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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?

#21

Post by lutorm »

gerdesj wrote: post #7
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…

"Folks may not realize that power is transmitted in three phases in the US" My office in the UK has three phase power (I own it.) The phase shift thing is to enable putting more power into a place and nothing to do with "so that we basically always have at least one phase providing power at any time." whatever that means. My home only has one phase because I don't need to draw that much power here (yet.)

"so that we basically always have at least one phase providing power at any time" is sort of what makes things like AC motors run better on 3 phases.

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

#23

Post by rbg246 »

ggm wrote: post #2

Australia is comparable in size, split by a giant middle desert (literally and figuratively) And has two grids. Balancing the east coast grid is sometimes hard. Its weak, badly in need of capital investment and somewhat mired in inter-state/federal madness. Personally, I think privatizing the utility function was insane. There are some cool things which emerged after the 1970s grounded capital investment: High Voltag…

https://www.abc.net.au/news/2017-07-18/australian-gold-plate...

It seems to be both overinvested and underinvested? How can it be both? (Sorry looking for insight not trying to disprove what you say)

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

#24

Post by danielheath »

SECProto wrote: post #17
na85 wrote: post #11

Earlier quoted context omitted.

Fire is a natural phenomenon and I don't see how it can credibly be called an invention. That would be like calling water an invention. The others, though, are certainly inventions.

I see a lot more natural electricity (lightning, monthly) than I do natural fire (wildfires? Never)

Almost as though methods to prevent wildfires are one of the earliest human inventions.

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

#25

Post by msisk6 »

samcheng wrote: post #9
aidenn0 wrote: post #5

Earlier quoted context omitted.

The solution is to connect them with HVDC, right? That might not be a great solution for making a single national-grid, but it would allow the 3 grids to mutually borrow from each other, right?

It's a lot of current, so maybe you want superconducting HVDC: https://en.wikipedia.org/wiki/Tres_Amigas_SuperStation

Last I heard the whole Tres Amigas SuperStation deal totally fell apart.

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

#26

Post by nickff »

lutorm wrote: post #16
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…

At least in Sweden, all houses have a 3-phase, 400V supply. This is very different from the US which just supplies one phase to each house even if the supply itself is 3-phase. This is why you commonly see 200+A main breakers on a house in the US whereas in Sweden, 25A is a pretty common main breaker size. (It's as if the US grid characteristics were decided by the copper vendors... ;-)

Well, you have to consider that the USA (and Canada) were on the bleeding edge of technology when they adopted electrical grids. They were left with a... legacy, including the type-A plug and 110V single-phase power to residences.

In your case, I believe each prong of your two-prong plug gets a different phase, so you have 3 possible pairs of phases to power each circuit from. This has the advantage of requiring smaller wires, but the disadvantage of increasing the risk if one is electrocuted.

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

#27

Post by nickff »

crmrc114 wrote: post #14
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…

Close, Three phase systems actually are a carry over from the days of early induction motors. Three phases can easily be connected to create a rotating magnetic field. We don't just use one phase at a time on the grid. All three are active. Phases A and B and C are all 120 degrees out of phase with each other. (That has nothing to do with the 120volts you know of in your house- it just happens to be another 120 numbe…

Three-phase systems are far more than a carry-over from early electric motors. Cars, which have no legacy compatibility issues also use three phases. Three-phase power is a very good balance of simplicity of transformation and rectification with even-ness of loading.

You have to remember that alternators and generators are loading mechanical systems, so it's a bad idea to have huge cyclic variations in the load, which stresses the physical system.

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

#28

Post by [deleted] »

SECProto wrote: post #17
na85 wrote: post #11

Earlier quoted context omitted.

Fire is a natural phenomenon and I don't see how it can credibly be called an invention. That would be like calling water an invention. The others, though, are certainly inventions.

I see a lot more natural electricity (lightning, monthly) than I do natural fire (wildfires? Never)

[deleted]

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

#29

Post by siddboots »

ggm wrote: post #2

Australia is comparable in size, split by a giant middle desert (literally and figuratively) And has two grids. Balancing the east coast grid is sometimes hard. Its weak, badly in need of capital investment and somewhat mired in inter-state/federal madness. Personally, I think privatizing the utility function was insane. There are some cool things which emerged after the 1970s grounded capital investment: High Voltag…

> And has two grids.

Not just two. There's also the Darwin/Katherine system which serves about 150k customers. The NWIS and Alice Springs system both have 20k+ customers. Australia has some really interesting power systems.

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

#30

Post by mindslight »

crmrc114 wrote: post #14
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…

Close, Three phase systems actually are a carry over from the days of early induction motors. Three phases can easily be connected to create a rotating magnetic field. We don't just use one phase at a time on the grid. All three are active. Phases A and B and C are all 120 degrees out of phase with each other. (That has nothing to do with the 120volts you know of in your house- it just happens to be another 120 numbe…

> Having AC power allows all kinds of cool things! Did you know that your common household 120v feed is simply a single phase being split into two 120v 'legs'. Both 120 degrees out of phase. So if you remember elementary school math the abs() of phase A at its peak of +120 and phase B at it's valley of -120 = 240.

The two legs are 180 degrees "out of phase" (that is to say one is simply the negative to the other). The peaks on each are +/- 170 volts, with a total peak across both of 340 volts. But we talk about AC in terms of RMS voltage, which is the DC-equivalent voltage that would perform the same work into a resistor, which is a factor of sqrt(2) for a sine wave, or "120/240 volts".

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