Smart Grid

Dear Tornado

Thanks... In a power line, there is 2 sources so power can flow in full duplex mode or half duplex mode?

Thanks ya I accept duplex cant be used here. Can you say Is it possible to control power flow from a source independent of load/

There is a generator 100kVA and solar power home capacity 10kVA(5 kVA own use+5kVA for exporting to Grid) which also connected to grid load increased to 120 kVA in this situation how we can avoid home from overloading and we can overload the generator to compensate extra 15 kVA power

You cannot control power independently of load.

You "might" be able to control voltage, or possibly even amperage, but you often do that by adjusting the load, so whats the point?

Here are some formulas.

However, that being said, I suspect the real answer to your question lies in Thevenin's Theorem, and its applications. If you don't know how to thevenize your circuit, then why the heck are you playing with such complex circuitry?

you have a 100kva generator and 10kva PV panel both connected to the grid, with a load of 120kva, right?

in this case your deficit is only 10kva, none will be overloaded, the deficit will be compensated from the grid, if your control system is "smart" enough

rhkramer,

I would vote your post as good answer, but there s a small error to rectify before,

the power flow is related to frequency difference not to the voltage, the voltage difference will cause a flow of reactive power only

regards

Maybe the OP is asking if his system returns power back to the grid, will the electric meter run backwards?

Good point, thanks!

Hi,

Since reactive Power is a condition dictated by the load (unless a synchronous machine is used as a motor, over-excited to produce capacitive power to compensate...), If the voltage output is manipulated, don't you think that the result is actually increase or decrease of the active power being shared? In this case, of course, the reactive power share is de facto also shared (or shifted to the other gensets on the grid).

The frequency is supposed to be fixed in a parallelling system. The fact that you try to increase the speed of the genset, will only mean that you are taking more of the load, which is translated by the AVR to an increase of the voltage to force more current to the grid. The increase of field current creates a load on the shaft and therefore keeps the actual speed the same.(hence the frequency stays the same). If the speed is increased dramatically, the magnetic coupling of the genset to the grid will be compromised and the set will be out of synch ... consequences???

Le Noble (Post #6)

This is incorrect! The frequencies have to be the same. Only the voltage and phase can be used to control the power flow (real and reactive).

While the grids are intrinsically bi-directional, the protections are not. This is one area where the work has to be done. Some (if not most) transformer protections do not accept reverse power.

your quote :Only the voltage and phase can be used to control the power flow (real and reactive).

euhh!!!!

please tell me how,with the phase, you control real power flow in this case (100 kva generator connected to an infinite grid )

With due respect..

Voltage-reactive

RPM-real

this is the good combination

while in synchronism, there is no phase difference, both systems are in phase (this is the meaning of word synchronised, as per my poor understanding of english)

you control the real power flow and amount to an element on the grid by the RPM of its prime mover, with reference to the grid frequency

I used the word frequency ( wich is usually directly linked to RPM) to respect the technical background of the OP, and not to confuse him while talking about RPM of a PV system, but unfortunatly this confused our Canadian friend Marot.

Sorry for this,

I hope my idea is clear

Regards

Actually, I am not confused, this is my line of work. (Note that in my post, I didn't say what controls what. I only said that the voltage and phase are your only variables for controlling the power real or reactive).

Your understanding of the control is an over-simplification of what is really happening.

Once you close the breaker and connect the generator on the network, you loose control of the synchronous generator RPM as it becomes fix until you over do it and get a pole slip. Asynchronous generators work differently.

Under lock (synchronized), your RPM governor becomes a power control. When you change the power setpoint, you change the phase between the generator and the network. In theory, you could change it by +/- 90 degrees. In practice it is much less. The phase shift affects mostly the real power but the reactive power is also changed. When you change the voltage, the reactive power is changed and the real power change as well in a smaller amount.

The reason for this is that the power flow depends on the vectorial combination of the generator phase and voltage. They are linked together by trigonometric relationship with the impedance. In most systems, the phase angle is small, therefore the voltage has a larger effect on the KVARS than on the KW.

If you are going to design an automatic controller for a generator, you need to take this into consideration together with the complex impedance of the generator and possibly the network impedance.

At your level, you simply plug the sucker in and play with the controls until it sort of work or the protection trip...

your quote:

At your level, you simply plug the sucker in and play with the controls until it sort of work or the protection trip...

What do you know about my level? I simply replied within the technical level of the OP, who is not interested neither in your level nor mine,

Cheers

BlaBlablabla...

Again dont talk about levels , while you know nothing about mine.

I am not here for a fencing to show levels, I am replying the OP in a simple language could be understood by all levels.

To an end user what is easier to understand the theory of rotating fields, like MMF vector amplitude E = KNΦf = KNΦpnS = K' ΦnS, and the direction of rotating field when the stator field is locked to the synchronism frequency of stator, or just with simple words anyone can understand,

increase the field excitation current (which increase the generator voltage) to increase your part of KVAR,

and increase / decrease the RPM of your prime mover (wich increase / decrease the phase difference between two vectors)to increase/decrease the part of real power..

BTW, I referred to a post by you about similar thread

http://cr4.globalspec.com/thread/67687#comment715508

I didnt see any mention for the phase, rotating vectors,who is ahead who is behind....you talked about just speed voltage,

is it question of level?

cheers

Actually, I think changing the excitation (voltage control) will cause reactive current to flow between the generators. Increasing the engine throttle on one will increase the amount of real power (kilawatts) delivered to the load and decrease the kilawatts from the other generator. The more the throttle is increased, the more the rotor field leads the stator field. On the other hand, if the throttle is reduced enough, the rotor field will lag the stator field and the generator will act as a motor and absorb power from the bus.

This is an overall reply.

Generators on the same net HAVE TO BE on the same frequency, or better shut down before destroyed by excessive current. Setting that abnormal case aside, in an well regulated net just 5 cases should arise among generators:

1,. Same phase, same voltage. The load is shared based on the output impedance of the individual, paralelled generators.

2,. When there is a deviation from 1,. If the output voltage tries to be higher on one, it shares a higher portion of the load.

3,. When the voltage tries to be lower, the portion of the load is lower. If it is low enough, the generator acts as a motor instead.

4,. When the voltage phase of one is ahead of the other, it adds an inductive component to the real power.

5,. When the voltage phase is retarded, it adds a capacitive component.

Power companies charge extra to large customers for 4,. and 5,. having to perform phase correction duties on the top of delivering real power. For them, these circulating currents are a nuisance to be eliminated.

To the basic idea "Smart Grid".

Let me explain in my best Shakesperian English: There ain't no smart grid (outside the internal power companies interconnects), and there won't be neither:

There are already enough industrial Internet attacks (see Stuxnet for example) to show the blooming idiocy of opening it up to any and all hackers.

I interviewed a number of women, what the think of the utility controlling her washer.... etc. Meaning: she want to wash at noon, the utility turns off her washer, allowing it only at midnight. Answer: over your dead body!!! When she needs it, she wants it. Period.

You are free to disbelieve. So, go home, and ask your better half, and report back. In the meantime, good luck!! Forcing the needs of the significant half of the population? Riled up they will vote away your funding in no time flat.

Thanks leveles Now I am answering for your view about smart grid not technical content

Smart Grid is not only control your washer it integrates Solar panel or wind mill in your house to Grid system. So you can export power when you have excess power. Also, developing countries like India we are facing several hours blackout due to faults which is also can be reduced. So people those who wants green can participate in Smart Grid others don need.

I did ma UG thesis in Demand Side Load Management when I found 30 HP motor in our college as fully controllable since it is a sewage treatment plant motor.

You are absolutely right in your sentiments, ,and applicable to your circumstances. Me having arguments with solutions for your problems? No. And I do not care what you install. Whatever fits you is ok.

BUT, smart grid obviously means different things for you and me. I was responding to the standards proposed. They contain unhealthy ideas any large energy producer have to be concerned about. And, I repeat, the standards proposed were designed WITHOUT the input of our women (by the last account 50% of the voting population, and mostly running the household). So, buddy, are you sure, you really want to make pronouncements without them??

Mr.Dave is correct.

I understood him Thanks for his good explanation.

I have doubt that to export power from home to grid. Our home power source should synchronise with grid. So how is itp ossible. Since, I went to power station for Internship where it took 2 days for synchronising 500 MW generator to grid.

Try "Perfect Power" by Bob Galvin and Kurt Yeager. In partiucular the book addresses the issue of bi-directional power via the application of microgrids. Bob is the former chairman/CEO of Motorola and Kurt Yeager was the CEO of the Electrical Power Research Institute (EPRI) for many years until he retired recently. It a great "insiders" look at the issues and opportunities involved with the National Grid, Smart or otherwise.

Thanks a lot...

But in India it is not available. I called to book shops. they said they don have. Can you please send the publisher of this book or e-book link.

Google and Amazon to the rescue...

http://www.amazon.com/PERFECT-POWER-Microgrid-Revolution-Abundant/dp/0071548823

Dave I understood Thanks for ur good explanation.

I have doubt that to export power from home to grid. Our home power source should synchronise with grid. So how is itp ossible. Since, I went to power station for Internship where it took 2 days for synchronising 500 MW generator to grid.

Synchronization is done by an inverter that electronically synchronizes. The lock-in can be done nearly instantaneously to a few minutes depending on the control system used. I am involved in smart grid energy storage.

Dave

Try searching the internet. I work at a much higher level but there are many simple slide presentations on the net about smart grid.

Thanks as u said I referred many websites today but I cant find website which are very good at technically related to Smart Grid

Could u suggest any websites

Regards,

Mansoor

What type of "technically related" info do you need? Here's a sample of useful sites from Google University...

http://www.oe.energy.gov/smartgrid.htm

http://www.smartgridnews.com/

http://en.wikipedia.org/wiki/Smart_grid

Try getting the book referenced in Post #19 o f this thread.