Speed of Synchronous Generator

F=(P*N)/120

There might be angular differences between machines, but significant frequency differences? No. Not even 0.1 Hz for any appreciable period of time (more than milliseconds).

As suggested by others, acceleration differences will result in momentary (millisecond) frequency differences, but the poles of the generator rotor will not run at any other speed than the above formula will allow relative to frequency for even 1 second. That would mean that the poles have slipped and that would mean catastrophic damage has occurred.

I have been doing some World Wide Web research on out-of-step relays and their application, and while there can be losses of synchronism between generation areas in a power system or between interconnected systems when detected these events should very quickly result in separation of the affected areas to prevent widespread outages and even damage. In no paper I have read does it ever talk about individual generators being out of synchronism with each other. And even areas of generation which are detected to be out of synch (which is usually much before actual "slipping" of poles occurs) the protection is supposed to operate to isolate the affected areas to protect them against damage.

Many of the manufacturers of out-of-step protective relays have extensive papers on their application and operation.
 
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Namatimangan08

First of all, there is no issue to debate regarding the frequencies of prime movers and resistive loads. At least I'm not the one to debate about it. The issue I was trying to explain is the mechanics between parallel generators. Not generators vs resistive loads.

The physic of t/generators in parallel works as the following. As on of the t/generator tries to move faster it has to drag the rest of system loads to accelerate together due to opposing torque the loads put on the accelerated t/generator. Therefore, the further away it tries to move, the slower its acceleration becomes. So its shaft undergoes retardation. Meanwhile, the frequency for the remaining system will accelerate due to additional opposing torque they put on the t/generator. Naturally, both of them will come into synchronism again if its torque angle does not deviate up to out of step protection activated.

The mechanic to keep the synchronism healthy is not limited by the explanation given by the preceding paragraph. There is another mechanic at work namely the speed droops. Let us take your example to illustrate how this mechanic at work.

Assuming we start from the system under perfect syncronism. All of sudden one t/generator tries to accelerate by 0.1Hz/s (36 deg/s). Assuming the system uses 5% droop set point. Then as the shaft for accelerated t/generated is displaced by 36 deg/s or + 0.1 Hz relative to the remaining grid, its speed droop will reduce the t/generator output by 2%. This provides additional "opposing torque" to reduce its acceleration. By the same time the frequency for the rest of the system has experienced slight acceleration. As a result its shaft cannot move freely to 72 deg as given in your stated example. For the next one second its displacement could be 0.75 times (27 deg)of the first second. By the same time the remaining grid frequency probably has increased by says 10 deg relative to the previous frequency. As a result you can see the total deviation for the next one second is smaller than the first second. For the 3rd one second the droop will keep on reducing the load by says 1.75% more. So the rate of frequency deviation will become even smaller, while the remaining grid frequency is catching up. They will definitely settle down at the same frequency again.

For a stable grid you take for granted relative angle between both of them stays less than 80 deg during steady state load change and during the calculated transient disturbances.

These are the mechanics at work that systematically ensure all the rotating generators cannot go higher than 80 deg faster or slower relative to average system frequency (frequency of the network) assuming the grid is under the normal operating condition.

But then how a turbine/generator or a group of turbine generators can loss its synchronism? Assuming major disturbance that causes one of the turbine generators to undergo acceleration at the rate of 360 deg/s. In this case you can see that natural mechanic cannot stop the deviation to be less than 180 deg since it is completely out of phase already. Even the droop can't help either since its ramp rate is not not infinitely fast. The fastest ramp rate that I know is 15% per second.

Between 90-180 deg it is called transient instability region (Process Value's statement). In this region, system frequency regulation and control may or may not able to pull the frequency back to syncronism again. It depends on whether the shaft displacement has tendency to go above 180 deg or to go below 90 deg region.

Luckily there are many layers protection before it can reach the runaway speed. I will name all that I know. (1) The speed droop (2) Partial shut down generator -hydro (3) Out of step stage 1, 2... (4) Over speed protection Stage 1 (electrical) (5) Over speed protection Stage 2 (mechanical) (6) Breaker failure protection.
 
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Namatimangan08

>Which trip first, breaker or overspeed?

When I first explained my finding to one of the plant technicians he suggested the same question. No. He was not questioning my finding. He denied it by saying that 445 RPM (it was 462 RPM actually due to zero bias error of -17RPM for the speed sensor) was obvious scenario when a t/generator trips off.

We came together to the frequency-load-time plots. The time stem can be set as small as 500ms. We moved the reference line for the plots slowly to the point just before the t/g tripped off. Here are the parameters -the fifth tripping of the day.

Load = 16 MW

RPM = 445 RPM

Trip on over speed protection.

Just after that load, voltage, current etc. became zero.

System frequency was almost flat at 50.00 Hz. Just before the tripping system frequency had increased by less than 0.1-0.2Hz.

During the fourth tripping I had already advised them to reduce the generator voltage for that unit. But nobody took it serious. I was merely a contractor to them. So nothing much I could do to make them listen to me. They repaired here and there then try to put it back on bars. The t/generator tripped off when the operator tried to raise load just after synchronization.

After the fifth tripping I told the plant staff that they had to make sure that they could put the t/generator on bars for my team even that meant they had to stay back for the next 24 hours. They had promised us to put on the t/generator for my team work. Then I told them that, the best chance for them to not to stay back that long was to reduce its terminal voltage from 11.5kV to 11.2kV. For the 6th start, we managed to keep the t/generator until our team completed our work for that day. So all of us went home earlier than 24 hours.

The t/generator tripped again for the same reason a week later.
 
B
The physical law you require is the power transfer over an inductive transmission line. This is given by
(V1 x V2) x sin(a1-a2)/X,
where V1<a1 is the voltage and phase angle at the generator, and V2<a2 is the same at the other end of the line.

So if we use phase angle a2 of V2 as reference, and if V1 is leading V2 by a1, there is a power flow from 1 to 2. If 1 is a generator, this power flow is an output from the system and must be balanced by the mechanical power to the generator:

Mechanical power in = electrical power out + losses + rate of change of shaft kinetic energy.

This balance can be turned into a second-order differential equation relating the rate of change of (rate of change) of angle a1 to the losses (proportional to the rate of change of angle as the relative speed of damping windings) and the power flow down the line.

If mechanical power in increases, the shaft KE increases and there is a very small increase in instantaneous speed of the generator rotor.
This increases the angle of 1 relative to 2 and the electrical power in the transmission line increases to match - the acceleration power falls to zero and the two systems return to synchronism.
If you want more detail, I can send you some references to texts containing the necessary differential and other equations.

Bruce
 
B
A more common scenario is that the incoming generator is rotating slightly faster than the grid - so the synchroscope pointer is rotating clockwise. If it's rotating at 1 rev in 10 seconds, it is doing 0.1 rps faster than the grid - for 60 Hz, the machine speed will be 60.1 Hz.

Also assume that the breaker is closed at 11 oclock - the machine rotor field will be 30 degrees ahead of the field set up by the external voltage.

When the breaker is closed, the rotor position will not change instantaneously because of its inertia. Since the power fed to the transmission line depends on the phase angle (see my other post) there will be a small amount of power fed from the generator - this will acts as a brake on the rotor and pull it into step.

If this was not the case, and the rotor could increase its angle without limit, then at 0.1 Hz relative slip speed the generator angle would increase by 36 degrees in 1 second, 72 in 2 seconds ... But because of the relationship between power and relative angle, the electrical power out of the machine increases and the system reaches equilibrium with the rotor angle stable when electrical and mechanical power are matched.

Bruce
 
So, Bruce Durdle, are you saying that during loading of a machine that it's frequency will increase (say to 50.5 Hz) for a brief period of time (how long, please--just an estimation is all that's required) and that the generator being loaded is actually out of sync with the other generators with which it is being operated in parallel with? And then after some time when the kinetic energy balances out the rotor will return to the same frequency as the other machines?

Do the poles of the generator rotor actually speed up and "jump" ahead? Wouldn't this be slipping a pole by increasing torque and wouldn't it have physical consequences on the coupling and rotors of the generator and/or the prime mover?

I completely understand that there are angular differences under steady-state operation that are a function of load ("torque angle", "load angle", whatever someone wants to call it). And it's also clear that when torque input from the prime mover increases or decreases during normal loading and unloading that there is also an angular change because of acceleration. But that is brief (on the order of milliseconds) and in my experience the poles of the generator rotor stay in synchronism with frequency of the generator stator (the grid frequency).

If the rotor actually sped up or slowed down then currents would be induced on the rotor in addition to the slipping of poles that would be occurring.

I'm sorry to be so dense; I've actually asked this of you in a previous post. I would like to be very clear about this for others reading this post, because my experience just doesn't match with this operating out of synchronism, even for 1 second, or 0.5 seconds.

Again, out-of-step relays are supposed to sense slipping of poles before it occurs to prevent mechanical damage and outages. Some monitor load angles and from what I've been reading they attempt to anticipate an out of synch condition (which would result in slipping of poles) and operate to prevent such an occurrence.

If I'm wrong, then I'm wrong. I have no problem with that. I've been wrong before, and I'll be wrong in the future. Maybe it's just the equipment I work with that doesn't allow me to see these speed differences. But, from everything I was taught and understand an out of synch condition on a generator is catastrophic--in many ways. Loss of excitation relays and out-of-step relays are used to try to prevent this by anticipating such a condition and operating before it occurs.

I've worked on some pretty big machines and they can actually have an effect on grid frequency they are so "stiff" (I think that was the term that was used) and unless some other machine's load is reduced as these big machine's loads are increased the grid frequency will increase (presuming the grid load is stable at the time). And, every generator's frequency (and speed) increases until the machines operating at part load have their droop governors kick in, or an ISO operator reduces load on one or more other generators to bring the frequency back to nominal. But, we're talking about hundredths of a hertz, but not more than a tenth of a hertz. And, it's the whole grid not just one machine.

Thanks!
 
Dear Namatimangan08,

I have been following this post since it started now almost 2 years ago from a simple question, "I have confusion as how increase in electrical load lead to decrease in generator rpm? And why if we increase the generator rpm (by injecting more fuel in gas turbines) increase the power?

At the time this seemed like a simple question, which can get very complex by introducing vector angles, apparent and real power, line impedance etc, etc, etc. But I really appreciate the fact that most people who post here attempt to keep their answers on the simple side if possible.

In my small 10 years of the industry I have not seen even a small amount of what is out there, but I thought and still mostly think I understand the simple idea of how a power system operates. There have been several ways that people who post here have tried to simply explain the idea of how a generator converts mechanical energy to electrical energy, and how these generators work together to provide a stable and consistent flow of power. I still tend to think it is a difficult concept to understand sometimes, and even more difficult to explain, especially for people like me who dislike complex and theoretical math.

But my belief still tends to fall with CSA and Bruce Durdle that once a generator is synchronized to the grid, that its frequency will be the same as any other generator in the system no matter how close or far away. My understanding is that all these generators are rigidly coupled together by the magnetic forces that exist between the stator and rotor of each machine, making multiple generators act like on large single machine. I do understand that a machine might be slightly out of angular phase with the grid at times, when it is being synchronized to the grid, or if an event occurs where a large load is introduced or taken away from an area near a machine. But due to the magnetic coupling inside the generator it is not possible for that machine to operate at a different frequency or speed than the grid it is attached to, unless it losses synchronization by loss of or too little field excitation.

I am really confused by your first post on this thread.

<i>"Straightly speaking two generators in parallel most likely are never have the same frequency. As long as their Synchronism Torque Angle (STA) will not deviate by greater than 180 degree, theoretically their governors can keep them under synchronism."</i>

Can you please explain to me in simple terms what you mean by this statement? I can understand that a generator may have a VERY slight difference in phase angle at times, not normally though and a slight deviation in phase angle is not a difference in frequency. The rotor is still rotating at the same frequency or speed of the grid.

Further you say, <i>“Whatever you want to call it: load, prime mover or generator. All of them are prompt to hunting.” </i> I really don’t understand this statement either. If a generator governor is operating properly then a generator should not “hunt”.

Lastly you state the following, <i>“It is true as pointed by somebody in this forum that a power system doesn't work if there is no frequency deviation. All prime movers (that includes generators) in the system do not recognize what is load. They can only recognize speed. Sound strange right? But it true. So their responses are based on frequency deviation."</i>

FYI- In 2005 our grid system with running capacity of 15,000MW was hunting by the order of +/- 200MW for about 20 minutes. What I'm trying to say is when it comes to load swing (load hunting) system size doesn't matter.”

This seems really scary and foreign to me. I can’t find anywhere that someone says that a power system doesn’t work if there is no frequency deviation. Can you please explain this reasoning to me so I can understand it?

I don’t mean to pick on your posts but they just don’t seem to make sense to how I was taught in school and how I see my plant operate.
 
B
I am saying that, if the mechanical power into a rotor is increased so that there is a surplus of energy in, the result is an instantaneous acceleration of the rotor. This is extremely small and results in a small increase in speed which in turn increases the rotor angle of the generator. This increase in the rotor angle will then act to increase the electrical output of the generator - restoring the original power balance, and reducing the acceleration to zero.

The effect is very short-lived, with the time before equilibrium is restored being dependent on the moment of inertia of the shaft (typically of the order of 1 second). The total change in angle for say a 10 % change in power is about 8 degrees, and if the machine has an inertia constant of 5 seconds (typical for a large hydro or small thermal set), the total KE is 5 x the VA rating. The actual increase in speed as a % of nominal is about 1 %, and I doubt if it could be detected on most machine tachogenerators. We are talking very short-lived infinitesimal effects here.

If you can stand it (bearing in mind earlier comments about differential equations) I can dredge up some hard data from my records and set up a dynamic model for you - but it would be in something like Excel so I'd need an address to send it to.

My comment on synchronising was based on my observations of what works - if the synchroscope is going at about 1 rev in 10 sec clockwise, and you close the breaker at about 11 o'clock, the immediately pick up about 10-20 % forward power with minimum rotor disturbance. I have also seen situations where synchronising was very difficult because the external grid was not strong enough to develop the synchronising torque needed to pull the rotor into lock unless the breaker was closed at top dead center with little or no speed differential - this on plants with a large local load where the incoming link was designed for a small residual power flow.

Bruce.
 
N

Namatimangan08

First of all magnetic coupling between generators and load you can assume they are rigid. It can be treated as rigid coupling for almost all practical purposes. But it was not only me in this thread that proposed two areas might have temporary frequency swing which is called inter areas oscillation. I have seen this swing myself. So I cannot be intimidated by complex vector diagrams that I don't understand if they suggest the other way around. That oscillation can be very damaging but to me it not about load. It is more about generators in parallel.

If the truth about rigidity of that magnetic coupling that troubled you and you want to know the truth, I have posted key words for Google search that enables you to access many articles to support my position regarding this matter. At least one of the articles clear stated it is not rigid at all. It is "elastic". Just go there and read. You don't have to take my words.

> <i>"Straightly speaking two generators in parallel most likely are never have
> the same frequency. As long as their Synchronism Torque Angle (STA) will not
>deviate by greater than 180 degree, theoretically their governors can keep
> them under synchronism."</i>

You run a unit at 3000RPM. Close it breaker to supply load to electrical appliances. A moment later you close another breaker (not synchronization) for a t/generator that is operating 3010RPM. What will happen? Do you think the breaker refused to close just because incoming and outgoing RPM are not equal? No. The breaker will close. If there is no protection against out of phase, the two t/generators will operate at their respective frequencies at least until severe damaged occurred.

If you can measure the sine waves using two oscilloscopes that you specifically filter them out to see 3000RPM and 3010RPM you will see these two sine waves coexist together. If you believe the idea of one frequency then which generator follows which? Why then?

We don't close breakers for parallel generators. We synchronized them. Things get a lot better then. But the fundamental hasn't changed. The fundamental is that two diff frequencies can exist in one transmission line if the sources induce two diff frequencies.
 
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Namatimangan08

I far as I know, out of step relay doesn't do anything rather than alarms plant operators or removes the plant out of the system.

I think you can rely on the droops to keep the synchronism healthy and inertia energy constant to absorb and provide energy momentarily. The amount of inertial energy of a t/generator is one of the parameters that will be clear specified when we wish to purchase a turbine generator.

It is important to ensure the sum of the total inertial energy of rotating mass of the grid supports the stable ramp rate of turbine generators to have a stable system. This is one the reasons why some parts of the world, as you say, constant frequency operation is merely a dream. My country is not spared.

Why is that so? Slowly fundamental for stable grid operations is compromised for lower operating cost. We can view it by looking at the ratio between the biggest per unit capacity of a prime mover and maximum grid (or area) peak demand capacity. As the ratio becomes bigger, the system becomes less infinite. Otherwise, it becomes more infinite. This is one of the indicators to measure how "infinite" is the system that we have.

So if in your country you have this ratio smaller than 2%, I think you can't see most of the issues that I put forward. Ours the ratio is 5%. That ratio is still okay to get a stable grid. But as I told you slowly but surely lower operating cost will dictate the way that our grid is operated.

Too bad, but we have to bear with it.
 
N

Namatimangan08

> I have been doing some World Wide Web research on out-of-step relays and their application,

The paper that I quoted before talks about a generator or a group of generators can go out of sychronism. If you think the paper was written by an academician who has lost touch with reality in his writing, then think about my experienced with a 28MW Pelton turbine generator.
 
N

Namatimangan08

> The physical law you require is the power transfer over an inductive
> transmission line. This is given by
> (V1 x V2) x sin(a1-a2)/X,
> where V1<a1 is the voltage and phase angle at the generator, and V2<a2 is the
> same at the other end of the line.
---- snip ----

Thank you mate. The physic law that I asked specifically was, using your equation (it is a matter of fact I am one of the strong believers in that equation too).

Mechanical power = rate of increase in kinetic of rotating mass + power consumed + losses + power required to change the shaft angular position.

Re written your equation in the form of swing equation for each generator, using torque rather than power, the DE looks like this

Jd^2A/dt + cdA/dt + kA = Induced torque

J= second moment of inertia (kgm2)

A= Angular displacement (rad)

c= Damping constant

k= Stiffness constant

The solutions are of the type of second order DE. Well understood....

There are four possible scenarios about the solutions we may have at the end of our Laplace transform analysis for the second order DE depends upon mainly J and c above. They could end up one of the followings

1. Undamped oscillation
2. Underdamped oscillation
3. Overdamped oscillation
4. Critically damped

http://calculus7.com/id8.html

The questions are:

a) What law of physics that ensure all parallel generators will end up either 1,2,3, and 4 above without exception? Why we can't have a group of t/generators that falls under 2 and the remaining falls under 1, for instance?

b) Assuming there is a specific law of physics that can explain all of them shall end up according to 3 only (as many people believe), then what law of physics that explains they all shall have oscillation with equal amplitude, equal phase and equal time? Remember the swing equations for all turbine generators have little thing to do with electrical network. The parameters used by swing equation as you have agreed all come from t/generator alone.

Thank you.
 
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Namatimangan08

> I have been following this post since it started now almost 2 years ago from a
> simple question, "I have confusion as how increase in electrical load lead to
> decrease in generator rpm? And why if we increase the generator rpm (by injecting
> more fuel in gas turbines) increase the power?

---- snip ----

> Can you please explain to me in simple terms what you mean by this statement?
> I can understand that a generator may have a VERY slight difference in phase
> angle at times, not normally though and a slight deviation in phase angle is not
> a difference in frequency. The rotor is still rotating at the same frequency or
> speed of the grid.

This is my note for this matter. If you want to figure it out how a grid works yourself just don't make simplification until you can be cheated by you own simplification. Put the fact that there are hundreds of t/generators in parallel. Just figure it out how they can maintain their synchronism. At the end of the day you will find it is not as simple as you want to believe.

The age age swing equations that I have shown you is more than 250 hundred years by now, I supposed. Yes. It is a bit difficult to most of us here even to me. Therefore many people wish to take short cut by creating the what so called "rigidly locked into synchronism" to explain how grid work. As I told you, such concept does not exist. Try to goggle it yourself if you can find any scientific evident to prove its existence.

What you can find, i can assure you this, is elastically locked into synchromism. Elastic means they can slip. This is what is termed as generator slip poles. Just goggle it. You don't have to take my words.

The reasons for elastic bonding between generators and loads can occur is due to time taken between torque induced by prime movers and developed torques to match is not infinitely small. It takes sometimes before they match. During this period one tries to move away from the other. But this is not the main issue I like to talk about.

The important point I wish I can share is, if the loads and the generators are not rigidly locked into synchronism then why should we believe all the turbine generators can be rigidly locked into synchronism between them?

Point to ponder.
 
S
> A more common scenario is that the incoming generator is rotating slightly
> faster than the grid - so the synchroscope pointer is rotating
> clockwise. If it's rotating at 1 rev in 10 seconds, it is doing 0.1 rps faster
> than the grid - for 60 Hz, the machine speed will be 60.1 Hz.

You are right but the main reason to keep the speed of the incoming generator to be higher than the grid is to share some load from the grid.
As soon the generator takes the load from the grid the speed will come down according to speed droop setting and it will continue to take the load until it equalise the speed of the grid.

I also agree that the generator frequency may not be exactly equal to the grid frequency, they may be slight changes,but it will be in both side (+or -).

It cannot stay in one way like lagging or leading for long time.
If the generator speed lags behind grid frequency than the generator will give up its small load to adjust to the grid frequency. When its leading it will take some load from the grid to match with grid.
Variations may not be experienced Physically also but always there will be an attempt to match the frequency with the grid. But again it depends on the governor performance too.

This is just my thought.

Thanks
 
Namatimangan08,

You have given us a lot of pause and have made many of reflect on our understandings and experiences.

You are welcome to your understanding and interpretation and you are even free to speak what you believe to be true (freedom of speech is an awesome thing!). Others are also just as free to ask for clarification and/or to challenge what is being said or proposed.

I happened to come upon this thread on a once-per-month visit back to control.com and just wanted to clarify what you were saying. I was not offended by your statement about my misunderstanding; my only interest was to have you clarify your statement. You have done so. I have attempted to add the benefit of my experience and understanding. Others have added their voice to this thread.

As I've said many times before on control.com: I have been wrong before, and I'll be wrong in the future. I try to learn from my wrongs and grow my knowledge in the process. However, this time, I don't think I'm in error.

My hope for forums like this has always been to foster sharing amongst many people, because my personal experience is only one fraction of the experience that's available in the world. I had always hoped that others would begin to post more often and add their experiences. I wanted to just correct "tribal knowledge" myths (completely unrelated to this thread!) and errors, and to challenge people to explain their positions on some issues so as to help them, and others, to be able to reason through issues or principles and arrive at a more thorough and possibly correct understanding.

One of the reasons I have chosen not to post as often to control.com is that I seem to have monopolized most of the Speedtronic-related threads here. Since reducing the number of posts I make some "new" people have come forward with their experience and knowledge (not all of it correct, but none of it false) and that was both encouraging to me, as well as discouraging. It just points to the monopolization I was sensing and reinforces my decision to significantly reduce the number of posts I make to this forum.

However, when I visit the site and see a fairly inaccurate statement about basic principles I feel it necessary to speak up. While my understanding--and explanation--may not be 100% accurate (again, I don't have the knowledge of power system stability theory and practice and experience with transient studies and events) I believe my basic understanding of the operation of AC electrical power systems and synchronous generators is sound. It's disconcerting that I can't seem to find the words to explain it more clearly.

I don't wish to belabour this topic on this thread, or any other thread, any further. We are all free to disagree, and I choose to disagree with your explanation. Others may choose to agree, that's the beauty of freedom.

Best regards, Namatimangan08. Thanks for making us all stop and reflect on our understanding and experience. It's very helpful, humbling and enlightening to do so from time to time.

Back to my once-per-month check-ins now. Keep up the good work, everyone, and don't ever be afraid to post here or to ask for clarification.
 
Dear, Namatimangan08

I have read your replies and will agree and disagree with you on certain points.

I agree that magnetic coupling and rigid coupling are two different things. But my opinion is that ANY coupling can be elastic, it depends on the forces being exerted on it and its relative strength. But again when talking of parallel units they are coupled to the grid they are part of. They can operate at slightly different phase angles but not at different frequencies.

You talk about having a unit operating at 3000 rpm, I assume we are talking about a machine designed for a 50hz system, so I'd rather say you have a machine operating at its designed 50hz frequency. Now you close in another unit operating over frequency, approximately 50.16HZ. So you close the breaker. But assuming the unit has less inertia and power than the grid it is joining, that unit will be pulled or pushed into sychronization with the grid it has just become part of, assuming the unit breaker closes with the phase angles nearly in sync. If the breaker is closed out of sync then large scale damage can occur.

In your other response you talk about generators slipping poles, and you seem to suggest this is normal, which I don't tend to agree with. My understanding was that generators don't generally slip poles. I thought that controls and limits were in place to block this type of event because of the damage it can cause?

I agree that it is interesting to ponder this subject. But to paraphrase the simple question that started this thread was:

1) why does speed of a generator slow down when system electrical load is increased.

2) why does speed of a generator increase when system electrical load is decreased.
It seems like the thread has moved very far away from this topic.
 
B
Managed to troll through my archives and found a reference giving some typical swing curve calculations ("Power System Stability: Synchronous Machines" by E W Kimbark).

As an illustration of the numbers involved, one of his worked examples (related to a fault condition rather than a change in loading) gives a change in power angle from 46.5 to 88.3 deg after 0.35 sec, then reducing to 52.5 deg after 0.65 sec. The rate of change of angle was 0 initially to + 9.6 deg/s after 0.2 sec, (slip speed 0.026 Hz or 0.043 % at 60 Hz). Maximum acceleration in deg/s was 3.5 at 0.05 s.

Not the sort of effect you'd expect to see on a meter!
 
Can you plz make your posts simple and easy so that we can understand easily. I understood that the turbine tripped on overspeed when the breaker was still closed? What is your justification in asking to reduce the terminal voltage to avoid overspeed trip.

Thanks,
Ravi
 
Thanks Mr.CSA for the reply.

Namatimangan08,I have checked the frequencies of our company owned power plant generators which are located at a total distance of 400 km.I checked the frequencies of 5 machines (ours here is 60 hz) and all of them are almost same. the difference being only in 0.02hz which could be due to their meters.You can see the values as given below.

My units-59.962 & 59.961
@ 100 km distance- 59.971
@ 250 km distance- 59.981 & 59.982 Hz.

Regards,
Ravi
 
> one might have higher ramp rate than the other
________________________snip

Namatimangan08, are you sure that changing the machine loading ramp rate causes frequency diff. I have tried loading the machines using manual loading and auto ramp rate but I did not observe this.
 
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