Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

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

spectrum.ieee.org

Post reply on HN
Print view View original

51–60 of 155 posts

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

#51

Post by nickff »

labcomputer wrote: post #46
nickff wrote: post #36

Earlier quoted context omitted.

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.

Well, it would be the same as single-phase power (to the device) if the devices were not connected to the neutral. The oven actually takes one of the phases (along with the neutral), and uses it to power some accessories.

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

#52

Post by CameronNemo »

imoverclocked wrote: post #49

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.

I've flagged the article for such a reason.

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

#53

Post by URSpider94 »

hyperdimension wrote: post #44
nickff wrote: post #27

Earlier quoted context omitted.

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.

Almost all modern motors use inverter circuits to generate multi-phase drive signals. Any time you see a product with a “brushless motor”, that’s what it means.

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

#54

Post by URSpider94 »

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…

You mention the challenge with connecting out-of-phase grids. This is I believe why the proposed interconnects are high-voltage DC, as mentioned in the article. Power will be loaded in from one AC system, transported, and then offloaded as AC properly synchronized to the recipient grid.

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

#55

Post by swatson741 »

The article makes this seem like it's a US problem but, the interconnects lay in Canada and Mexico too. I'm guessing that unification is a low priority for them since it seems that the US stands to gain the most from it.

"DC power lines transmit power more efficiently than AC lines do"

This is not at all what is taught at school. Looking into this is interesting. 100 years ago people were debating about whether AC or DC is a better means of transmitting power and, it looks like answers still aren't clear now. I'm interested in knowing what an expert in this thinks.

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

#56

Post by 8bitsrule »

Worth mentioning here that China has massively invested in HVDC for over a decade (and still is [0] ... about a half-trillion/year lately).

The longer that N.A. drags its heels on this, the longer it'll take to move to renewables. (Just another infrastructure need that might have been paid for by funds thrown into Forever War.)

[0] https://www.youtube.com/watch?v=rThkjp-bp8M "China's MILLION VOLT Energy Superhighway" (12m)

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

#57

Post by toast0 »

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…

> Don't ask me how grounding works for 240v appliances. I have no idea.

Ground is 'the same' for 240v and 120v on split phase. A usually bare copper wire is run from the ground pin to the service panel, in the main service panel ground and neutral are connected together and to the utility neutral and the grounding rod.

Most 240v outlets are hot-hot-ground, or hot-hot-neutral-ground; some older outlets were hot-hot-neutral and the appliance was supposed to be wired separately to ground (and we can all suppose how often that was done properly, resulting in that outlet type becoming disfavored).

I'm currently rejiggering a 240v wired box for 120v outlets, after finding the wires in the panel and confirming they don't power any other 240v outlets, I'm connecting the white wire to the neutral bus bar, and the black wire to a spare 120v breaker, and then it's normal wiring of the outlet.

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

#58

Post by ggm »

siddboots wrote: post #29
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.

Sorry I didn't capture that. I bet the NT gets better service outcomes than either WA or east coast, sooner (because more focussed)

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

#59

Post by ggm »

rbg246 wrote: post #23
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)

Gold plating is a bit of a misnomer. Capital investment made in transmission was assured a rate of return above CPI. It was a gold class, form of spending money to earn future revenue under regulation. They didn't invest in the parts which we need now, in the light of shifts in transmission models from Coal and Gas, to both inter-state dependencies on trunks, and the in-local-distribution network storage and generation. They chose to invest in the assets they had, which were not the ones we need to invest in, to cope with variable load in wind and solar, and distributed generation in the home.

Demand management, variable load, need for Syncons and storage and need for more resiliency in the inter-state connections and the "rhombus of regret" are where money needs to go.

the gold plating was not made there. And in any case, its rent-seeking behaviour: its not a good model.

(this is highly subjective opinion btw. A good economist to read on this is John Quiggin, and a good alternative engergy advocate is Giles Parkinson, reneweconomy. They are also partisan, but knowledgeable.)

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

#60

Post by mauvehaus »

nickff wrote: post #51
labcomputer wrote: post #46

Earlier quoted context omitted.

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.

Well, it would be the same as single-phase power (to the device) if the devices were not connected to the neutral. The oven actually takes one of the phases (along with the neutral), and uses it to power some accessories.

With the massive caveat that I don't have a first principles understanding of any of this: I don't thing any individual load in your oven takes both legs and the neutral to do work. They're all either 120v or 208v single phase.

Aside: a lot of motors can run on either 240v single phase or 208v single phase (or, presumably, anything in between?). Take a look at Grainger or McMaster-Carr.

Post reply on HN