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Why Does the U.S. Have Three Electrical Grids?

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Re: Why Does the U.S. Have Three Electrical Grids?

#121

Post by eythian »

tinix wrote: post #85
jdswain wrote: post #68

Earlier quoted context omitted.

Wouldn't a better solution be to make them all in phase with each other? Then there wouldn't need to be any HVDC interconnect.

Consider the distance, and speed of light, and the speed of electricity (1/100th of that). I don't think it's truly feasible to keep that much physical space in sync. Hmm...

The speed of electricity isn't 1/100th the speed of light. IIRC it's something closer to 70% in copper. The speed electrons move is much lower, however something more like cm or m per second (presumably depends on voltage.) However, this isn't related to the speed of electricity which is analogous to how the speed of water through an (already full) hose isn't related to how soon water starts coming out the end when the tap is turned on.

I've also heard, but I can't explain so you'll have to look it up yourself, that none of this matters when keeping a grid in sync anyway. It just works out.

Re: Why Does the U.S. Have Three Electrical Grids?

#123

Post by hahajk »

kd5bjo wrote: post #120

IIRC, one of the reasons Texas has a separate grid is to avoid Federal regulation: The source of the US’s power to regulate electricity is the interstate commerce clause in the Constitution, which doesn’t apply if nothing crosses state borders.

I also heard that having its own power grid makes it an appealing place to build data centers. Especially for the military who are worried about power-grid-hacking.

Re: Why Does the U.S. Have Three Electrical Grids?

#124

Post by MrBuddyCasino »

Too much efficiency is dangerous: it makes the overall system more vulnerable because it removes redundancies, increasing systemic risk. Decision processes are not scale-invariant: politics, and therefore susceptibility to corruption, increases, transparency decreases.

Not saying a unified grid is not worth it, but there are downsides that might not be immediately obvious.

Re: Why Does the U.S. Have Three Electrical Grids?

#125

Post by tlamponi »

danw1979 wrote: post #101
nickff wrote: post #3

The most interesting national electricity grid has to be Japan's, with two completely different networks operating at different frequencies, and connected by HVDC. https://en.wikipedia.org/wiki/Electricity_sector_in_Japan

"The total transmission capacity between the two grids is 1.2 GW" That's a tiny amount for an industrialised nation of 125 million people, considering that the border between the grids cuts right between Tokyo and the other western centres of population. I think this, and the nuclear power shutdown, lend some context to Japan’s push for a hydrogen economy.

That's only the inter-grid exchange capability, over AC1 DC AC2 transformation, not the total one

If you read the article, the US has about the same inter-grid exchange capability for the west and east coast grids.

Japan has alone over 50 GW of solarpower, and that's only a small share of their energy mix.

They produced 1009 TWh in 2015, that'd be an average of 117.95 GW, and usage is seldom average, but with daily peaks. I'd take an educated guess and say their nets can handle multiple hundreds of GW to up to a TW just fine..

Re: Why Does the U.S. Have Three Electrical Grids?

#126

Post by MisterTea »

fomine3 wrote: post #18
nickff wrote: post #3

The most interesting national electricity grid has to be Japan's, with two completely different networks operating at different frequencies, and connected by HVDC. https://en.wikipedia.org/wiki/Electricity_sector_in_Japan

That's still pain. When I (live in 50Hz area) buy cheap dehumidifier, I get lower performance due to lower frequency.

AC motor speed is frequency dependent so your dehumidifier compressor and fan motors are running slower and producing less mechanical power.

Re: Why Does the U.S. Have Three Electrical Grids?

#127

Post by Shivetya »

Pfhreak wrote: post #4

> Everything within those separate zones is synched up. So you’ve got your 60 hertz AC wave; 60 times a second the AC power flow is changing direction. And all of the generators, all of the power consumption within each zone is doing that synchronously. But the east is doing it on its own. The West is on a different phase. Same for Texas. Folks may not realize that power is transmitted in three phases in the US. AC p…

I always love this one explanation of why three phase and not some other number of phases, like six or twelve[0]

Starting there is of course an infinite rabbit hole just on youtube to understanding power generation anywhere in the world and how it changed through history

[0] https://youtu.be/HqZtptHnC2I

Re: Why Does the U.S. Have Three Electrical Grids?

#128

Post by MisterTea »

mauvehaus wrote: post #32
nickff wrote: post #6

Earlier quoted context omitted.

>"[W]e basically always have at least one phase providing power at any time." This isn't really how three-phase power works. In household settings, you're usually getting only one phase, so all your power comes from that phase. Different neighborhoods get different phases, so they're roughly balanced loads. Industrial (and some consumer) users get two (208V) or three phases (480V), and they get power from the differe…

Typical residential service in the US is 240v single phase. The transformer on the pole is putting out 240v, but there's a center tap on the transformer that's bonded to ground. That's your neutral. The other two legs are essentially +120v and -120v relative to ground/neutral. Your dryer hooks up to both legs and sees the full 240v. Don't ask me how grounding works for 240v appliances. I have no idea. I am not an ele…

> As far as I understand it (not very) there is no such thing as two-phase power.

Because it's obsolete (but still exists in some places like center city PA). Two phase has two windings in the generator 90 degrees apart. Service was delivered via 3, 4, or 5 wires. Three phase beat it for a number of technical and economical reasons.

Re: Why Does the U.S. Have Three Electrical Grids?

#129

Post by MisterTea »

nickff wrote: post #36
mauvehaus wrote: post #32

Earlier quoted context omitted.

Typical residential service in the US is 240v single phase. The transformer on the pole is putting out 240v, but there's a center tap on the transformer that's bonded to ground. That's your neutral. The other two legs are essentially +120v and -120v relative to ground/neutral. Your dryer hooks up to both legs and sees the full 240v. Don't ask me how grounding works for 240v appliances. I have no idea. I am not an ele…

The 240V that you're talking about is what I mentioned as 'mirroring'. There definitely is such a thing as two-phase power, my electric car charger is 208V from two industrial phases, and our reflow oven is 208V, from two similar phases.

That's still single phase as the power you're seeing is the vector sum of the two phases.

Re: Why Does the U.S. Have Three Electrical Grids?

#130

Post by MisterTea »

nickff wrote: post #6
Pfhreak wrote: post #4

> Everything within those separate zones is synched up. So you’ve got your 60 hertz AC wave; 60 times a second the AC power flow is changing direction. And all of the generators, all of the power consumption within each zone is doing that synchronously. But the east is doing it on its own. The West is on a different phase. Same for Texas. Folks may not realize that power is transmitted in three phases in the US. AC p…

>"[W]e basically always have at least one phase providing power at any time." This isn't really how three-phase power works. In household settings, you're usually getting only one phase, so all your power comes from that phase. Different neighborhoods get different phases, so they're roughly balanced loads. Industrial (and some consumer) users get two (208V) or three phases (480V), and they get power from the differe…

ConEd standard* service in NYC provides 120/208 three or four wire service from a wye connected transformer bank. With the density of the city it's easier to just run three phase all over and let homes pull alternatingly off the hots. So homes connect A-B, B-C, A-C and so on.

Three wire service means you get two hots and a neutral and is considered a single phase "open wye" service. BUT you can reconstruct the third phase from the two half vectors in each phase using transformers.

Four wire gives you full three phase service so you can run big motors, machinery, lots of lighting and such.

*Though plenty of neighborhoods are fed 120/240 or mixed. I'm on 120/240 yet the next block is 120/208. Sucks because I want my three phase.

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