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from the Maintenance department...
Govenor Control
Could anyone please explain the two above systems and there differnces or refer me to some text that will
Regards
Scott_F
Regards
Scott_F
In a nutshell, Isochronous Speed Control refers to the prime mover governor speed control mode that controls the frequency (speed) of an AC generator (alternator) and Droop Speed Control refers to the prime mover governor speed control mode that allows multiple AC generators (alternators) to be operated in parallel with each other to power large electrical loads, or to "share" load.
The frequency of a synchronous AC generator (the type most commonly used in AC power generation) is directly proportional to the speed of the rotating electrical field(s) F = P * N / 120, where F = frequency (in Hz), P = number of poles of the rotating electrical field, and N = the speed of the rotating electrical field (in RPM).
In Isochoronous Speed Control mode, the energy being admitted to the prime mover is regulated very tightly in response to changes in load which would tend to cause changes in frequency (speed). Any increase in load would tend to cause the frequency to decrease, but energy is quickly admitted to the the prime mover to maintain the frequency at the setpoint. Any decrease in load would tend to cause the frequency to increase, but energy is quickly reduced to the prime mover to maintain the frequency at the setpoint.
In Droop Speed Control mode, the governor of the prime mover is not attempting to control the frequency (speed) of the AC generator. The term "share the load" causes much confusion, but just refers to the ability of the prime movers of AC generators to smoothly control the production of torque when connected in parallel with other generators supplying an electrical load.
Droop Speed Control, in fact, refers to the fact that the energy being admitted to the prime mover of the AC generator is being controlled in response to the difference between a speed (frequency) setpoint and the actual speed (frequency) of the prime mover. To increase the power output of the generator, the operator increases the speed setpoint of the prime mover, but since the speed cannot change (it's fixed by the frequency of the grid to which the generator is connected) the error, or difference, is used to increase the energy being admitted to the prime mover. So, the actual speed is being "allowed" to "droop" below its setpoint.
On a small electrical grid, one machine is usually operated in Isochronous Speed Control mode, and any other (usually smaller) generators which are connected to the grid are operated in Droop Speed Control mode. If two prime movers operating in Isochronous Speed Control mode are connected to the same electrical grid, they will usually "fight" to control the frequency, and wild oscillations of the grid frequency usually result. Only one machine can have its governor operating in Isochronous Speed Control mode for stable grid frequency control when multiple units are being operated in parallel. (There are Isochronous Load Sharing schemes in use in various places around the world, but they aren't very common.)
On very large electrical grids--commonly referred to as "infinite" electrical grids--there is no single machine operating in Isochronous Speed Control Mode which is capable of controlling the grid frequency; all the prime movers are being operated in Droop Speed Control mode. But there are so many of them and the electrical grid is so large that no single unit can cause the grid frequency to increase or decrease by more than a few hundredths of a percent as it is loaded or unloaded.
Very large electrical grids require system operators to quickly respond to changes in load in order to control grid frequency properly since there is no Isochronous machine doing so. Usually, when things are operating normally, changes in load can be anticipated and additional generation can be added or subtracted in order to maintain tight frequency control.
One method many electrical grid operators use to control grid frequency is called AGC, or Automatic Grid Control. Units being operated in AGC get their Droop Speed Control speed setpoints adjusted remotely in response to commands from the system operator(s) to maintain grid frequency.
There really is a dearth of material on Droop and Isochronous governor control, and much of what is written is very difficult to understand and, frankly, is explained in unrealistic terms. One of the best authors on the subject is Charles I. Hubert; his 'Preventive Maintenance of Electrical Equipment' and 'Electric Machines: Theory, Operation, Applications, Adjustment, and Control' both contain some good sections (though brief) on the two speed governor control modes.
This author is hopeful that someday soon, an article on Wikipedia will be started and that the collective thoughts and efforts of many knowledgeable people will be combined into one thoughtful and insightful-and most importantly, understandable--definition of the concept of governor speed control modes.
markvguy
The frequency of a synchronous AC generator (the type most commonly used in AC power generation) is directly proportional to the speed of the rotating electrical field(s) F = P * N / 120, where F = frequency (in Hz), P = number of poles of the rotating electrical field, and N = the speed of the rotating electrical field (in RPM).
In Isochoronous Speed Control mode, the energy being admitted to the prime mover is regulated very tightly in response to changes in load which would tend to cause changes in frequency (speed). Any increase in load would tend to cause the frequency to decrease, but energy is quickly admitted to the the prime mover to maintain the frequency at the setpoint. Any decrease in load would tend to cause the frequency to increase, but energy is quickly reduced to the prime mover to maintain the frequency at the setpoint.
In Droop Speed Control mode, the governor of the prime mover is not attempting to control the frequency (speed) of the AC generator. The term "share the load" causes much confusion, but just refers to the ability of the prime movers of AC generators to smoothly control the production of torque when connected in parallel with other generators supplying an electrical load.
Droop Speed Control, in fact, refers to the fact that the energy being admitted to the prime mover of the AC generator is being controlled in response to the difference between a speed (frequency) setpoint and the actual speed (frequency) of the prime mover. To increase the power output of the generator, the operator increases the speed setpoint of the prime mover, but since the speed cannot change (it's fixed by the frequency of the grid to which the generator is connected) the error, or difference, is used to increase the energy being admitted to the prime mover. So, the actual speed is being "allowed" to "droop" below its setpoint.
On a small electrical grid, one machine is usually operated in Isochronous Speed Control mode, and any other (usually smaller) generators which are connected to the grid are operated in Droop Speed Control mode. If two prime movers operating in Isochronous Speed Control mode are connected to the same electrical grid, they will usually "fight" to control the frequency, and wild oscillations of the grid frequency usually result. Only one machine can have its governor operating in Isochronous Speed Control mode for stable grid frequency control when multiple units are being operated in parallel. (There are Isochronous Load Sharing schemes in use in various places around the world, but they aren't very common.)
On very large electrical grids--commonly referred to as "infinite" electrical grids--there is no single machine operating in Isochronous Speed Control Mode which is capable of controlling the grid frequency; all the prime movers are being operated in Droop Speed Control mode. But there are so many of them and the electrical grid is so large that no single unit can cause the grid frequency to increase or decrease by more than a few hundredths of a percent as it is loaded or unloaded.
Very large electrical grids require system operators to quickly respond to changes in load in order to control grid frequency properly since there is no Isochronous machine doing so. Usually, when things are operating normally, changes in load can be anticipated and additional generation can be added or subtracted in order to maintain tight frequency control.
One method many electrical grid operators use to control grid frequency is called AGC, or Automatic Grid Control. Units being operated in AGC get their Droop Speed Control speed setpoints adjusted remotely in response to commands from the system operator(s) to maintain grid frequency.
There really is a dearth of material on Droop and Isochronous governor control, and much of what is written is very difficult to understand and, frankly, is explained in unrealistic terms. One of the best authors on the subject is Charles I. Hubert; his 'Preventive Maintenance of Electrical Equipment' and 'Electric Machines: Theory, Operation, Applications, Adjustment, and Control' both contain some good sections (though brief) on the two speed governor control modes.
This author is hopeful that someday soon, an article on Wikipedia will be started and that the collective thoughts and efforts of many knowledgeable people will be combined into one thoughtful and insightful-and most importantly, understandable--definition of the concept of governor speed control modes.
markvguy
We have a situation with 2 x 15MW generators and a 14MW load. We want one to take the maximum load (becasue it is running on cheap gas) and the other to run on diesel, which is expensive. It is suggested that we can do this my running one on droop and one on isoch. We have a PMS system. Any ideas how to do it ???
If one trips out we want the other one to be able to accept the load
If one trips out we want the other one to be able to accept the load
The term "PMS system" is not familiar; can you explain the acronym and describe what you are talking about, please? Please try to remember that to many people the acronyms bandied about a plant on a daily basis may not be familiar to others so when posting a question with an acronym it's always a good idea to explain the acronym.
Presuming you have a small AC (Alternating Current) electrical grid/load that is supplied by one or both of the two 15 MW generators and is NOT connected to any other source of electrical energy or electrical grid, it would be hard to understand how the frequency is controlled and maintained if one of the units is not run continuously in Isochronous mode. Is there some special kind of frequency control which is acting through Droop speed control to maintain the frequency on the grid? Do the operators control the frequency manually? Does the load not vary much, so that Droop speed control can be used to maintain grid frequency?
When a generator is being operated in Isochronous mode and another generator whose prime mover is being operated in Droop speed control mode is paralleld with the Isochronous machine, the load on the Isochronous machine is a function of how much load the Droop machine has taken/accepted from the Isoch machine.
For example, if the load is 14 MW and only one unit is supplying the load, its governor is usually being operated in Isoch mode to maintain grid frequency. If another unit is paralled to the load with the Isoch machine it is usually done so with the second machine's governor in Droop mode.
As the Droop machine is "loaded" the tendency would be for the grid frequency to decrease--but the Isoch machine reduces its power output (and generator output) to maintain the frequency. (Remember: The electrical "load" on a grid is NOT a function of the number, rating, or output of the generators connected to the grid--it's the combined total of the "consumption", the motors, lights, transformers, etc., which are connected to the grid.) So, if the Droop machine in this example was loaded to 7 MW, the Isoch machine's load would automatically drop to 7 MW. If the Droop machine was loaded to 12 MW, the Isoch machine's load would automatically drop to 2 MW.
One cannot "load" an Isoch machine by pushing or holding the RAISE SPD/LOAD button or handle--if one does so, what he/she will be doing will be increasing the frequency setpoint and in doing so the grid frequency will increase.
The load on an Isoch unit is "controlled" by the amount of load on the Droop machine, in this simple example of two generators one of which is being operated in Isoch mode and the other in Droop mode.
Now, there are Isochronous Load Sharing Schemes (is that what's in operation at your site?) whereby multiple units can "share" the task of maintaing grid frequency--but these are not very common and require tuning and testing, both of which make many people very nervous. And, as the size and nature of loads tend to change, the schemes need to be re-evaluated and re-tuned and re-tested to ensure they are working as required--another expense and effort many companies aren't willing to expend once a plant has been commissioned and put in service....
Can either machine be automatically switched to Isoch mode (by, say, a breaker status contact)?
It's up to you to decide how you want to operate your machines: Load the unit running on cheap gas fuel to 13 MW by running it in Droop mode and the load on the other unit which is running on distillate fuel (which should be operating in Isoch mode) will drop to 1 MW. If the Droop unit trips, the Isoch unit will very quickly increase its output to maintain the load AND the grid frequency.
OR, put the unit running on distillate fuel in Droop mode and operate the other unit running on cheap gas in Isoch mode and only load the Droop unit to 1 MW. However, in this scenario, if the Isoch unit trips, the Droop machine will maintain the load BUT the grid frequency will drop until the operator either raises the unit's Droop speed control reference OR puts the unit's governor is Isoch mode.
The choice is yours. But we'd still like to know what a "PMS system" is, and how the units are currently being operated....
markvguy
Presuming you have a small AC (Alternating Current) electrical grid/load that is supplied by one or both of the two 15 MW generators and is NOT connected to any other source of electrical energy or electrical grid, it would be hard to understand how the frequency is controlled and maintained if one of the units is not run continuously in Isochronous mode. Is there some special kind of frequency control which is acting through Droop speed control to maintain the frequency on the grid? Do the operators control the frequency manually? Does the load not vary much, so that Droop speed control can be used to maintain grid frequency?
When a generator is being operated in Isochronous mode and another generator whose prime mover is being operated in Droop speed control mode is paralleld with the Isochronous machine, the load on the Isochronous machine is a function of how much load the Droop machine has taken/accepted from the Isoch machine.
For example, if the load is 14 MW and only one unit is supplying the load, its governor is usually being operated in Isoch mode to maintain grid frequency. If another unit is paralled to the load with the Isoch machine it is usually done so with the second machine's governor in Droop mode.
As the Droop machine is "loaded" the tendency would be for the grid frequency to decrease--but the Isoch machine reduces its power output (and generator output) to maintain the frequency. (Remember: The electrical "load" on a grid is NOT a function of the number, rating, or output of the generators connected to the grid--it's the combined total of the "consumption", the motors, lights, transformers, etc., which are connected to the grid.) So, if the Droop machine in this example was loaded to 7 MW, the Isoch machine's load would automatically drop to 7 MW. If the Droop machine was loaded to 12 MW, the Isoch machine's load would automatically drop to 2 MW.
One cannot "load" an Isoch machine by pushing or holding the RAISE SPD/LOAD button or handle--if one does so, what he/she will be doing will be increasing the frequency setpoint and in doing so the grid frequency will increase.
The load on an Isoch unit is "controlled" by the amount of load on the Droop machine, in this simple example of two generators one of which is being operated in Isoch mode and the other in Droop mode.
Now, there are Isochronous Load Sharing Schemes (is that what's in operation at your site?) whereby multiple units can "share" the task of maintaing grid frequency--but these are not very common and require tuning and testing, both of which make many people very nervous. And, as the size and nature of loads tend to change, the schemes need to be re-evaluated and re-tuned and re-tested to ensure they are working as required--another expense and effort many companies aren't willing to expend once a plant has been commissioned and put in service....
Can either machine be automatically switched to Isoch mode (by, say, a breaker status contact)?
It's up to you to decide how you want to operate your machines: Load the unit running on cheap gas fuel to 13 MW by running it in Droop mode and the load on the other unit which is running on distillate fuel (which should be operating in Isoch mode) will drop to 1 MW. If the Droop unit trips, the Isoch unit will very quickly increase its output to maintain the load AND the grid frequency.
OR, put the unit running on distillate fuel in Droop mode and operate the other unit running on cheap gas in Isoch mode and only load the Droop unit to 1 MW. However, in this scenario, if the Isoch unit trips, the Droop machine will maintain the load BUT the grid frequency will drop until the operator either raises the unit's Droop speed control reference OR puts the unit's governor is Isoch mode.
The choice is yours. But we'd still like to know what a "PMS system" is, and how the units are currently being operated....
markvguy
There was a previous reference to "PMS system" (http://www.control.com/1026218262/index_html). From that reference, it can be inferred that the PMS system can be used to control the load of multiple units by supplying load control setpoints (probably in the form of 4-20 mA signals to the External Droop Speed Control inputs) to the prime mover governors.
It doesn't seem that this system could be used to control the load of multiple generators if one of the generators were operated in Isochronous control mode. The Isochronous control mode would probably not recognize the External Load Control signal since it would be applied to the Droop control mode.
It would be most helpful if one uses an acronym in their post that they define the term at least once (the first usage). PMS can be Property Management System, Post-Meiotic Segregation, Permanent Magnet Synchronous, Popular Music School, or, the most commonly found usage on the World Wide Web, Post-Menstrual Stress--but none of these descriptions seem to be applicable to this usage of PMS....
markvguy
It doesn't seem that this system could be used to control the load of multiple generators if one of the generators were operated in Isochronous control mode. The Isochronous control mode would probably not recognize the External Load Control signal since it would be applied to the Droop control mode.
It would be most helpful if one uses an acronym in their post that they define the term at least once (the first usage). PMS can be Property Management System, Post-Meiotic Segregation, Permanent Magnet Synchronous, Popular Music School, or, the most commonly found usage on the World Wide Web, Post-Menstrual Stress--but none of these descriptions seem to be applicable to this usage of PMS....
markvguy
Hello,
In short, a PMS system as we (Marine Industry) use the term is Power Management System (PMS). This system typically control the Diesel (or LNG (Liquid Natural Gas))engines on a higher level (over the govenors) and the system will also control all heavy consumers on the plant (load sharing, load shedding, blackout preventions etc). Also opening/closing of breakers is typically controlled from a PMS system. The PMS system consist of a PLC (Programmable Logic Controller) with I/O (Input/Output) cards and an HMI (Human Machine Interface).
Regards,
Paul
Very nice introduction to Droop/Isoch by the way!
In short, a PMS system as we (Marine Industry) use the term is Power Management System (PMS). This system typically control the Diesel (or LNG (Liquid Natural Gas))engines on a higher level (over the govenors) and the system will also control all heavy consumers on the plant (load sharing, load shedding, blackout preventions etc). Also opening/closing of breakers is typically controlled from a PMS system. The PMS system consist of a PLC (Programmable Logic Controller) with I/O (Input/Output) cards and an HMI (Human Machine Interface).
Regards,
Paul
Very nice introduction to Droop/Isoch by the way!
Thanks for the information!
So, PMS can also mean "Power Management System"... Aren't acronyms wonderful? Especially TLAs (Three-Letter Acronyms)!
It's possible to see how such a system which controls all large consumption, circuit breakers, etc., could be used to provide a Droop speed control reference to a prime mover governor which was "tuned" for desired response (i.e., loading/unloading rates a little faster than typical).
It does seem though, that the PMS system would have to be "disabled" if one of the units were to be run in Isochronous mode. Or at least "de-tuned" to prevent interaction and instability.
markvguy
So, PMS can also mean "Power Management System"... Aren't acronyms wonderful? Especially TLAs (Three-Letter Acronyms)!
It's possible to see how such a system which controls all large consumption, circuit breakers, etc., could be used to provide a Droop speed control reference to a prime mover governor which was "tuned" for desired response (i.e., loading/unloading rates a little faster than typical).
It does seem though, that the PMS system would have to be "disabled" if one of the units were to be run in Isochronous mode. Or at least "de-tuned" to prevent interaction and instability.
markvguy
PMS is the Power mangement system, which is basically a PLC program switcing different modes of generator according to grid breaker or electric network breaker. If grid is not connected, it decides the ISO machine selection through some logic.
Dear markvguy,
A good article and it clears many doubts. Generally people get confused droop mode to load mode and isochronous mode to speed mode. Further to elaborate the droop mode consists of load mode and speed mode.
Regards,
M.Rangacharya
A good article and it clears many doubts. Generally people get confused droop mode to load mode and isochronous mode to speed mode. Further to elaborate the droop mode consists of load mode and speed mode.
Regards,
M.Rangacharya
Almost forgotten--this website:
http://canteach.candu.org
has excellent technical information on electrical power plant fundamentals.
This page/pdf file in particular has good information about Isoch and Droop Governor Control!
http://canteach.candu.org/library/20030801.pdf
And, they're costless (i.e., gratis, free)!
markvguy
http://canteach.candu.org
has excellent technical information on electrical power plant fundamentals.
This page/pdf file in particular has good information about Isoch and Droop Governor Control!
http://canteach.candu.org/library/20030801.pdf
And, they're costless (i.e., gratis, free)!
markvguy
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