Why Does the U.S. Have Three Electrical Grids?
spectrum.ieee.org
spectrum.ieee.org
Like, did Japanese companies actually invent inverters, or are inverter air conditioners more common in Japan compared to other countries?
Here's Daikin's argument (japanese). Green is % of inverter and Japan is 100%.
https://www.daikin.co.jp/csr/information/lecture/act01.html
https://www.daikin.co.jp/csr/information/lecture/images/act0...
It seems that world's first inverter a/c is by Toshiba.
https://toshiba-mirai-kagakukan.jp/en/learn/history/ichigoki...
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.
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..
Political tension between Serbia and Kosovo is not entirely unexpected of course, but it's weird if that starts affecting clocks half a continent away.
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 Voltage DC is very cool. Avoids some of the issues of phase and load mis-alignment between regions, generation models.
Arguments for a different kind of net exist. More local resiliency. More load shedding, more respect for home solar and batteries, as well as storage in the network.
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.
in the top end, fruitbats and cyclonic storms are common disruptions
its got better in the suburbs since lotsa wires went underground, but just a few km down the highway and the grade of service drops.
It seems to be both overinvested and underinvested? How can it be both? (Sorry looking for insight not trying to disprove what you say)
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.)
Folks may not realize that power is transmitted in three phases in the US. AC power is essentially a sin wave, and we use 3 different 'phases', which are just shifted sin waves so that we basically always have at least one phase providing power at any time.
Every generator hooked up to the grid must be synchronized to the same 60 hz phases. There are devices called 'phasors' that assist in ensuring generators are lined up with the grid. And now there are networked versions to help coordinate across large regions.
But if two grids are on different phases, then there will be serious problems in connecting them together -- mostly that generators will be fighting against each other and potentially causing damage to things on the grid expecting clean 60hz power. It gets complicated pretty quickly.
AC has inductive properties. I.e. it can induce electrical currents in wires across a core. (Transformer) DC cannot do this. Before vacuum tubes and other tech AC was one of the few technologies that could be easily stepped up to hundreds of thousands of volts.
Voltage and current have an inverse relationship. So we can step up voltage and reduce the size of the conductor $$$$ other feature is reduced line losses (HVDC actually beats us here but this is another discussion)
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.
It gets better! We can be cheap on wire with AC systems! I can wire a 'multiwire branch circuit'. With phases a and b that share a neutral. If the current on phase a is 20 amps and the current on phase B is 20 amps what is the return current on my neutral? ( Google Mike Holt Multiwire Branch, Enjoy )
Want more fun. Read about Neutral Earth Voltage and NFPA 70 requirements for agriculture and equipotential planes. :-)
AC is freaking magical. The grid is even more awesome!
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 copper and insulation, so... we use three.
> If the current on phase a is 20 amps and the current on phase B is 20 amps what is the return current on my neutral?
That depends on the (complex) impedance in each branch. In the pathological case, the current on the neutral could be as high as 40 Amps.
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.
In hindsight I did not specify circut ampacity, or wire gauge. Still the question stands, how much current would you read at the panel on the neutral with those two loads on the line :-)
(In my example you have two phases 120 degrees apart. Think US Residential split phase. The actual result is pretty awesome. It's a common test problem for new electricians.)
I won't spoil the result because it's too cool when you get it.
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.
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.
Three phase is better than one for transmission: you can pass more power for a given distance with a given budget of copper/aluminium wire. In other words, you have three wires rather than 2, but they can be lighter overall, and require less materials and fewer and less expensive poles.
I think you mean 180 degrees out of phase.
Most houses in the US have 240V service for large loads like A/C, ovens, stoves, dryers, EV chargers, etc. The way you get 240V (in the US) is that you take a single phase, and apply it to a transformer. The transformer's secondary has a grounded center tap, so you get +/- 120V, 180 degrees out of phase (this is called "split phase").
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".
> Steven Cherry So barely one-tenth of one percent.
From TFA.
Anything you can find to support grid interconnects as black-start capacity?
From what I understand there can be a number of different techniques for black starting a grid, including pumped storage / hydro generation because they can be started with very modest power. Being able to jumpstart a grid based off of a neighbouring grid seems to make sense.
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.
https://en.m.wikipedia.org/wiki/Synchronous_grid_of_Continen...
This might counter the grandparent poster if Asia was on the same synchronous grid, but it's not.
Here's the map including all larger powerlines
It spans 8 timezones.
Europe is just larger in capacity, not breadth.
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 difference between the phases (for their higher-voltage loads).
Now, if you've ever looked at an oven or a dryer (in North America at least), you'll know that they are higher voltage, and look like they are two-phase... But it's really more like one phase that's been mirrored.
Here's a nice diagram: https://electronics.stackexchange.com/questions/146420/obtai...
I am not an electrician or EE. I just spent a bunch of time looking into this when I got my 240v table saw and had to hook it up to something.
As proof that I'm not totally bullshitting you: until recently our house had a 120v outlet on a 240v breaker for a baseboard radiator. The electrician was here to fix an unrelated issue, and rejiggered things in the panel to hook it up to a 120v breaker.
As far as I understand it (not very) there is no such thing as two-phase power.
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.
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.
From your car's or oven's perspective, it's still just single-phase power that happens to be floating w.r.t. ground.
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.
(It's as if the US grid characteristics were decided by the copper vendors... ;-)
It was designed without an issue with copper usage. Europe had very little development and quit a bit of rationing while building out the grid post-WW2. The US had no such issue and spent no time working within those constraints.
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.
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.
Because most devices these days have plastic cases (Class II double insulated), so there's nothing metal to touch to get shocked even in the case of a fault. That coupled with how GFCI/RCDs are being widely adopted as well leads to grounding not being as important.
Meanwhile I'm sitting 2 feet away from a nearly completely metal lamp with a two-prong plug.
The US is 120V, or split-phase 240 V. Depending where you are, it's allowed to be ±5% at the meter. NEC guidelines say no more than 3% voltage drop from there.
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.
This means it's impossible to synchronize the entire grid. The synchronization depends on the length of the path across the US.
I'm not sure actually how they propose to deal with this.
Edit, found this: https://news.ycombinator.com/item?id=16536121
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
No there won't. The article mentions DC power converters. They are not cheap, but since HV DC lines are better for long distance power transmission than three phase AC, it's killing two birds with one stone.
With high power systems it might not be practical to do it with a single capacitor or inductor but it still can be done.
https://youtube.com/watch?v=HqZtptHnC2I
(Substation complexity.)
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.)
But it's a fair point regarding the political influence in these type things, though it's not just the current administration. In a couple of months we will all be changing the verbiage of our proposals from resiliency, security back to renewable integration to satisfy our funding overlords.
Not saying a unified grid is not worth it, but there are downsides that might not be immediately obvious.
Hopefully we have gotten a bit better and stockpile spares for critical infrastructure such as the electrical grid, especially when we have lost so much of our internal manufacturing capabilities.
Transformers that are small are often on hand and easy to swap out. But some of the bigger ones have months long lead times. The facility we were at had transformers that had a 6 month lead time from Germany to replace them and they had to be sent via boat as they wouldn’t fit in planes.
"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.
The reason why AC is taught as being "more efficient" is that if you use AC you can easily use a transformer to increase the voltage (decrease the current) of the electricity being transported. That makes the transport more efficient because of I²R power losses. The reason why AC is "easier" to transform is because the classical transformer (two coils of wire and a laminated iron core -- no moving parts and incredibly efficient) requires AC input. Most power grids do use AC because this makes the grid much simpler to produce and
However the part that is missing from high-school education is that AC travelling down power lines at the same voltage as DC is less efficient and more expensive per kilometre. There are many reasons for this -- but the main ones are that the skin effect means AC current only travels on the outer parts of a wire causing higher current density and thus higher losses, the generation of RF interference, and the fact that AC lines have to transport reactive power (AC current reverses direction every half-cycle which essentially means more power loss).
So the most efficient transport mechanism for long distances is to generate AC, transform it up to a high voltage, and then rectify it to DC for the actual transport (and reverse the procedure on the other side). However the rectification procedure requires expensive equipment, which is why HVDC transport is only used for long-distance power transportation.
However, since the 1930s we’ve been able to build high voltage DC lines, and costs have plummet in the last 30-40 years (as we moved away from Hg rectifier tubes to Si high power electronics).
DC has many advantages:
- No capacitive coupling to ground - No reflections due to Z mismatch - You can lay a cable underwater (basically impossible with AC) - you can connect incompatible grids
HVDC is still fairly expensive (obviously compared to a lump of laminated steel) so it’s used for very long lines, or other special needs.
But it’s revolutionized the field.
AC still has many advantages and won’t go anywhere, especially last-mile to medium range:
- arguably safer since an arc fault can self extinguish - switches are much cheaper to build - cheap electric motors - cheap ability to scale V
DC current is more efficiently transmitted (conducted) over long distances at high voltage.
Since the early 20th century, DC transformers have become more efficient, as others have noted.
Given that electric grid transmission occurs at a wide range of voltages (~275kV generation, ~100kV long distance, 50kV local, 110/220V residential/commercial drops), efficient, reliable, cheap transformers were required, giving the initial edge to AC.
The one thing that pushes people into DC is that phase synchronization is a huge problem on high voltage. So, for indirect reasons, DC gets to be the winner right now.
What do you mean by that? My understanding is the HVDC lines are still lower V than an AC line (the Soviet even had 500lV lines), and therefore DCs advantages are no coupling to ground, no Z reflections and ability to connect to any grid.
> Most HVDC links use voltages between 100 kV and 800 kV.
By contrast, high voltage AC lines are around 10kV to (very rarely) 100kV. AC presents some more problems to high voltage than just phase synchronization (so even two point lines are DC), but the gains come mostly from the HV part, and AC is avoided because it doesn't play well with HV, reverting the gains.
Nowadays, a lot of residential loads at least would probably be more efficient with DC coming into the house with the popularization off brushless DC motors and all the technology around the house.
https://en.wikipedia.org/wiki/Traction_power_network
https://de.wikipedia.org/wiki/Bahnstromnetz#/media/Datei:Bah...
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)
https://en.wikipedia.org/wiki/North_American_power_transmiss...
This isn't a useful thought experiment. What was the author thinking?
How about no? Centralization means single point of failure. If anything we need more, smaller, localized grids that are reactive to their localized needs.
(It can also be lossy, as the atoms are small enough to leak through metals, causing hydrogen embrittlement along the way)
Any idea what the author means by this?
Why east and west are separate is probably more interesting.
Well that's a doozy of a way to start. How is electricity an invention but those listed after are not?
The others, though, are certainly inventions.
And magnets certainly do occur naturaly, and so does nuclear fission and fusion.
Electricity is not the same as electric power, just as nuclear fission is not the same as a nuclear weapon, just the same as fire is not the same as a coal fired power plant.
Electricity and nuclear fission were discovered, not invented.
I stumbled over that comment as well, though the article doesn't hinge on it.