How Is Grid Phase Managed?

Is this about power factor? If so, then there's yards of information available by entering those words into the Search this Forum box, and clicking on the Go button.

Good question. I have wondered this many times and I don't know the answer. I think that a few months ago there was a show on one of the educational channels that referred to the phasing as being controlled from a "central command center". I suspect that is a true statement but that still does not give the answer.

I suspect that part of the answer might come from understanding that the 60 Hz power frequency is VERY SLOW in comparison to timing that can be obtained from GPS satellites or other sources. Thus, one possible answer would be to issue a directive that a positive zero crossing happened at HH:MM:SS.xxxxx time on xx/xx/xxxx date. From that point forward all zero crossings could be calculated for many years. With accurate clocks you have all the information you need.

There are at least three problems with what I just suggested. First, many years ago I was taught that the power line frequency slowed down and sped up a very small amount based upon load. The power company would balance the speeds out to keep all clocks correct. I don't know for sure that it was true but the sources seemed good.

The second problem with my suggestion is that the phasing would probably need to be adjusted a little based upon what part of the country you are in. Electricity is fast enough that they may not bother with this but every little fraction of a percent of efficiency will start to add up over time.

The third and I'm sure not last problem is that this phase control was done before the GPS satellites were available. Also, it needs to work even if the GPS satellites stop working. Thus, if they use GPS clocks they must also have an alternative method.

In summary, I don't know. Hopefully someone will post the answer.

Ummm...crazy-complicated GPS timing aside, since we already do this...and it's not a future thing...

When a grid is initialized the master control station will start up...all follow on stations will sync to that station's output which is...in essense...the phase controller for the grid.

done.

Maybe it is that simple but with all stations (including the master) going up and down at times it seems like something would go wrong. Having each power station drive the line while at the same time being responsible for phasing to the signal that one of the other stations is driving on the line seems awkward.

I assume little home solar cell systems that sell back power will phase to the incoming line. Big plants that can push around the grid seem like a bigger problem. If I personally were to try to have many large scale power plants all driving the same line without better phase control I suspect I would be the lead story on the evening news.

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Large inverter-based power generators can locally change the power factor. This was one of the concepts discussed by GE in a seminar I went to concerning large photovoltaic plants. e.g. 10 MW.

Each fuel type has advantages and disadvantages,

Of course they can....just like consumers using large inverter power supplies can locally change power factor. That means that the waveform is not necessarily uniform across that grid....which sounds nightmarish, but in actuality, no one has to synchronize with all the various mismatches. Each producer isn't seeing the variations across the gris, they are only seeing the wave form at their own connection.

Does that mean that a cumulative error could actually add up to what would be a destructive out of phase condition which actually does not happen due to the stepping of the phase through multiple entities. Or only a number of degrees of error plus or minus?

I don't understand what you are asking, perhaps you could rephrase. I offer no guarantee that I will be able to provide a decent answer if you do decide to rephrase your question, but the odds are better than they stand at the moment.

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My main contention in that previous comment is simply that everyone interacting with the grid, suppliers and consumers, have an affect on the wave form, but that doesn't create a situation which requires centralized control over all the various connections. I think it is also important to realize that differences in conditions at any moment in time at various locations across the grid, might seem dangerous, but those differences are not seen as any one connection.

Here is a very simple explanation. When a generator is connected to the grid, its rotor (which is connected to some engine) is connected to every other generator rotor on the grid through the magnetic field within the generators and the current in the grid. The magnetic fields act as kind of springs which allow each engine to supply power to the grid according to its own capacity. So once the frequency of the grid is determined by the big players, any other generator on the grid is forced to run in lockstep.

I just came across this. I thought you might be interested....

http://www.ee.co.za/wp-content/uploads/legacy/02%20TT_Variable_Pg34.pdf