous speed--the SAME frequency. Changing the speed reference of one of the three turbines WILL change the speeds of all three turbines (and generators) by the same percentage--BECAUSE THEY ARE SYNCHRONIZED TOGETHER ON THE SAME BUS. MAGNETIC FORCES WILL NOT ALLOW ANY GENERATOR(S) TO OPERATE AT ANY SPEED OTHER THAN THE SPEED OF ALL THREE GENERATORS AS A GROUP.

Hope this clarifies any remaining doubts.

Note that when the speed reference of one of the turbine-generators at Plant A is changed the frequency of the loads being supplied by Plant A will also change by the same amount (as will the frequency of all three turbine-generators). Synchronism. It's a very powerful word--and a very powerful physical principle. Again, think of the frequency coming out of the electrical outlet on the wall; ALL the generators connected (SYNCHRONIZED) together are all spinning at the same speed and operating at the same frequency as the frequency of the current coming out of the electrical outlet in the wall. It can't be any other way. Period. Full stop.

Now, if the three gas turbine-generators are connected to (synchronized to) other generators and their prime movers then it will be nearly impossible to synchronize Plant A from Plant B. So, that's another supposition made for the purposes of these replies: PLANT A IS OPERATING INDEPENDENTLY OF ANY OTHER GENERATORS AND PRIME MOVERS--IT IS NOT CONNECTED TO (SYNCHRONIZED TO) ANY OTHER GENERATORS AND PRIME MOVERS WHEN TRYING TO SYNCHRONIZE (CONNECT) TO PLANT B.

I think that covers all of the perversions which might be brought up. If you have other conditions or circumstances, please try to be as specific as possible because as you read here circumstances do matter.

Best of luck! Hopefully we have answered your questions ("doubts") and provided sufficient background information and details to understand why what was written was written.
 
Hi

Thank you for your reply

I have read the original post and i come to this question....

Are you sure about this sentence that you wrote: The Plant (B) has the facility to synchronize with the plant (A) from Plant (B).


I guess that one should read: The Plant (A)& Plant (B) has the facilities to synchronize plant (A) with the plant (B) ..

Can you clarify on this sentence as it can be bit confusing ..

Otherwise about SLD and plants( Units) synchronization, here some notes:

We should see Line circuit breaker also called 52L and also Generator circuit breaker 52G on the SLD for better understanding..

It is written emergency connection once in 3 years ...does it mean that Plant B got his Line bus "dead" OR Still "alive " and fed from Plant C or there is kind of Tie line breaker so Plant B can be isolated from Plant C on this configuration?

There will be more questions coming as long as i reviewing the SLD..

You asked about Speed control/regulation on the 3 GTGs /units it is much about their prime mover not geneerator itself that speed regulation is done.

Also you wrote No generator control on Plant C ...it is more about AVR /GCP (called Generator control panel)

Can you clarify on that point ..( GTGs units shoudl got their own GCP)..

Also can we knwo bit more about plants utilities ( cement plant, factory , other processes)

Regards,
James
Sorry for the mis-understanding due to my SLD. This is for my own study and PLANT A is not a real installed scenario.. Just curious to know how it will work if connected this way.
Plant A & B considered both have synchronizing facility.
Plant A should be continuously working with its own loads and Plant C also continuously working with its ownload but with Plant B loads. Plat A & C will never working in parallel in normal operation and need to do momentary paralleling in case plant A need to supply Power to Plant B . Actually here, there is no grid .. I wrongly mention Plant C as Grid. Sorry for that.

I am not an expert on the generator control and my understanding is 3 GTGs on plant A will set in droop mode and adjust the Voltage and frequency from Plant B then it will momentary synchronize with Plant C generators. Once it is synchronized, Plant C breaker to Plant B will be open. Then plant C can do their planned maintenance. My question was is it Easy to do synchronization when 3 GTS are running at Plant A with Plant C Generators to feed power to Plant B from A.

Thank you very much for your time for explanation .

regards
 
pbsubhash,

There re may things which aren't very clear about your description of the plants and their connection to the grid. THIS EXPLANATION SUPPOSES THAT PLANTS A & -C ARE NOT CONNECTED TO THE GRID AND THAT ONLY PLANT B IS CONNECTED TO THE GRID (THE SAME GRID--NOT DIFFERENT GRIDS). PLANT A AND PLANT C MAY BE SUPPLYING LOADS INDEPENDENTLY OF A GRID BUT THEY ARE NOT CONNECTED IN PARALLEL. THIS EXPLANATION ALSO SUPPOSES THAT THERE IS A BREAKER BETWEEN PLANT A AND PLANT B WHICH IS THE BREAKER WHICH IS USED TO PARALLEL (SYNCHRONIZE) PLANT A WITH PLANT B (THE BREAKER IS NOT SHOWN ON THE DRAWING). THE NOTE "EMERGENCY CONNECTION-ONCE IN THREE YEARS" MEANS THE BREAKER USED TO PARALLEL (SYNCHRONIZE) PLANT A AND PLANT B HAS ONLY EVER BEEN CLOSED ONCE IN THREE YEARS; IN OTHER WORDS, PLANT A AND PLANT B ARE NOT USUALLY CONNECTED (PARALLELED; SYNCHRONIZED) WITH EACH OTHER. FURTHERMORE, THE GAS TURBINE-GENERATORS AT PLANT A ARE ALL THREE OPERATED IN DROOP SPEED CONTROL MODE--WITH A "PMS" (POWER MANAGEMENT SYSTEM) PROVIDING THE SIGNALS TO THE THREE GAS TURBINE-GENERATOR CONTROL SYSTEMS (GOVERNORS AND AVRS (AUTOMATIC VOLTAGE REGULATORS) TO MAINTAIN FREQUENCY AND VOLTAGE (VAr OR POWER FACTOR). THE PMS MONITORS THE FREQUENCY OF PLANT A AND ADJUSTS THE SPEEDS OF THE THREE GAS TURBINE-GENERATORS BY SENDING RAISE- AND LOWER SPEED SIGNALS TO THE THREE GAS TURBINE GOVERNORS. THE PMS MONITORS THE VOLTAGE (AND PROBABLY THE VAr AND POWER FACTOR) OF PLANT A AND SENDS RAISE- OR LOWER VOLTAGE SIGNALS TO THE THREE GENERATOR AVRs TO MAINTAIN THE PLANT VOLTAGE AND/OR VAr OR POWER FACTOR.

[pbs: Your assumption is exactly same as thought and thank you very much for your valuable time. I am not an expert on this but I doubt there will be no a Centralized PMS to control the all GTGs together but provided PMS system or load sharing system for each GTG Control panel. Is it possible to adjust the voltage and frequency of each generator in droop mode or other two generator will follow the master GTG automatically?

Based on the suppositions as stated above, Plant A would be the "incoming" power to Plant B and Plant B would be the "running" or "bus" of the intended synchronized system. The easiest way to synchronize Plant A with Plant B would be to use the PMS of Plant A to adjust the voltage of Plant A to be equal to or slightly greater than the voltage of Plant B AND to use the PMS of Plant A to adjust the frequency of Plant A to be just slightly greater than the frequency of Plant B. Then, at the appropriate time (when the three phases of Plant A and Plant B are in phase opposition--when the synchroscope of the breaker between Plant A and Plant B is very nearly at the 12 o'clock position as it rotates in the clockwise direction the signal to close the breaker between Plant A and Plant B would be issued, the breaker between Plant A and Plant B would close, and the two plants would be synchronized.
[pbs: Plant C tie-in breaker need to open for Plant C maintenance once the synchronization is established and all the loads at PLANT B is transferred to PLANT A GTGs. During the momentary parallel operation between Plant A & C GTGs how the load sharing will be controlled without affecting Plant A & C running loads? This also i have no idea how to smoothly transfer the loads of Plant B to Plant A which is actually from Plant C. before opening the plant C breaker]

At that instant in time it would be necessary to "disable" the PMS of Plant A as Plant A would be synchronized with the grid though Plant B, and the voltage and frequency of Plant A would be primarily controlled by the grid to which Plant B is connected. The loads of the three turbine-generators (MW; megawatts) would, if the grid frequency were stable, remain at what they were just prior to when the breaker between Plant A and Plant B was closed. It would likely be necessary to used the AVR Raise- and Lower Voltage controls of the three generator AVRs to balance reactive load and adjust the VAr or Power Factor of the three generators. If it was necessary to change the loads of the three turbine-generators (MW; megawatts) it would be necessary to use the Raise- and Lower Speed controls of the three turbine governors to do so.

When it was desired to separate Plant A from Plant B, all that would need to be done was to ensure that as soon as the breaker between Plant A and Plant B opened that the PMS of Plant A would be enabled (become active) and that its load setpoint (MW; megawatt) would be equal to the present output of Plant A. If the present output (MW; megawatts) of Plant A exceeded the power required by the loads being supplied by Plant A the PMS would adjust the three gas turbine governors to maintain frequency (by lowering the Speed setpoints of the governors operating in Droop Speed Control mode). The PMS would adjust the voltage setpoints of the three generator AVRs to maintain the desired Plant A voltge (and/or VAr or Power Factor).

That's it--supposing there is a PMS at Plant A. If there's no PMS at Plant A, then it's likely either the three turbine governors are operating in some kind of Isochronous Load-sharing mode (essentially a de-tuned Isochronous Speed Control Mode) we would need to know a LOT about how that mode operates and if it can be manually enabled and disabled.

If there is no PMS at Plant A and the three turbine governors of Plant A ARE NOT being operated in some kind of Isochronous Load-sharing mode, then it's pretty likely that one of the three turbine governors is operating in Isochronous Speed Control mode and the other two are operating in Droop Speed Control mode. In that case, the governor of the Plant A gas turbine-generator operating in Isochronous Speed Control Mode could be used to synchronize Plant A with Plant B--BUT, immediately on closure of the breaker between Plant A and Plant B the governor of the gas turbine operating in Isochronous Speed Control mode would have to be switched to Droop Speed Control Mode.

This explanation also presumes that the loads (MW; megawatts) and voltages of Plant A and Plant B (the grid) are stable and not fluctuating excessively either during synchronization or during synchronized (parallel) operation.

If Plant B is connected to other, larger or more numerous generators and their prime movers it will be very unlikely that you (or anyone) will be able to control the speed of the three gas turbine generators--because once SYNCHRONIZED to the grid the grid controls frequency (which is directly proportional to speed--so the grid controls the speed of ALL generators and their prime movers which are synchronized to the grid). Individual generator terminal voltages and resultant VAr and Power Factor readings can be somewhat affected by the individual generator AVR controls (Raise- and Lower Voltage controls).

That's it. That should allay any and all of your doubts. Once and for all.

Full stop. Period.

End of discussion.
Thank very much for your valuable time and such a beautiful explanation. :)
 
When one, two, nine, 26, 109 or several hundred generators are SYNCHRONIZED together on a grid the speed of all the generators (which is a function of the frequency of the grid the generators are synchronized to!) is the same. (Yes; there can be and will be very small differences, probably hundredths or thousandths of a Hertz, but not one, two or three Hertz.) Generators are big magnetic systems--and when they are SYNCHRONIZED together it's like having two or three or 20 or more small magnets stuck together. All the North Poles are drawn to the South Poles (unlike poles attract)--and it takes a LOT of force to separate them and even MORE force to try to force the two North Poles of two magnets together which means you are ALSO trying to force the two South Poles together, also. You MIGHT actually get them to touch but as soon as you release them--WHAMMMM!!! They either fly apart or they turn VERY FAST and the North and South Poles stick to each other. That's what SYNCHRONISM is basically all about--magnetic attraction (and repulsion). And the magnetic poles that exist inside synchronous generators are VERY strong.

The other thing most people "forget" about AC (Alternating Current) systems is that the most important thing is stable frequency. And the frequency of a synchronous AC generator (more properly called an alternator) is a direct function of the speed of the generator. They all see that synchronous generators are started and accelerated to synchronous speed, and then, when the generator breaker closes (when the generator is synchronized with one or more other generators (and their prime movers)) they just assume that the generator speed increases with load. But it DOESN'T--it stays constant, because it has to generate AC at a constant frequency (which means the generator has to operate at a constant speed). Yes; when more fuel is put into the gas turbine (if that's the generator's prime mover) it will TRY to speed up--but it can't. The grid won't let it. And that increase in torque from the increased fuel causes more amperes to flow out of the generator terminals. And THAT'S what increases the load (MW; megawatts) on the generator. Amperes are a function of torque, and torque is a function of fuel (energy input to the prime mover).

So, Plant A--once it's synchronized to a grid with other generators and their prime mover--wants to (is forced to, really) operated at a constant speed/frequency. Because of the magnetic forces inside all the generators which are synchronized together.

It's pretty simple, really. But, most people forget about magnetism inside synchronous generators (or even electric motors for that matter) and they forget about the relationship between speed and frequency. Synchronism. It's a VERY POWERFUL concept, which makes it a very powerful word. It isn't just important when connecting a generator and its prime mover to other generators and their prime movers--it is what holds the speed/frequency of ALL the generators and their prime movers operating in parallel (synchronism) the same.

Think about it--if one synchronous generator is operating at 49.17 Hz and another is operating at 51.34 Hz how is that when you measure the current at the electrical socket in the wall that it's 50.03 Hz? There's no "smoothing" equalizing devices on an AC power transmission and distribution system to take the outputs of generators operating at different frequencies and turn them all into "50 Hz." It's the magnetic forces at work inside the synchronous generators that do that--do a very good job of forcing all the generators to run at essentially the SAME frequency--desirably "50 Hz" (or 60 Hz depending on where one is in the world or where one is talking about). And, all of those generators and their prime movers do this without ANY control signals being shared between all of the power plants--NONE. It's all a function of frequency, which is a function of speed. It's genious, really. So simple, it's genious.

Textbooks and reference books don't come out and say this--and most professors don't, either. But, it's the way things work.

:unsure:

Things that make you go, "Hmmmmm!!!!!!"
Really amazing explanation and thank you again for sharing your knowledge....(y)
 
pbsubhash,

I want to be very clear about the three gas turbine-generators at Plant A. If they are all connected to the same bus (as shown in the SLD (Single-Line Diagram)) then they will ALL run at the same speed and frequency. One turbine-generator cannot run at 98.6% speed/frequency, another at 100.76% speed/frequency and the last at 102.39% speed/frequency. That just can't happen. And, if the three gas turbine-generators at Plant A are isolated from other generators and prime movers then increasing the speed reference of one of the three turbine-generators will increase the speed of ALL of the three turbine-generators. THIS SUPPOSES THE THREE GAS TURBINE-GENERATORS ARE ALL NEARLY EQUAL IN CAPACITY/RATING, AND EVEN SMALL DIFFERENCES BETWEEN THE THREE WOULDN'T CAUSE DIFFERENT RESULTS WHEN CHANGING THE SPEED REFERENCE OF ONE OF THE TURBINE-GENERATORS. IF ONE TURBINE-GENERATOR IS MUCH LARGER THAN THE OTHER TWO AND THE SPEED REFERENCE OF ONE OF THE SMALLER TURBINE-GENERATORS WAS INCREASED THAT PROBABLY WOULDN'T RESULT IN THE SAME SPEED/FREQUENCY INCREASE--BUT IT WOULD CAUSE SOME INCREASE IN SPEED/FREQUENCY.

Again, these three replies are all based on the information provided AND the suppositions stated (usually in sentences written in all capital letters). It can be very difficult to answer questions like this when all of the circumstances aren't clearly stated in the problem definition. However, the physics of alternating current generation and governor speed control and generator frequency dictate that unless there are large differences in capacity between the three turbine-generators of Plant A that any single turbine-generator can be used to "match" speed/frequency and most likely even voltage for the purposes of synchronizing Plant A and Plant B. And, regardless of the capacity (rating) differences of the three turbine-generators at Plant A if they are all connected to the same bus then they are all synchronized together and all will run at the same speed/frequency.

One final note: ALL REFERENCES TO SPEED HERE ARE REFERENCES TO PERCENT OF SYNCHRONOUS SPEED. IF THE GENERATOR IS RATED AT 50% SPEED AND HAS TWO POLES, IT NEEDS TO TURN AT 3000 RPM--WHICH IS THE SYNCHRONOUS SPEED OF THE GENERATOR. THE SYNCHRONOUS SPEED OF THE GAS TURBINE COUPLED TO THE TWO-POLE GENERATOR IS THE GAS TURBINE SPEED THAT RESULTS IN 3000 RPM OF THE TWO-POLE GENERATOR IT IS COUPLED TO; THAT MIGHT BE 5134 RPM, OR 3000 RPM, OR 5129 RPM.

The fact remains--of the three turbine-generators of Plant A are all running and connected to (synchronized to) the same bus that will be synchronized to the bus of Plant B, then all three turbine-generators of Plant A are running at the same percent of synchronous speed--the SAME frequency. Changing the speed reference of one of the three turbines WILL change the speeds of all three turbines (and generators) by the same percentage--BECAUSE THEY ARE SYNCHRONIZED TOGETHER ON THE SAME BUS. MAGNETIC FORCES WILL NOT ALLOW ANY GENERATOR(S) TO OPERATE AT ANY SPEED OTHER THAN THE SPEED OF ALL THREE GENERATORS AS A GROUP.

Hope this clarifies any remaining doubts.

Note that when the speed reference of one of the turbine-generators at Plant A is changed the frequency of the loads being supplied by Plant A will also change by the same amount (as will the frequency of all three turbine-generators). Synchronism. It's a very powerful word--and a very powerful physical principle. Again, think of the frequency coming out of the electrical outlet on the wall; ALL the generators connected (SYNCHRONIZED) together are all spinning at the same speed and operating at the same frequency as the frequency of the current coming out of the electrical outlet in the wall. It can't be any other way. Period. Full stop.

Now, if the three gas turbine-generators are connected to (synchronized to) other generators and their prime movers then it will be nearly impossible to synchronize Plant A from Plant B. So, that's another supposition made for the purposes of these replies: PLANT A IS OPERATING INDEPENDENTLY OF ANY OTHER GENERATORS AND PRIME MOVERS--IT IS NOT CONNECTED TO (SYNCHRONIZED TO) ANY OTHER GENERATORS AND PRIME MOVERS WHEN TRYING TO SYNCHRONIZE (CONNECT) TO PLANT B.

I think that covers all of the perversions which might be brought up. If you have other conditions or circumstances, please try to be as specific as possible because as you read here circumstances do matter.

Best of luck! Hopefully we have answered your questions ("doubts") and provided sufficient background information and details to understand why what was written was written.
Dear Sir,
My All doubts are cleared. I will printout all your reply and read it again and again until i understand it clearly :)
. I will surely come back if any doubt in my mind. Hopefully no more doubts since you are explained every aspect of my questions. Once again thanks and really appreciated.
 
Actually, I kind of miswrote about multiple generators synchronized to a grid all operating at the "same speed." Actually, they DON'T all operate at the same speed--but they do operate at the same frequency: the frequency of the grid at any instant in time. Every synchronous generator has its synchronous speed--which is a function of the number of poles of the generator rotor (always an even number). Two pole synchronous generators operating at 50 Hz must spin at 3000 RPM; four-pole synchronous generators operating at 50 Hz must spin at 1500 Hz. Two pole synchronous generators operating at 60 Hz must spin at 3600 RPM, and four-pole synchronous generators operating at 60 Hz must spin at 1800 RPM. When a generator is UNsynchronized (not connected to/supplying any load(s)) if one increases the fuel to a gas turbine driving the generator the speed--and frequency--of the generator will increase; decrease the fuel to the gas turbine driving the generator and the frequency will decrease.

HOWEVER, when the generator is supplying a load (or loads) and IS connected to a grid with other generators and their prime movers when one increases the fuel to the gas turbine driving the generator it's speed will TRY to increase, but it won't increase very much, if at all (if it does increase, it will probably be by an imperceptible amount). On a properly regulated grid when one generator's prime mover tries to increase its speed another generator's prime mover will decrease its speed to compensate and try to maintain the grid frequency. A sudden loss of a large generator (such as when the generator breaker is tripped because of some kind of fault) will cause the grid frequency to drop by a perceptible amount--if the amount of load lost is VERY large it's very possible the grid frequency may be unstable and/or even drop so low as to cause other generators to trip, resulting in a possible black-out of the grid. But, normally increasing or decreasing the energy input into one generator's prime mover will usually have a pretty negligible effect on grid frequency overall.

Droop Speed Control is how multiple synchronous generators can all "share" in supplying multiple loads larger than any single generator could power--by acting as one large (or very large) generator, all working in harmony to produce power at a stable frequency. And do so at a stable--and singular--frequency. Droop Speed Control is how multiple generators thousands of km apart from each other can be synchronized together and produce a single, stable frequency. AND do so without any control wires connecting the plants together. Because of magnetic action/reaction and the direct relationship between speed of the generator rotor and the frequency of the generator output they can all sense what is happening and react accordingly. It really is very simple (though it seems like magic the way some textbooks and reference books and professors explain it!). It's not easy to explain or even to understand. But, once you do understand it--it really is magically simple and very, very genius.

Isochronous Speed Control, on the other hand, isn't as simple to understand. EXCEPT that there should only ever be one single generator prime mover operating in Isochronous Speed Control mode on any grid. Why? Because two--or more--generator prime movers operating in Isochronous Speed Control on the same grid will FIGHT to try control grid frequency, and the results are usually pretty ugly and involve torches (flashlights) to recover from. MANY small "grids" (also called "islands") have one generator prime mover operating in Droop Speed Control, and any other generator(s) synchronized to the same grid (island) must be operating in Droop Speed Control in order for the grid frequency to be stable. And, again, it's that character of Droop Speed Control that causes it to not try to fight other generators and their prime movers to try to control grid frequency. It will try to support grid frequency in the event it goes above or below rated frequency--but it's not going to actually return the grid frequency to nominal (rated). That's NOT Droop Speed Control's job; it can be used to do that, but that's not it's normal job.

Anyway, that's me! Over and out! Glad to have been of some help.
 
Actually, I kind of miswrote about multiple generators synchronized to a grid all operating at the "same speed." Actually, they DON'T all operate at the same speed--but they do operate at the same frequency: the frequency of the grid at any instant in time. Every synchronous generator has its synchronous speed--which is a function of the number of poles of the generator rotor (always an even number). Two pole synchronous generators operating at 50 Hz must spin at 3000 RPM; four-pole synchronous generators operating at 50 Hz must spin at 1500 Hz. Two pole synchronous generators operating at 60 Hz must spin at 3600 RPM, and four-pole synchronous generators operating at 60 Hz must spin at 1800 RPM. When a generator is UNsynchronized (not connected to/supplying any load(s)) if one increases the fuel to a gas turbine driving the generator the speed--and frequency--of the generator will increase; decrease the fuel to the gas turbine driving the generator and the frequency will decrease.

HOWEVER, when the generator is supplying a load (or loads) and IS connected to a grid with other generators and their prime movers when one increases the fuel to the gas turbine driving the generator it's speed will TRY to increase, but it won't increase very much, if at all (if it does increase, it will probably be by an imperceptible amount). On a properly regulated grid when one generator's prime mover tries to increase its speed another generator's prime mover will decrease its speed to compensate and try to maintain the grid frequency. A sudden loss of a large generator (such as when the generator breaker is tripped because of some kind of fault) will cause the grid frequency to drop by a perceptible amount--if the amount of load lost is VERY large it's very possible the grid frequency may be unstable and/or even drop so low as to cause other generators to trip, resulting in a possible black-out of the grid. But, normally increasing or decreasing the energy input into one generator's prime mover will usually have a pretty negligible effect on grid frequency overall.

Droop Speed Control is how multiple synchronous generators can all "share" in supplying multiple loads larger than any single generator could power--by acting as one large (or very large) generator, all working in harmony to produce power at a stable frequency. And do so at a stable--and singular--frequency. Droop Speed Control is how multiple generators thousands of km apart from each other can be synchronized together and produce a single, stable frequency. AND do so without any control wires connecting the plants together. Because of magnetic action/reaction and the direct relationship between speed of the generator rotor and the frequency of the generator output they can all sense what is happening and react accordingly. It really is very simple (though it seems like magic the way some textbooks and reference books and professors explain it!). It's not easy to explain or even to understand. But, once you do understand it--it really is magically simple and very, very genius.

Isochronous Speed Control, on the other hand, isn't as simple to understand. EXCEPT that there should only ever be one single generator prime mover operating in Isochronous Speed Control mode on any grid. Why? Because two--or more--generator prime movers operating in Isochronous Speed Control on the same grid will FIGHT to try control grid frequency, and the results are usually pretty ugly and involve torches (flashlights) to recover from. MANY small "grids" (also called "islands") have one generator prime mover operating in Droop Speed Control, and any other generator(s) synchronized to the same grid (island) must be operating in Droop Speed Control in order for the grid frequency to be stable. And, again, it's that character of Droop Speed Control that causes it to not try to fight other generators and their prime movers to try to control grid frequency. It will try to support grid frequency in the event it goes above or below rated frequency--but it's not going to actually return the grid frequency to nominal (rated). That's NOT Droop Speed Control's job; it can be used to do that, but that's not it's normal job.

Anyway, that's me! Over and out! Glad to have been of some help.
Dear Sir,

I read all the thread and see the scenarios below with more clarity.

- PLANT A - NORMAL CONDITION
- 3 GTGS AND RUNNING INDEPENDENTLY WITH ITS CONNECTED LOADS. NOT CONNECTED TO ANY OTHER SOURCES
- EACH GTG HAS IT OWN PMS & AVR SYSTEM
- NO CENTRALIZED PMS FOR A COMMON CONTROL
- LINK TO PLANT B IS PROVIDED TO FEED PLANT B DUE TO FAULT IN PLANT C OR PLANT C MAINTENANCE PURPOSE. A TIE-IN BREAKER IS PROVIDED BOTH PLANT A &B FOR THE THIS FUNCTION.
- ALL GTGS HAVE SAME RATING

- PLANT B - NORMAL CONDITION
- NO GENERATORS INSTALLED ON THE PLANT B
- NORMAL POWER FEED IS FROM PLANT C THOUGH A TIE-IN LINK (plant c is 50km away)
-NOT CONNECTED WITH PLANT B IN NORMAL CONDITION
- A LINK IS PROVIDED WITH PLANT A WITH SYNCHRONIZING FACILITY AT PLANT B IN CASE REQUIRED

- PLANT C - NORMAL CONDITION
- 6 GTS RUNNING AND FEEDING PLANT C LOADS. ADDITIONALLY FEEDING PLANT B
- PLANT C & A GTGS ARE NOT RUNNING IN PARALLEL IN NORMAL CONDITION
- ALL GTGS AT PLANT C ARE SAME RATING
- NO OTHER GRID OR GENERATORS ARE CONNECTED TO PLANT C

REQUIREMENT:[IN CASE OF EMERGENCY]
- 3 GTGS ARE RUNNING IN PARALLEL AND READY TO FEED PLANT B
- PLANT A, B & C RUNNING CONTINUOUSLY WITH ITS OWN LOADS
- PLANT C REQUIRED SOME MAINTENANCE AND NEED TO OPEN THE POWER FEED TO PLANT B
- PLANT B NOW NEED TO POWERED FROM PLANT A
- PLANT, A, B & C RUNNING LOADS SHOULD NOT AFFECT DURING THIS POWER TRANSFER
- AFTER A SHORT PERIOD OF PARALLELING WITH PLANT A, PLANT C SHOULD BE OPEN AND PLANT B TO BE RUNNING WITH PLANT A
- ONCE THE PLANNED MAINTENANCE AT PLANT C IS COMPLETED, PLANT B WILL BE REMOVED FROM PLANT A AND NEED TO CONNECT BACK TO PLANT C
- PLANT C IS IN REMOTE AND NOT POSSIBLE TO ADJUST GTG PARAMETERS FOR SHORT TIME SYNCHRONISATION WITH PLANT A.

MY UNDERSTANDING:
- DURING THIS POWER TRANSFER FROM PLANT A TO B, 3 GTGS IN PLANT B TO BE SET IN DROOP MODE.
- PLANT C POWER IS ALREADY AVAILABLE AT PLANT B .
- ADJUST THE FREQUECY OF ANY ONE ONE OF THE GTG AT PLANT A SLIGHTLY ABOVE THE PLANT C FREQUENCY
- ADJUST THE VOLTAGE OF THE ANY ONE OF THE GTG AT PLANT A SLIGHTLY ABOVE THE PLANT C VOLTAGE.
- IF WE CHANGE FREQUENCY OF ONE DROOP GENRATOR OF PLANT A, OTHER TWO GENERATORS WILL FOLLOW THE SAME FREQUENCY
- - SYNCHRONIZE BOTH PLANT A & C GTGS ONCE THE PHASE ANGLE, VOLTAGE AND FREQUENCY ARE WITH IN THE RANGE USING SYNCHRONIZE AT PLANT B.
- ALL THESE OPERATIONS CAN BE DONE FROM PLANT B.
- ONCE ALL GTGS ARE SYNCHRONISED, TRANSFER THE LOAD OF PLANT B FROM PLANT C TO PLANT A
- OPEN THE TIE-IN BREAKER OF PLANT C

- REPEAT THE SAME WHEN TRANSFER BACK THE LOAD TO PLANT C

MY DOUBTS:

- DURING THE SHORT PARALLEL OPERATION WITH PLANT A & C, LOAD OF PLANT A , B AND C WILL BE SHARED BETWEEN ALL 8 OR 9 GTGS???
- HOW WE WILL SMOOTHLY TRANSFER THE PLANT B LOAD TO PLANT A FROM PLANT C. NEED TO ADJUST FREQUECY, mw, pf ETC. OF PLANT A GTGS?
- IS THERE ANY POSSIBLE TECHNICAL ISSUE FOR A BUMP LESS POWER TRANSFER SINCE THERE IS NO MASTER POWER MANAGEMENT SYSTEM AT PLANT A TO CONTROL ALL GTGS TOGETHER?

Once again thank you for your valuable time... This is only for improving my own knowledge..... Please give a reply if your time permits. Hope i gave enough clarifications for the requirements

regards
 
WOW! This is really getting crazy.

Are those really doubts? Or just questions...???

I REALLY don't get the whole Plant B and Plant C relationship at all.

If Plant B doesn't have any generators, where does it get power from to supply the loads connected to Plant B?

Any time multiple generators are connected to a common "line" they are synchronized together, operating at the same frequency. Can't be any other way.

If Plant A is producing 60 MW out of a possible 90 MW (meaning each of the turbines is capable of producing 30 MW), and is connected (synchronized) to Plant B while all of the turbine-generators are running on Droop Speed Control then the total output of Plant A is going to remain at 60 MW at the instant of synchronization and until someone issues a RAISE- or LOWER SPEED/LOAD command to one or more of the units.

If Plant C is connected to Plant B when Plant A is synchronized to Plant B and all of Plant C's turbine-generators are running on Droop Speed Control and producing 100 MW (out of a possible 150 MW) Plant C will continue to produce 100 MW, and Plant A will continue to produce 60 MW at the instant of synchronization and until someone issues a RAISE- or LOWER SPEED/LOAD command to one or more of the units. This is all supposing that there was very little difference, if any, in the frequency of Plant A and Plant C. I STILL don't know where Plant B is getting its power from and what loads it is supplying...!

Further, when Plant A is connected to Plant B and Plant C, all of the turbine-generators are Plants A & -C are operating in parallel with each other AND with the units providing power to Plant B!!! Since they would all be connected to the same "line" at that point.

If you tried simply increasing the power output of Plant A from Plant B what would happen would be that the frequency would tend to increase--this is supposing that Plant B is getting power from a plant or plants or grid elsewhere. And, if those machines didn't decrease their output by an equal amount then the frequency would tend to increase. (It's most likely the other generators and their prime movers supplying Plant B with power are also operating on Droop Speed Control mode--so they would sense the change in frequency and decrease their output to try to support the grid.)

This is all getting very confusing--and is just a what-if, twenty questions game. I can't think of a real world scenario where something like this would ever be necessary. Bumpless transfer? As you have drawn it, and with the additional information you have provided? No. Emphatically no.

NOTE: Underlined text in red are modifications to the original response to enhance clarity.
 
Sorry for the mis-understanding due to my SLD. This is for my own study and PLANT A is not a real installed scenario.. Just curious to know how it will work if connected this way.
Plant A & B considered both have synchronizing facility.
Plant A should be continuously working with its own loads and Plant C also continuously working with its ownload but with Plant B loads. Plat A & C will never working in parallel in normal operation and need to do momentary paralleling in case plant A need to supply Power to Plant B . Actually here, there is no grid .. I wrongly mention Plant C as Grid. Sorry for that.

I am not an expert on the generator control and my understanding is 3 GTGs on plant A will set in droop mode and adjust the Voltage and frequency from Plant B then it will momentary synchronize with Plant C generators. Once it is synchronized, Plant C breaker to Plant B will be open. Then plant C can do their planned maintenance. My question was is it Easy to do synchronization when 3 GTS are running at Plant A with Plant C Generators to feed power to Plant B from A.

Thank you very much for your time for explanation .

regards
At least you confirmed presence of TIE IN CB..
The point is that the scenarios that you presented here are still not clear ..

Cheers
James
 
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