Electronics > Power/Renewable Energy/EV's

Question on how grid stays in phase across long distances

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AConfusedGabriel:
I've been working with high speed signals for a few years now and one thing that always confused me is how the grid operates over such long distances while staying in phase. The western interconnection spans around 4,000km. If information travels at the speed of light, that would be around a 13.3ms delay. 60Hz only has a period of 16.66ms! If all plants try to stay in-phase, how do power plants interact with other plants further away?

IanB:
Plants don't try to stay in phase. They are compelled to be in phase with the local grid and have no possibility of not being in phase without things blowing up.

Every plant is in phase with the local part of the grid it is connected to, and every part of the grid is in phase with the nearby regions on the same grid. Since every part of the grid is in phase with nearby regions, which are in phase with their nearby regions, and so on, then it follows that the whole grid is in phase with itself, and in turn with all connected plants.

This is not to say there are not small variations over time and distance, which of course there are, but the small variations are much less than the overall state of the whole.

Psi:
If you could magically look at the whole grid you would see that it's not in phase between points that are very far apart.
However this does not actually matter precisely because the points are that far apart.

The grid as a whole is not kept in phase, it is kept in sync.
Phase only matters when you are talking about two points that are close enough to compare against each other.

brucehoult:
Also, synchronous generators are also motors. They stay in synch with the local area phase no matter whether they are adding energy to the grid or extracting it, because they stabilise to some small but finite +ve or -ve phase difference depending on whether they are adding or extracting energy, and how much.

Also see "rotating mass", which is what resists the grid frequency dropping when you turn on your electric kettle, until someone or something increases the fuel flow or water flow or whatever. Or I guess now there is "equivalent rotating mass" if you've got one of Elon's Megapacks nearby.

Phil1977:
You can think of waves on the open water.

They are not all in phase, in contrary you can really see the phase by the height of the water and how it moves.

But they are synchronized. The physics of excitation by the wind and inertia of the water create a system where energy (wind) is transferred into the waves (potential and inertia of the water) over a huge area.

The comparison to power grids is of course far off. But the principle is the same: Physics of a rotating generator or modern inverter ensure that power goes into the grid and reactance is avoided. If you can ensure these two properties then you get a stable power transfer without having to care about a "global" phase. The "only" thing you have to control by overall supervision is that the amount of power generated equals the amount of power consumed. ThatÂ´s the main task of grid control.