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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?

#41

Post by analog31 »

X6S1x6Okd1st wrote: post #10

> If you look at lists of the 100 greatest inventions of all time, electricity figures prominently. Once you get past some key enablers that can’t really be called inventions—fire, money, the wheel, calendars, the alphabet Well that's a doozy of a way to start. How is electricity an invention but those listed after are not?

Indeed, I was about to say that with electricity, we know when and by whom it was invented, but then again, the development of electricity as a useful power source was the work of multiple inventors over the span of decades. With those other inventions, possibly centuries, who knows. So I'd still call them inventions.

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

#42

Post by nemetroid »

nickff wrote: post #26
lutorm wrote: post #16

Earlier quoted context omitted.

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 smal…

No, one prong gets a phase and one prong gets the neutral, resulting in 230 V. Only equipment designed for 400 V gets two (or three) phases.

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

#43

Post by kazinator »

labcomputer wrote: post #34
crmrc114 wrote: post #14

Earlier quoted context omitted.

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…

> Close, Three phase systems actually are a carry over from the days of early induction motors. It's not just some historical accident. We continue to use multi-phase power because it enables continuous delivery of power (unlike single-phase, where the delivered power drops to zero at least twice per cycle). And two phases require just as many wires as three phases, with more power delivered for a given mass of coppe…

The advantage of three phase over two is that three phase can energize the coils of a three-phase motor so as to create a rotating magnetic field. No extra circuitry is needed.

Two-phase cannot do that when the phases are 180 degrees apart; opposite polarity is as good as a single phase. It would work if the two phases were 90 degrees apart.

A two-phase motor operating on single phase (or 180 degree two phase) needs to generate the 90 degree phase signal with extra circuitry.

Three phases is also smoother power delivery and even loading compared to two.

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

#44

Post by hyperdimension »

nickff wrote: post #27
crmrc114 wrote: post #14

Earlier quoted context omitted.

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, whic…

So does my...dishwasher. It actually generates three phase power (maybe stepped sine-wave?) for its main motor.

I did a double-take when I saw it (during the course of an unrelated fix,) considering it's powered off a simple (US) 120V 15-amp branch circuit.

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

#45

Post by gumby »

nickff wrote: post #26
lutorm wrote: post #16

Earlier quoted context omitted.

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 smal…

> but the disadvantage of increasing the risk if one is electrocuted.

Avoiding this was one of the design parameters of the "Schucho" plug design that is reasonably standard across Europe. You'll note the three prong plug has a longer ground that makes a connection before any hot one does. The US three prong is supposed to work that way too but the ground pin isn't long enough.

I continue to be amazed how many devices still ship with only two prong plugs (everywhere: Europe, North America, Australia...) even if those prongs are polarized.

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

#46

Post by labcomputer »

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 two phases of a three-phase supply.

From your car's or oven's perspective, it's still just single-phase power that happens to be floating w.r.t. ground.

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

#47

Post by dpierce9 »

At least part of the reason is regulatory. The national grid regulator (FERC) gets its foothold through the interstate commerce clause. Since Texas heavily restricts the interstate interconnections it is not regulated federally (or at least less regulated). Of course this doesn’t explain the East/west non-interconnection, I think historically the Rockies do most of that though (as the article mentions). The issue is only partially technical and largely administrative.

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

#48

Post by SECProto »

danielheath wrote: post #24
SECProto wrote: post #17

Earlier quoted context omitted.

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.

I mean, the reason I have never seen a wildfire is because they are exceedingly rare in my local biome. Nothing to do with artificial wildfire prevention.

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

#49

Post by imoverclocked »

The main point of this article has nothing to do with the technical details of power transportation and everything to do with politics and corruption of our academic/research institutions. It’s amazing how an anti-fact leader can have such corrupting influence on institutions that are building tomorrow’s leaders.

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

#50

Post by dylan604 »

gizmo385 wrote: post #40
danielheath wrote: post #24

Earlier quoted context omitted.

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

Given the record fire seasons in Colorado and California, not sure how well this comment reads.

It reads just fine. That particular individual has not seen wildfires in person. No need to read anything else into it.
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