Question on how grid stays in phase across long distances

[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. That´s the main task of grid control.

[Siwastaja]

Grid does not "stay in phase". It's a tree. Any randomly chosen points of the grids are not in the same phase, if measured against some universal imaginary reference clock.

Power plants do not interact with each other to maintain any kind of phase sync. They just output power in phase with that local point they feed into (which is really simple).

[woodchips]

A lot of discussion on the thread How do Stability of grids with a high percentage of asynchronous sourcing.

If you have a grid going from New York to Chicago and another from Chicago to the other side of New York, then if you want to parallel them then you don't switch the line circuit breakers on from New York to Chicago then from Chicago to New York. With 2000 miles of wire there is a huge time delay as the 60Hz travels from NY to C and then C to NY. You isolate the far end of one NY to C, connect the two NY circuit breakers and then the time delay on both lines at C means that you can just switch the circuit breakers on. If the grid is local, not from NY to C and back, then it all works nicely.

[Andy Chee]

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.

I posted in the other thread a video of Sakuma HVDC station, Japan.  This station requires a DC reactor.

[RoGeorge]

If all plants try to stay in-phase, how do power plants interact with other plants further away?

All the generators in the same power grid are in sync (which is not the same as being in phase).  Only nearby generators are in phase.  For example, when a new generator is connected to the grid, first the new generator is brought in sync with the rest of the grid, and connected when there is no phase difference between them.

Apart from that, power plants do not just connect/disconnect generators at their will, there is a National Dispatcher bureau in charge with operating the national grid (at least here, in Ro).  The dispatcher tells when to connect or disconnect generators, when to re-route the power across major HV lines, etc.

The power plants do not interact much with each, they obey the national dispatcher.  There is some communications along the nearby power lines, but that is mostly for automated protections.  Power plants do not negotiate with each other regarding the levels of power they deliver (which affects the phase).

The discipline when maneuvering the national power grid reminds of military discipline, or of the discipline of a control tower from aviation.  This is because a faulty maneuver may damage equipment that cost millions, or even worst, may leave a huge area (if not an entire country) without electricity, and for such an outcome the damage/consequences are incalculable.

All the maneuvers are described to the finest detail, all steps are followed to the book, all possible outcomes (and how to react to that) is known by heart.  During a maneuver, each step is executed with confirmation coming from both the human operators and the machines/instruments.  Often there are people in the field to look at the equipment, and to visually confirm each step was indeed executed successfully.

The discipline and professionalism of the people involved with the national power grid is hard to imagine without witnessing them at work.

[brucehoult]

The discipline and professionalism of the people involved with the national power grid is hard to imagine without witnessing them at work.

... until some idiot maintenance contractor undoes all the bolts on three legs of a 220 kV pylon located at a change in direction of the lines.

https://www.rnz.co.nz/news/national/520189/speculation-on-reason-behind-pylon-collapse-unhelpful-transpower-says

[Andy Chee]

Or how about a generator being back-fed by the grid, becoming a motor, and then exploding from overspeed/overheating:

[Seekonk]

I saw a video where the police in England filtered the power line hum in the audio and could match up the exact time and general location of where the video was taken. All this from the frequency signature that the utilities just happen to store.

[langwadt]

I saw a video where the police in England filtered the power line hum in the audio and could match up the exact time and general location of where the video was taken. All this from the frequency signature that the utilities just happen to store.

I believe it is also used to see if a recording has been edited, by detecting gaps and jumps the hum phases

[IanB]

I think time stamp mainly, not so much location: