Why using bleed valve's at lower power generation?

Hi there,

Bleed valves used within Gasturbines like GE are taking precautions against Ice - stall (surge), … at starting up moments or stopping.
But why do they use the bleed valves out these periods - we also see that this happens at a certain time in production mode - lower power at same speed ref.
Please advice.

Kind regards HoltW
 
Hi Holtw

There is some very good threads on this forum explaining the operations and benefits for IBH on GT .

I strongly advise you to have a look on them.

There is surely the right answer for your response ,

Regards,
James
 
HoltW,

GE designs and manufactures many different gas turbines, which fall into two basic groups: heavy duty gas turbine and aero-derivative gas turbines (aircraft engine gas generators with power turbines attached for land-based applications). Both some kind of "bleed valve" but they can take several different forms.

In general, "bleed valves" (I'm specifically referring to axial compressor bleed valves) are used primarily for protection against stalls or surges during low-speed operation during starting or shutdown--not low power operation. (I'm defining low power operation as AC power generation at low power output (low load AC power generation); whereas I'm defining low-speed operation as turbine/compressor operation during starting and shutdown at less than rated speed. AC power generation occurs at rated speed (when the frequency is at rated also).) I have seen some aero-derivative gas turbines that use bleed valves for anti-icing protection, but mostly in aircraft applications, not so much in land-based applications (AC power generation; mechanical drive applications (process compressors or pumps, etc.).

Heavy duty gas turbines typically have the axial compressor bleed valves open during starting and shutdown (low speed or part speed operation); some heavy duty gas turbines keep the axial compressor bleed valves open for a short time after reaching rated speed and during low power generation periods (say, 5 MW or less). Again this is usually done when the air flow through the axial compressor of the unit is at or near less than design conditions to protect the axial compressor from stalling or surging (which can be very destructive to the axial compressor). Most of these types of axial compressor bleed valves are connected to mid-axial compressor taps (for example, the 7th stage, or 9th-, 10th or 11th stages of the axial compressor). They are open to reduce the amount of air that is flowing through the axial compressor by directing some of the air flow to the turbine exhaust area--again during starting or stopping. This is because axial compressors are designed to operate at rated speed, but during starting and stopping they have to accelerate from zero speed or decelerate to zero speed--necessitating the need for reducing air flow to prevent compressor stalling or surging. (Axial compressors are a very different type of machine from centrifugal compressors or piston-type compressors and have very unique characteristics. They are excellent at moving LOTS of air at rated speed, but they are not so good at moving air at low (part) speed operation and need protection--which the axial compressor bleed valves provide.)

In my own personal experience, axial compressor bleed valves on heavy duty gas turbines are not used for anti-icing functions. Some GE-design heavy duty gas turbines have variable valves which can extract ("bleed") a portion of the axial compressor discharge air (from the discharge of the axial compressor, but not from intermediate stages of the axial compressor) and recirculate it to help prevent icing at the axial compressor inlet, or to protect the compressor when the variable axial compressor inlet guide vanes are closed to very low angles (air flows).)

Hope this helps! Again, there are different types of gas turbines (heavy duty and aero-derivative), and there are different types of "bleed" (extraction) valves. And, the purposes of each, and the times when they are used (opened) are also different, as are the reasons for opening the valves (because they are usually closed during normal operation at rated speed at rated operating conditions)

.
 
Hi Guys,

Thanks for the intell, I knew what it does at start stop, but my guestion goes more specifically at the point where the power ramps at his 'lowest' power ratings. It happens that when we go from 350MW to about 100MW or les, then at this lowest point the bleed valve opens for a certain timelaps. So correct me if I'm wrong, I suppose for these lower ratings they do not want to risk a stall/surge operating?

It's my best guess ...
 
HoltW,

All gas turbines are not alike, not even all GE-design gas turbines--be they heavy duty or aero-derivative. And, when it comes to the differences between F-class (including FA and FB) and B/E-class units (the original workhorses of the GE fleet of heavy duty gas turbines) they (the differences) can be great. Yes; they all suck, squeeze, burn and blow (draw air into the axial compressor; compress it; add fuel to the compressed air and burn the fuel; and exhaust to atmosphere or an HRSG ("boiler") or possibly to some other process)--but often-times the similarities end there.

So, when you're asking about a specific process or point in the process and a specific machine, please--be specific about the machine and the process or point in the process.

And for the record, 100 MW out of 350 MW isn't really "low power" (not in many people's estimation; and as a percentage it's more than 28.5% of the rated power you listed, not exactly "low power").

If the unit you are asking about has DLN combustors AND the unit is being unloaded very quickly, not at some normal rate of say 1 MW/sec or thereabouts, then it's possible the designers of the unit have decided to use the axial compressor bleed valves to help protect the axial compressor against stalling or surging if the IGVs are also closed very quickly while the unit is at rated speed. Again, axial compressors are really unique machines all by themselves, and the manufacturers and designers of large heavy duty gas turbines are doing some very unique and unusual things to maximize air flow through the machine (so the power output of the machine can be optimized and maximized under normal operating conditions) and that may include using the axial compressor bleed valves in some fashion.

You haven't told of the axial compressor bleed valves on the unit you are asking about are "bang-bang" bleed valves (meaning they are either fully closed or fully open--and don't move or can't be moved to some intermediate position), or if they are modulated bleed valves with some type of actuator/positioning device that can move the bleed valve to some number of or any number of intermediate positions as necessary).

In decades past (or is it passed ...???), modulating axial compressor bleed valves was not typically done on GE-design heavy duty gas turbines. For several reasons, but mostly for two reasons: it wasn't necessary, and it was costly. As the machines have become more sophisticated (and, too, the control systems!) and the desire to maximize power and efficiency and yet try to maintain operability it has become more necessary to devise and implement new and different control schemes. And, as control systems have become more sophisticated and more capable, including actuators, new control (and protection) schemes have become the norm.

So, when you're asking what seems like a simple and general question--please don't assume that all gas turbines, of any manufacturer, are alike in all or most respects. It's just not true. And if you're fortunate enough to be working on a machine that was manufactured and/or designed by GE in Belfort, France, you can be assured they have pulled out all the stops on implementing new and untried and untested control (and protection) schemes, all in a conscious effort to maximize complexity at the expense of simplicity and operability. They do seem to do a little better job of documenting some (but not all!) of their schemes, so do have a look at the Operations and Service Manuals provided with the unit for information (one should always RTFM (Read The Fine Manual) when trying to understand a unit or its control and protection schemes).

Best of luck!
 
Hi CSA,

Thx for the intell. I've already took a better look at the Original manuals, but some thing have been changed the last few years. The turbine is a FA type of GE9 and also like you've said DLN. I'll take some new approche to the system operating to clear up some things. When I know some new specific elements I'll keep in tough.
Nevertheless, I'ts good to hear some people to know the skills about these magnificant machines. And yes indeed it's not Always black and white like you've said before. There are at other plants GT from different manufactures and like Siemens or RR. Let's say we have a GT with 2 different pressure modes, HP en LP compressors at one GT. So it's not correct to say it's the same thing.
My apologies for the inconvenience about the simple question that may lead to a simple question, that rather would be better to a specifically question. The same if I would ask how big a inductance is 1H, not knowing, in air-core material-amps, ...
However, I'ts a good practice and hopefully could lead us to a better understanding.

Kind regards,

HOLTW
 
[/They are open to reduce the amount of air that is flowing through the axial compressor by directing some of the air flow to the turbine exhaust area--again during starting or stopping.]

Dear CSA i dont understood something, the compressor enter in surge conditions when is in low air flow so a portion of the discharge is directed to the suction to increase the flow and then scape from the low flow that causes surge, but you say that the valves reduces the air flow, wich is the opposite that we want....am i wrong?
1595794829860.png
 
This discussion was about GE-design heavy duty gas turbine axial compressor during starting and stopping--meaning below rated speed.

Your question and graph are not clear. Is the question about axial compressors or centrifugal compressors? Above or below rated speed?

I AM NOT any kind of expert (even a novice one) on surge/stall of either axial or centrifugal compressors. I only know what I've read and what I've experienced. The maths of surge/stall is beyond my abilities, and I'm too old to start relearning the maths necessary to understand the topic well enough to be able to explain it to anyone else so they can understand it.

Perhaps if you fully detail your question properly--and if it's not related to GE-design heavy duty gas turbine axial compressors--ask the question in a new thread you may receive a satisfactory answer.

Best of luck!!!
 
dear CSA my apologies if i was unclear with the question i will try to do it again.
and for the record I am not an expert, not in compressor, not in combustion, not in control I AM only a begginer who is triying to improve to make my job with no mistakes (operator in a combined cycle) and I learn a LOT....a LOT reading your posts (thank you so much)
my question was related to an axial compressor GE design for a 9FA GT in operation below rated speed, for my understanding the surge begins when the flow trough the compressor is low so a portion of the discharge is redirected to the suction to increase that flow and thay way avoid the low flow conditions. its that correct?
in our plant we have some anti-surge valves (who dont redirect the to the suction, they redirect to the exhaust) and we have IBH
its both system necesessary?

best regards
 
ratm,

You need to understand and internalize something very important about F-class (and FA-class) GE-design heavy duty gas turbines: They were designed to be Base Load machines and they were NOT designed to be operated off-frequency. Off-frequency operation is one of the most common causes of all manner of failures of these machines and their components--especially compressors and IGVs. There are literally at least a dozen different versions of compressors and IGVs and stator vanes and exit guide vanes and ... and ... for F-class (and FA-class) machines, all primarily intended to help reduce issues caused by off-frequency operation.

As was said in the other thread you opened about IBH and liquid fuel--IBH on a F/FA-class machine is different than on other machines. And if you have some unusual or "odd" anti-surge valves--they are totally on GE Belfort to explain and/or detail. Again, I would have to guess they are also intended to help with off-frequency operation. I don't believe that ANYONE at GE when the F/FA-class machines were designed and initially built expected them to EVER be employed in parts of the world where off-frequency operation was the norm rather than the exception. EVER. As in NEVER.

If you've been following the development of the HA-class machines, it certainly seems like with all of the off-frequency testing (and the test stands designed specifically to test off-frequency operation) they were designed with off-frequency operation in mind as the norm rather than the exception. (Why? Because of all the issues, specifically with GE-design Frame 9 F/FA-class heavy duty gas turbine problems related specifically to off-frequency operation! NO ONE wanted to go through this EVER again with a new class of gas turbine.)

I simply cannot and will not try to address what is or may have been done by GE Belfort to machines to try to mitigate the effects of off-frequency operation.

Lastly, I--as a rational, thinking human being--simply cannot fathom why certain parts of the world simply continue to put up with and endure off-frequency operation. It's ... insane (among other more descriptive and more offensive terms which could be used to describe the continued practice). Fix the problem; it's not rocket science. Make people pay for the electricity they use, and usage will decrease--probably to a level that would allow a stable grid, or at least a more stable grid--and from there as new generation is added things will get better. Maybe even to the point that electricity theft could once again be tolerated (though probably not to the same level as now). It's just irrational to keep fighting this problem from the supply side--there isn't enough money to do this at this time.

Sorry. There's a right way and a wrong way to go about problem-solving. And politics messes things up every damn time. And when large blocks of generation are taken off-line because of problems caused by off-frequency operation it just seems that the off-frequency problem is worsened. Use machines the way they were intended. Distribute electricity the way it was intended. (I know; I didn't grow up in a part of the world where electricity was a luxury or where it was rationed or where it was unobtainable (because of cost or distribution issues). Electricity is a commodity, and commodities cost money.
 
dear SCA i think i messed up again trying to formulate the question when i said .." in operation below rated speed " I meant in the start-up and shutdown process...not that we use the machine off-grid ...we ussually are in base load on-grid...we are not savages jaja

best regards
 
Base Load, on grid in some parts of the world is pretty synonymous with off-frequency operation.

Look, all I know about starting and shutting down below rated speed is that the axial compressor is very prone to have serious stall/surge without "diverting" a portion of the air flow through the compressor. And, on GE-design heavy duty gas turbines, the compressor bleed valves (operated by solenoid(s) 20CB-n) are how the air flow is diverted from mid-stream locations in the axial compressor to the exhaust during acceleration and deceleration to and from rated speed when the generator breaker is not closed. I ain't no maths expert, and all I know is that if the compressor bleed valves aren't open during starting/acceleration and shutdown/deceleration a whole lot of shaking goes on--meaning high vibration (HIGH-HIGH vibration) and in some cases the compressor can be severely damaged. That's why the unit cannot be started unless all of the compressor bleed valves are fully open, and if any one of them closes during starting/acceleration the unit gets tripped. And, during shutdown/deceleration if the compressor bleed valves don't open fully--all of them--the unit will be tripped (meaning fuel will be immediately shut off). They are important. Most heavy duty, and even aircraft engines and aircraft-derivative engines, use some kind of "bleed valve" (some have very different names: pop-off valves, for example) to get through the regions of speed where the axial compressor is vulnerable to serious problems. Some are solenoid-operated; some are spring-loaded and open when the pressure gets higher than spring tension.

Axial compressors are unique machines with unique operating characteristics. Best to leave the control and protection to the maths and compressor design experts.

You have demonstrated you're not a savage; you know how to use the Internet. NO ONE who can use the Internet is a savage.
 
ratm,

Axial compressors are designed to operate (continuously; at rated performance) in a very small range of speed. However, the turbine which drives the axial compressor on a single-shaft gas turbine has to be accelerated from zero speed to that speed range. (For many single-shaft heavy duty gas turbines which drive synchronous generators the rated speed is actually synonymous with the generator's synchronous speed, and often that includes turbines (and their axial compressors) that are coupled to the generator through a reduction gear.)

As was mentioned, axial compressors are unique machines, and accelerating them up to rated speed means they are prone to experience speed ranges where sometimes the flow of air from one stage to the next is "interrupted"--meaning that the flow of air stalls, usually because the air flow can't overcome the pressure of the downstream stage (as I understand it, and my understanding isn't all that great).

SO, the designers of axial compressors develop ways to divert some of the air flow, usually to the exhaust of the gas turbine, in order to alleviate the air flow problems and allow the compressor to accelerate through the condition without causing high vibration, or compressor damage. For GE-design heavy duty gas turbines, the method chosen was to use axial compressor bleed valves (that was the name chosen for the valves. It just means a valve that, when open, diverts air from some stage(s) of the axial compressor during acceleration to and deceleration from rated speed. "Bleed" is a term which generally means "to extract", and by extracting a portion of the air flow between axial compressor stages--and diverting it to some innocuous area (such as the gas turbine exhaust (because the extracted air is usually hotter than ambient and if just diverted to atmosphere it can also be noisy)--the axial compressor is protected from high vibration and damage during acceleration and deceleration.

I understand that some newer designs of GE Frame 9 F/FA heavy duty gas turbine axial compressors employ additional means of reducing air flows through the axial compressor at certain operating conditions--such as fast load reduction, especially when the unit is operating off-frequency (meaning the generator breaker is closed, the unit is connected to a grid and the grid frequency is (usually) below rated, sometimes "significantly" below rated (less than 48 Hz or so) and for prolonged periods of time. Additionally, some of these grids experience large and fast swings of frequency and since the turbine-generator speed is controlled by grid frequency--meaning the axial compressor speed is controlled by grid frequency--well, things can get messy and there are times when things happen which can't be understood or explained, usually resulting in serious damage to the machine (meaning the axial compressor).

There are even new axial compressor sections which are being installed on some machine which have multiple stages of variable stator vanes--like are commonly seen on aircraft gas turbine engines. The stages of variable stator vanes are linked together and moved by a hydraulic (sometimes electric) actuator as load changes--and as speed changes. Myself, I haven't had the "pleasure" of working on one of these machines during commissioning so I haven't been able to analyze the control and protection schemes used to these new variable stator vane designs.

The thing operators need to know about the axial compressor bleed valves is this: During starting and stopping when the unit is accelerating to or decelerating from rated speed the axial compressor bleed valves MUST be open, and by open it means the fully open limit switches on each valve must indicate the valves are fully open. The valves are normally open, with very large springs to move them to the fully open position. Usually, compressed air (dry instrument air for many units) is used to close the axial compressor bleed valves once the unit reaches rated speed. Some units don't close the axial compressor bleed valves until the unit has been synchronized and some "small" amount of load has been accepted from the grid. Sometimes, the axial compressor bleed valves will be opened during shutdown as the load reaches a "small" amount while unloading (before the generator breaker opens). It all kind of depends on the type of combustion system and the division of GE that is programming the turbine control system.

I can't speak to any other valves used to extract (divert; "bleed") air from intermediate axial compressor stages during loaded operation--I haven't seen them, worked on them, or commissioned them. I can say that I would expect the programming and configuration of such valves has been tested and confirmed to serve the protection functions at the time of operation. Having said that, I want to re-iterate something about F/FA-class GE-design heavy duty gas turbines: They were designed to be operated at Base Load for extended periods of time and at rated speed on well-regulated grids. That's a fact. Full stop. Period. A LOT of GE-design F/FA-class heavy duty gas turbines have been sold, installed, commissioned and are now being operated in dispatched applications--meaning they start and stop, sometimes twice a day, and don't always operate at Base Load when they are running. AND, they are widely used in parts of the world where the grid frequency is ..., well, ..., less than optimal. (Not quite at savage levels, but certainly not desirable or even optimal. And, for periods that can be several minutes, or even longer.) Now, because these machines all have axial compressors--which were designed to operate at a particular speed (not even a narrow or small speed range--but a particular speed) unusual things happen. Now, throw a very complicated combustion system (DLN 2.6 or 2.6+ or 2.6e or 2.6+e) which is trying to maintain premix flame AND emissions all while the air flows are less than rated AND fluctuating as grid frequency (and turbine speed) fluctuate and you have a recipe for unusual things to happen.

So, some divisions of GE (think GE Belfort) have decided to try various methods and schemes to try to protect axial compressors and maintain DLN combustion AND exhaust emissions all while the grid frequency is not normal, usually less than rated. On machines that weren't designed to be operated at less than rated speed (meaning the axial compressors in particular). AND, the speed can change very quickly (as grid frequency changes--sometimes very quickly).

This is one thing a LOT of people don't understand about AC power generation. Speed and frequency are directly related. And, when a prime move and synchronous generator are synchronized to a large or infinite grid with many other prime movers and generators the grid frequency controls the unit speeds. Not the governors (control systems; turbine control systems)==the grid frequency. Why? The magnetic forces at work inside the synchronous generators dictate (in a very authoritarian way!) the speed of the generator rotor WILL BE proportional to the grid frequency. Period. Full Stop. No if's. No and's. No butt's. (F=(P*N)/120) is the law. People believe that when the grid is experiencing frequency problems THEIR machine should be stable (meaning the power output AND the speed (frequency) should be rock-solid, regardless of the grid frequency. BUT, that just isn't so--and it will never be so. And it reflects a very serious misunderstanding of basic AC power generation.

Anyway, see how this is all interconnected? We all have to remember (even turbine and axial compressor designers--and turbine-generator salespeople) that the objective is to produce electricity--AC (Alternating Current) electricity. And one of the things about AC power generator and distribution is that is assumed to be at a relatively stable (constant) frequency. (That's the idea anyway...) The machines which drive (supply torque to) the synchronous generators have to be designed and applied to meet the requirements and conditions of the grids where they will be installed and operated. I just don't think anyone expected so many F/FA-class machines to be installed in areas where the grid frequency was an unstable as it is and can be. AND, I believe that any people believed that by installing some of these large F/FA-class machines the grids would become more stable. But, that hasn't automatically happened. And, if we continue down this particular rabbit-hole we are going to get further away from you questions about axial compressor bleed valves.

Later!
 
ratm,

Axial compressors are designed to operate (continuously; at rated performance) in a very small range of speed. However, the turbine which drives the axial compressor on a single-shaft gas turbine has to be accelerated from zero speed to that speed range. (For many single-shaft heavy duty gas turbines which drive synchronous generators the rated speed is actually synonymous with the generator's synchronous speed, and often that includes turbines (and their axial compressors) that are coupled to the generator through a reduction gear.)

As was mentioned, axial compressors are unique machines, and accelerating them up to rated speed means they are prone to experience speed ranges where sometimes the flow of air from one stage to the next is "interrupted"--meaning that the flow of air stalls, usually because the air flow can't overcome the pressure of the downstream stage (as I understand it, and my understanding isn't all that great).

SO, the designers of axial compressors develop ways to divert some of the air flow, usually to the exhaust of the gas turbine, in order to alleviate the air flow problems and allow the compressor to accelerate through the condition without causing high vibration, or compressor damage. For GE-design heavy duty gas turbines, the method chosen was to use axial compressor bleed valves (that was the name chosen for the valves. It just means a valve that, when open, diverts air from some stage(s) of the axial compressor during acceleration to and deceleration from rated speed. "Bleed" is a term which generally means "to extract", and by extracting a portion of the air flow between axial compressor stages--and diverting it to some innocuous area (such as the gas turbine exhaust (because the extracted air is usually hotter than ambient and if just diverted to atmosphere it can also be noisy)--the axial compressor is protected from high vibration and damage during acceleration and deceleration.

I understand that some newer designs of GE Frame 9 F/FA heavy duty gas turbine axial compressors employ additional means of reducing air flows through the axial compressor at certain operating conditions--such as fast load reduction, especially when the unit is operating off-frequency (meaning the generator breaker is closed, the unit is connected to a grid and the grid frequency is (usually) below rated, sometimes "significantly" below rated (less than 48 Hz or so) and for prolonged periods of time. Additionally, some of these grids experience large and fast swings of frequency and since the turbine-generator speed is controlled by grid frequency--meaning the axial compressor speed is controlled by grid frequency--well, things can get messy and there are times when things happen which can't be understood or explained, usually resulting in serious damage to the machine (meaning the axial compressor).

There are even new axial compressor sections which are being installed on some machine which have multiple stages of variable stator vanes--like are commonly seen on aircraft gas turbine engines. The stages of variable stator vanes are linked together and moved by a hydraulic (sometimes electric) actuator as load changes--and as speed changes. Myself, I haven't had the "pleasure" of working on one of these machines during commissioning so I haven't been able to analyze the control and protection schemes used to these new variable stator vane designs.

The thing operators need to know about the axial compressor bleed valves is this: During starting and stopping when the unit is accelerating to or decelerating from rated speed the axial compressor bleed valves MUST be open, and by open it means the fully open limit switches on each valve must indicate the valves are fully open. The valves are normally open, with very large springs to move them to the fully open position. Usually, compressed air (dry instrument air for many units) is used to close the axial compressor bleed valves once the unit reaches rated speed. Some units don't close the axial compressor bleed valves until the unit has been synchronized and some "small" amount of load has been accepted from the grid. Sometimes, the axial compressor bleed valves will be opened during shutdown as the load reaches a "small" amount while unloading (before the generator breaker opens). It all kind of depends on the type of combustion system and the division of GE that is programming the turbine control system.

I can't speak to any other valves used to extract (divert; "bleed") air from intermediate axial compressor stages during loaded operation--I haven't seen them, worked on them, or commissioned them. I can say that I would expect the programming and configuration of such valves has been tested and confirmed to serve the protection functions at the time of operation. Having said that, I want to re-iterate something about F/FA-class GE-design heavy duty gas turbines: They were designed to be operated at Base Load for extended periods of time and at rated speed on well-regulated grids. That's a fact. Full stop. Period. A LOT of GE-design F/FA-class heavy duty gas turbines have been sold, installed, commissioned and are now being operated in dispatched applications--meaning they start and stop, sometimes twice a day, and don't always operate at Base Load when they are running. AND, they are widely used in parts of the world where the grid frequency is ..., well, ..., less than optimal. (Not quite at savage levels, but certainly not desirable or even optimal. And, for periods that can be several minutes, or even longer.) Now, because these machines all have axial compressors--which were designed to operate at a particular speed (not even a narrow or small speed range--but a particular speed) unusual things happen. Now, throw a very complicated combustion system (DLN 2.6 or 2.6+ or 2.6e or 2.6+e) which is trying to maintain premix flame AND emissions all while the air flows are less than rated AND fluctuating as grid frequency (and turbine speed) fluctuate and you have a recipe for unusual things to happen.

So, some divisions of GE (think GE Belfort) have decided to try various methods and schemes to try to protect axial compressors and maintain DLN combustion AND exhaust emissions all while the grid frequency is not normal, usually less than rated. On machines that weren't designed to be operated at less than rated speed (meaning the axial compressors in particular). AND, the speed can change very quickly (as grid frequency changes--sometimes very quickly).

This is one thing a LOT of people don't understand about AC power generation. Speed and frequency are directly related. And, when a prime move and synchronous generator are synchronized to a large or infinite grid with many other prime movers and generators the grid frequency controls the unit speeds. Not the governors (control systems; turbine control systems)==the grid frequency. Why? The magnetic forces at work inside the synchronous generators dictate (in a very authoritarian way!) the speed of the generator rotor WILL BE proportional to the grid frequency. Period. Full Stop. No if's. No and's. No butt's. (F=(P*N)/120) is the law. People believe that when the grid is experiencing frequency problems THEIR machine should be stable (meaning the power output AND the speed (frequency) should be rock-solid, regardless of the grid frequency. BUT, that just isn't so--and it will never be so. And it reflects a very serious misunderstanding of basic AC power generation.

Anyway, see how this is all interconnected? We all have to remember (even turbine and axial compressor designers--and turbine-generator salespeople) that the objective is to produce electricity--AC (Alternating Current) electricity. And one of the things about AC power generator and distribution is that is assumed to be at a relatively stable (constant) frequency. (That's the idea anyway...) The machines which drive (supply torque to) the synchronous generators have to be designed and applied to meet the requirements and conditions of the grids where they will be installed and operated. I just don't think anyone expected so many F/FA-class machines to be installed in areas where the grid frequency was an unstable as it is and can be. AND, I believe that any people believed that by installing some of these large F/FA-class machines the grids would become more stable. But, that hasn't automatically happened. And, if we continue down this particular rabbit-hole we are going to get further away from you questions about axial compressor bleed valves.

Later!
SCA nothing to add, you said it all , gracias!!!
 
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