Power Station Grid Synchronization

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

There are too many misleading texbooks on the subject to even bother listing. Since if you noticed the blackouts in the northeast US over the last 60 years, the "grid" is a complete fiction, invented by your state power regulators, not a national organization of anything. So the only way to synchrinize any two pieces of wire is basically what amounts a high power phase-locked loop.

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.

D>> Hi,

Interesting. I never knew that. I found these. (They get a little repetitive).

a typical day what is the (peak) combined MW being transmitted over these dc links? A tiny percentage of all the power being consumed?

--------- Unfortunately, in phase locking a generator to a system which consists of a "grid" (which is not a fiction) the result is that the output of the generator will be 0.

Do not try to apply electronic ideas to a power grid which involves both mechanical and electrical . They very often , at best, don't work. Also considering the number of independent variables and non-linearities involved, electronic systems, including computers, are relatively trivial and uncomplicated.

Phase locking is the ideal in smoothly synchronising a generator to the grid BUT once the machine is "on line" it is neither beneficial nor wanted. Shifting the phase of a generator with regard to the other generators on the system is necessary for production of power from that generator. Of course the dynamics of the electrical system and the mechanical systems involved are factors.

Another case is maximum power transfer: Maximum power transfer is not a desirable operating strategy from an efficiency viewpoint or from a stability viewpoint. Not only will it not be efficient, it would not be a possible operating regime.

So sayeth someone that has probably never brought a generator on-line.

The 'grid' is what it is. A major network of interconnected generation and load stations. There are actually several 'sections' that are *not* synchronized, such as the west to east and Texas has it's own 'grid'. Nevertheless, there are interconnecting points with DC links to allow power to flow between sections.

A major part of the reason for the blackout in 2003 was 'grid' disturbances in Ohio, lower Michigan, and Ontario affected power flow over a much wider area, up through New York and into New England.

As for your ideas about 'phase-locked loop', well, let's just say you haven't taken any power transmission courses or operated any transmission lines, have you?

daestrom

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

repetitive).

In a typical day what is the (peak) combined MW being transmitted over

100% correct. "There is no grid"!! A huh. What is it I parallel my gas turbines to everyday? My hot-tub?

David

It is 100% pure fiction, since the only thing morons with 1000 MW generators are coupled to is four foot roller bearings and Enron retards than can mumble "grid" in four New Dork languages.

--------------

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.

---------- 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.

What is there to learn ?

Graham

On Feb 14, 7:56 pm, snipped-for-privacy@netscape.net wrote: >

So...when *you* plug your toaster into the wall socket, you are drawing power from what exactly????

David

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

------------------ There are many good technical and economic reasons for a "grid" interconnection. You mention blackouts but consider this- the overall reliability of the grid is well above that of any electronic system in existence and the interconnections aid this. That doesn't mean that MBA's in charge of some utilities know any more than you do about this and practice short term, short sighted policies. Their ignorance is just as great as yours. That is the problem.

--------- 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. -

Of course there are, But the economic problem with power grids, is that they all only concern GE and Westinghouse and no other corporations,

From Corning.

Since GE is too stupid to make toasters that work in anything other than moron Boeing 10g fields, And Black&Decker is too pathetic to make anything other than 7-11 pinups for Ford morons.