# Power Station Grid Synchronization

Hi,
I am trying to learn more about synchronizing a mini power station to a national grid network. Can someone recommend a good book that
explains this. And what are the equipments used here and who manufacturers these products?
LS
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On Feb 14, 11:58 am, snipped-for-privacy@yahoo.com wrote:

I can explain it simply enough.
The AC power coming from *any* electrical power source is in 3 phases. Each phase is 120 degrees out from each other. They are called "A" "B" and "C" Phases.
In order to "parallel" the 3 phases, each A-B-C phase for your power source (wheather it's 100 watts or 1,000 megawatts, it makes no difference) has to be in "syncronization" with A-B-C phases of the system, which all work in harmony, from Hudson bay to northern Baja California.
In large units, we do this manually (and now, automically) by using what's called a 'synch' scope with a rotating arm (representing the phase angle of the 3 phases as one, in relationship to the phase angles of the sytsem. When they are at "unity", that is the arrow on the meter facing straight up, we close the paralleling breaker. When this happens the system "grabs", quite literaly, our generator and the 3 phase angles move in harmony/synchronization. The 'speed' of the turbine/generator, wheter 1800 RPMs or 3600 RPMs is then forced driven by the system and not your primary energy source (steam). No matter how much more steam (or water as in hydro) you add, the speed with always stay the same. Which is how power is increased because the steam, while not adding speed, adds torque, which, by increasing the DC field, increases megawatts.
In smaller units' such as a DC solar panel collection or small hydro unit, for a home, with say, 3,600 watts (about average usage at peak time around 7pm in most places) this can be done electronically at the inverter. You need the inverter to take the DC and make it AC so the toys in your house can actually use the solar energy...and the inverter is needed to allow exess energy to flow *back into the system* and run yoru meter in a backward direction! The inverters that do this are actually more sophisticated than the automatic volage regulator I'm forced to use at my power plant.
David Walters Control Room Operator Potrero Power Plant, San Francisco, CA
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As for the synchroscope- a set of lights works well. Three sets of 240V lamps (for 120V systems) connected directly across the breaker, phase a to a etc will be all bright when out of phase and all dark when in phase and voltage is close enough -close the breaker. This will not occur when phasing rotation is wrong. . Now consider one lamp connected a-a and the others a-c and a-c and placed in a triangle will give a nice rotating effect- just be sure that the switching is done when the a-a is dark. A major concern is to have the phase rotation correct.
As for the rest of the explanation, there is a technical flaw.
"Which is how power is increased because the steam, while not adding speed, adds torque, which, by increasing the DC field, increases megawatts."
Tain't true.
Increasing the input power shifts the phase of the machine and this increases the power output (and does affect speed but this won't normally be seen if the machine is small with respect to the system) How do you think that you correct frequency? It does NOT increase the DC field (an increase in field -through attempts to raise voltage, will increase reactive output from that machine).
Oh, yes, there are no AC ties from Hudson's Bay to Baja California. Such ties would be unstable. Even between Alberta (tied to the Northwest power pool) and Saskatchewan (tied to the Midwest system) there are no AC links. There are DC, asynchronous links in this case and also a DC backbone link in the NW system which makes it possible to maintain the links from Western Canada through to the Baja.
Don Kelly snipped-for-privacy@shawcross.ca remove the X to answer ----------------------------
wrote:

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Interesting. I never knew that. I found these. (They get a little repetitive).
http://en.wikipedia.org/wiki/Image:Nercmap.JPG
http://en.wikipedia.org/wiki/Western_Interconnection http://en.wikipedia.org/wiki/Eastern_Interconnection http://en.wikipedia.org/wiki/Qu%C3%A9bec_Interconnection http://en.wikipedia.org/wiki/Texas_Interconnection http://en.wikipedia.org/wiki/Alaska_Interconnection In a typical day what is the (peak) combined MW being transmitted over these dc links? A tiny percentage of all the power being consumed?
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Not necessarily a tiny part of the total load when you consider lines capable of transferring 3000MW. The energy from Northern Manitoba to the south is all through DC links (see Nelson River and/or Manitoba Hydro ). Much (probably most) of what is exported south from Quebec is through DClinks. The internal link in the NW power pool does have appreciable capacity- it wouldn't actually be worth while if it didn't. As to the actual peak transfer through these lines - I don't know that. There are some links which are small potatoes such as the Alberta-Saskatchewan link which is between two of the regions listed in your first reference. Can these be stronger? Certainly but not with AC links. There are two main reasons for long distance DC transmission. (a) elimination of problems with AC transmission due to long lines provided by an asynchronous tie. (b) Economics.
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Don Kelly snipped-for-privacy@shawcross.ca
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We don't. Frequency is decided by the system once you are paralleled...you can't be out of phase with the system or of a different frequency which is based on speed, not torque. You can increase voltage or lower it via voltage regulation.

You are correct...but total amps through the stator winding are a function of the total generation.

Yeah, true, also between the Western States and Texas/Midwest, I think in Missouri...a DC link flattens the phase angels, then retunes up through inverters. But in effect, one can supply WATTS from Hudson Bay to Baja, *through* the various DC-inter ties. I mention Baja because they are actually part of the California power pool.
David Walters
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wrote:

---------- There is a bit more to it than that. Phase differences exist and must exist. That doesn't mean a frequency difference. If you are in phase with the grid and at the same voltage- you deliver neither power or reactive. If you try to speed up an individual generator, you actually do speed up the system a bit but mainly you advance in phase which leads to more power delivered to the system. The actual frequency is dependent on the governor droop settings and the share of the load taken by a given machine. Another control, (load frequency) system wide is used to control the frequency of the system as a whole by adjusting all the prime movers as desired. This will include changing of load sharing between machines. As to voltage control, an adjustment which can make a big difference in voltage for an isolated machine, will have a much smaller effect on a machine connected to the system because its main effect is to change VAR production from that machine. For example, a generator tied to an "infinite bus" which is a grid which is much larger than the generator- admittedly ideal limiting case- the voltage and frequency is fixed. Any attempt to speed up increases power output. Any attempt to increase voltage results in more Var output. In this limiting case the frequency and voltage do not change. In practice, depending on the relative size of the generator and the strength of its ties to the grid- some voltage and frequency changes do occur.

------ A function of the KVA not KW. --------------------

----- DC links are possible but they don't "flatten the phase angles". In theory one can deliver power from Hudson's Bay to Baja through DC links. However, do these links actually exist or, for those that do, (such as the Alberta-Saskatchewan link) are they significant except on a local basis? I expect that, in the future such ties will be there leading to what may end up as a continent wide interconnection. Certainly the Manitoba south links and the Quebec south links are significant and the internal link in the Northwest power pool is significant as a backbone to that system. In any case, DC links do not control frequency at either end. They inject or suck MW and suck MVARs.
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Don Kelly snipped-for-privacy@shawcross.ca
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Yes, but it starts with the torque developed by more motive force (steam/water) into a turbine. The torque is delivered by the shaft to the generator. You can't shift the phase of the machine without increased torque.
David
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--------- Agreed and I have not said anything to the contrary. I did say power input but as speed is essentially constant, that translates to an increase in torque. There is then a counter torque produced by the electrical system, which is mainly dependent on phase, and a new balance will be reached at nearly the same speed , increased power angle and higher power output The whole system will be at a slightly higher speed - say an increase from 60 to 60.01 Hz and other generation will have lost some load equivalent to the load picked up by the unit being controlled. This will have to be corrected through an external control. If you have a good recording frequency meter you will see the variations up and down that are always occurring as load changes. Certainly the dynamics of the prime mover and the governor are part of the picture. In particular, the governors of all prime movers have droop (speed regulation) and do not try to maintain absolutely constant frequency. This is necessary for proper load sharing between units. -
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Don Kelly snipped-for-privacy@shawcross.ca
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snipped-for-privacy@comcast.net writes:

Since the synchronization will never be perfect, there must still be a substantial surge/mechanical force/BANG at the point the relays close, particularly for the largest generators. Does this cause wear and tear such that components have to be repaired after a certain number of times of bringing the generator online? How large are the largest individual generators, anyway. I know the largest power plants don't put all their power through a single generator.
Speaking of BANG, I heard a description of the first time the St Lawrence Seaway hydropower system (a few thousand MW total) was first brought online, some time around 1960. Supposedly the HV transmission lines themselves went BANG, because the individual wire strands in the cable were attracted to each other when they first carried current. Do HV transmission lines do that (bang) when first placed into service?
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OK. I just imagined that if you had a generator spinning at a rate such that it would generate 60.01 Hz being synched to a 60.00 grid, even if you switched exactly in phase, the grid would demand the thing spin at exactly the right rate and even with a small difference, that's a lot of decelleration or acceleration in a very short time, and with something very massive.

Yes I figured the eggs-in-one-basket would be a major factor.

I wasn't thinking of between phases or bundled conductors, I was thinking of individual wires in a single cable (the big 'wire'). Often such cables have 7 or 19 individual strands, and I believe the ones for transmission lines are aluminum except the center one is steel for strength. Substantial current in parallel conductors (the individual strands) in the same direction attracts the strands magnetically, and supposedly the cables magnetically constricted with a bang as the strands were attracted to each other. I suppose at the voltages involved the strands may be repelled from each other by the charge.
FWIW, the towers in the immediate area are the metal lattice towers with 6 single conductors, none seem to be bundled conductors with spacers. It's a forest of those towers there.
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------------ Your thinking is right and in the scenario the incoming machine would be decelerated and during this time, it would pick up load. At the same time the system would speed up somewhat. If the "droop" or speed regulation of the governor was a typical 5% the load picked up in the above case would be about 0.02% of the machine's rating. How long it would take to decellerate would depend on the intertia of the machine. I doublt whether one, standing by the machine would notice the "bump" Now at 61Hz- you would definitely notice. -----------

------- First of all, the ACSR cables have individual wires in contact with each other. A typical (smallish)conductor may have 26 aluminum conductors over 7 steel conductors and larger conductors will have more layers of each (7 strand is the smallest and not used for HV transmission). Yes there will be some constriction but this will not cause a "bang" as they are already in close contact- some squeeze- true- but the worst squeeze would be under fault conditions. There will be no repulsion due to charges as all these conductors are at the same voltage. ------------

------- These would be 2 -3 phase circuits on the same tower and some would be older lines. Many lines at 240KV or lower are not bundled. At higher voltages, bundling is used for its advantages of lower weight of conductor, lower electric fields in the vicinity of the conductors, lower line inductance and easier installation -hence economic and electrical/mechanical advantages. It is a way to effectively approximate a large diameter single conductor (e.g. 2-0.25 inch radius conductors, spaced 12 inches apart will have an equivalent electrical radius of about 1.7 inches but a fraction(4%) of the weight or cost of an equivalent (solid)single conductor.
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Don Kelly snipped-for-privacy@shawcross.ca
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Don Kelly wrote:

Actually, synchronization is usually performed with the generator frequency (speed) slightly higher than the grid frequency, just to make sure that it comes on line with positive, not negative loading. The load is then immediately raised (generally to about 5%, if I remember correctly). The grid frequency, and consequently the speed of the turbine generator, randomly fluctuates by the sort of magnitude that you are talking about (0.01 Hz) or more (a good deal more in small grids, such as on an island like Taiwan, for example). This is because of the constant step changes in system demand from large loads being switched on and off. The turbine generators are quite capable of changing speed by that much in very short times (fractions of a second); they do it all the time. Standard speeds, by the way, for steam turbine generators at 60 Hz are 3600 rpm for fossil units and 1800 rpm for nuclear units.
Bill Ghrist
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In the REAL World, syncronization is simply not a problem, nor has it ever been one. "Wires getting attracted to each other" is ridiculous, this could only occur if one had opposite graveling voltage, which it doesn't.
Big nuclear plants only have to parallel once every fuel cycle (like every 18months to 2 years) and other plants paralleling the unit's is a piece of cake. this shouldn't even be a discussion as it is not a discussion among power plant operators or grid operators.
Wit the grid, when a large loss of gerneration occurs...like when PG&E was testing a dual-full load trip/paralleling breaker opening with the instant loss of 2400 MWs...that is when you feel it. I was on the day they tested this and it seem that our 210 MW generator almost jumped off it's pedestal! Every generator in the system had to instantly make up for loss of 2400 megawatts which meant the steam governor valves (which respond to "speed of the system" immediately opened up to allow for more power. Fun times...
David

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| Wit the grid, when a large loss of gerneration occurs...like when PG&E | was testing a dual-full load trip/paralleling breaker opening with the | instant loss of 2400 MWs...that is when you feel it. I was on the day | they tested this and it seem that our 210 MW generator almost jumped | off it's pedestal! Every generator in the system had to instantly make | up for loss of 2400 megawatts which meant the steam governor valves | (which respond to "speed of the system" immediately opened up to allow | for more power. Fun times...
I wonder how their generator(s) reacted to that (sudden loss of load).
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| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
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On Feb 21, 2:42 pm, snipped-for-privacy@ipal.net wrote:

I don't know. I suspect because they are DC, at least they were back then, they were able to absorb the lost of generation. BTW...Load is the demand, Generation is they supply. We lost generation, not load, thus voltage was dragged down in the entire system.
David
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wrote:

--------- DC??? Since when since Edison's time has any utility system had DC generators? Particularly ones in the multimegawatt range. DC transmission lines- true but that doesn't change the problem with generators which has a lot to do with the mechanical behaviour of the prime movers.
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Don Kelly snipped-for-privacy@shawcross.ca
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