8 ms·

> 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

> 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 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.

aidenn0 6y ago
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?
- samcheng 6y ago
  It's a lot of current, so maybe you want superconducting HVDC: https://en.wikipedia.org/wiki/Tres_Amigas_SuperStation https://en.wikipedia.org/wiki/Tres_Amigas_SuperStation
  - msisk6 6y ago
    Last I heard the whole Tres Amigas SuperStation deal totally fell apart.
- msisk6 6y ago
  That's exactly right, but the capacity is limited. ERCOT in Texas, for example, has 5 DC ties to the other grids: http://www.ercot.com/content/cdr/html/real_time_system_conditions.html http://www.ercot.com/content/cdr/html/real_time_system_condi...
  - 7thaccount 6y ago
    Most of them are ageing too.
  - dredmorbius 6y ago
    > Peter Fairley: So to give you a sense of just what the scale of the transfers is and how small it is, the East and the West interconnects have a total of about 950 gigawatts of power-generating capacity together. And they can share a little over one gigawatt of electricity. > Steven Cherry So barely one-tenth of one percent. From TFA.
    - VBprogrammer 6y ago
      I wonder if this has more to do with "Black Start" planning than actually providing power cross grids. https://en.wikipedia.org/wiki/Black_start https://en.wikipedia.org/wiki/Black_start
      - dredmorbius 6y ago
        Interesting suggestion, though AFAIK that typically relies on auxiliary onsite power source at some generating plants, as noted in the Wikipedia article intro? Anything you can find to support grid interconnects as black-start capacity?
        VBprogrammer 6y ago
        Purely speculation based on the small capacity compared to total generated 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.
- jdswain 6y ago
  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.
  - tinix 6y ago
    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...
    - Gwypaas 6y ago
      Apparently not a problem to do today. https://en.m.wikipedia.org/wiki/Synchronous_grid_of_Continental_Europe https://en.m.wikipedia.org/wiki/Synchronous_grid_of_Continen...
      - phonethrowaway 6y ago
        That's not a very large area, to be fair. That's about the size of half of the United States, in distance/spread. Europe isn't a continent in the traditional sense, it's a region, and not a huge one. This might counter the grandparent poster if Asia was on the same synchronous grid, but it's not.
        Gwypaas 6y ago
        I guess there's two ways of looking at it. The distances spanned by the extreme points net or how dense it is. Not that I have the knowledge to relate any of that to real world use cases or consequences. Here's the map including all larger powerlines https://www.entsoe.eu/data/map/ https://www.entsoe.eu/data/map/
      - phonethrowaway 6y ago
        This is a better example IMO: https://en.wikipedia.org/wiki/IPS/UPS https://en.wikipedia.org/wiki/IPS/UPS It spans 8 timezones. Europe is just larger in capacity, not breadth.
- taneq 6y ago
  Pretty much. I mean, that's basically what a VSD is: A 3-phase rectifier back to back with a 3-phase inverter. Then you can have the two sides at different voltages and phases and transfer power back and forth at will.
nickff 6y ago
>"[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 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/obtaining-240v-from-480v-3-phase https://electronics.stackexchange.com/questions/146420/obtai...
- mauvehaus 6y ago
  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 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.
  - JdeBP 6y ago
    Enjoy https://youtu.be/jMmUoZh3Hq4 https://youtu.be/jMmUoZh3Hq4 .
  - nickff 6y ago
    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.
gerdesj 6y ago
"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.)
- lutorm 6y ago
  "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.
  - mauvehaus 6y ago
    They're also self starting and trivially reversible. Single phase motors require a separate starting arrangement.
ars 6y ago
The speed of light is an issue as well - it takes about 1/60 of a second to cross the US. 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 https://news.ycombinator.com/item?id=16536121
crmrc114 6y ago
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 number) 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!
- ghouse 6y ago
  > 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. I think you mean 180 degrees out of phase.
  - labcomputer 6y ago
    It's not clear what he meant (because this part doesn't really have anything to do with 3-phase), but: 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").
hristov 6y ago
I am not sure what your point is. It is possible to change the phase of a signal. In fact, a simple capacitor or inductor will do it. With high power systems it might not be practical to do it with a single capacitor or inductor but it still can be done.
URSpider94 6y ago
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.
dredmorbius 6y ago
Interesting explainer: Why 3 Phase Power? Why not 6 or 12? https://youtube.com/watch?v=HqZtptHnC2I https://youtube.com/watch?v=HqZtptHnC2I (Substation complexity.)
- jhoechtl 6y ago
  And reduced efficiency
- kozak 6y ago
  I like the minimalistic explanation that it's because two phases are not enough and four phases are too many.
himinlomax 6y ago
> then there will be serious problems in connecting them together 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.
Shivetya 6y ago
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 https://youtu.be/HqZtptHnC2I

aidenn0 6y ago

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?

samcheng 6y ago
It's a lot of current, so maybe you want superconducting HVDC: https://en.wikipedia.org/wiki/Tres_Amigas_SuperStation https://en.wikipedia.org/wiki/Tres_Amigas_SuperStation
- msisk6 6y ago
  Last I heard the whole Tres Amigas SuperStation deal totally fell apart.
msisk6 6y ago
That's exactly right, but the capacity is limited. ERCOT in Texas, for example, has 5 DC ties to the other grids: http://www.ercot.com/content/cdr/html/real_time_system_conditions.html http://www.ercot.com/content/cdr/html/real_time_system_condi...
- 7thaccount 6y ago
  Most of them are ageing too.
- dredmorbius 6y ago
  > Peter Fairley: So to give you a sense of just what the scale of the transfers is and how small it is, the East and the West interconnects have a total of about 950 gigawatts of power-generating capacity together. And they can share a little over one gigawatt of electricity. > Steven Cherry So barely one-tenth of one percent. From TFA.
  - VBprogrammer 6y ago
    I wonder if this has more to do with "Black Start" planning than actually providing power cross grids. https://en.wikipedia.org/wiki/Black_start https://en.wikipedia.org/wiki/Black_start
    - dredmorbius 6y ago
      Interesting suggestion, though AFAIK that typically relies on auxiliary onsite power source at some generating plants, as noted in the Wikipedia article intro? Anything you can find to support grid interconnects as black-start capacity?
      - VBprogrammer 6y ago
        Purely speculation based on the small capacity compared to total generated 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.
jdswain 6y ago
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.
- tinix 6y ago
  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...
  - Gwypaas 6y ago
    Apparently not a problem to do today. https://en.m.wikipedia.org/wiki/Synchronous_grid_of_Continental_Europe https://en.m.wikipedia.org/wiki/Synchronous_grid_of_Continen...
    - phonethrowaway 6y ago
      That's not a very large area, to be fair. That's about the size of half of the United States, in distance/spread. Europe isn't a continent in the traditional sense, it's a region, and not a huge one. This might counter the grandparent poster if Asia was on the same synchronous grid, but it's not.
      - Gwypaas 6y ago
        I guess there's two ways of looking at it. The distances spanned by the extreme points net or how dense it is. Not that I have the knowledge to relate any of that to real world use cases or consequences. Here's the map including all larger powerlines https://www.entsoe.eu/data/map/ https://www.entsoe.eu/data/map/
    - phonethrowaway 6y ago
      This is a better example IMO: https://en.wikipedia.org/wiki/IPS/UPS https://en.wikipedia.org/wiki/IPS/UPS It spans 8 timezones. Europe is just larger in capacity, not breadth.
taneq 6y ago
Pretty much. I mean, that's basically what a VSD is: A 3-phase rectifier back to back with a 3-phase inverter. Then you can have the two sides at different voltages and phases and transfer power back and forth at will.

nickff 6y ago

>"[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 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/obtaining-240v-from-480v-3-phase https://electronics.stackexchange.com/questions/146420/obtai...

mauvehaus 6y ago
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 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.
- JdeBP 6y ago
  Enjoy https://youtu.be/jMmUoZh3Hq4 https://youtu.be/jMmUoZh3Hq4 .
- nickff 6y ago
  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.

gerdesj 6y ago

"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.)

lutorm 6y ago
"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.
- mauvehaus 6y ago
  They're also self starting and trivially reversible. Single phase motors require a separate starting arrangement.

ars 6y ago

The speed of light is an issue as well - it takes about 1/60 of a second to cross the US. 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 https://news.ycombinator.com/item?id=16536121

crmrc114 6y ago

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 number) 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!

ghouse 6y ago
> 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. I think you mean 180 degrees out of phase.
- labcomputer 6y ago
  It's not clear what he meant (because this part doesn't really have anything to do with 3-phase), but: 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").

hristov 6y ago

I am not sure what your point is. It is possible to change the phase of a signal. In fact, a simple capacitor or inductor will do it. With high power systems it might not be practical to do it with a single capacitor or inductor but it still can be done.

URSpider94 6y ago

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.

dredmorbius 6y ago

Interesting explainer: Why 3 Phase Power? Why not 6 or 12? https://youtube.com/watch?v=HqZtptHnC2I https://youtube.com/watch?v=HqZtptHnC2I (Substation complexity.)

jhoechtl 6y ago
And reduced efficiency
kozak 6y ago
I like the minimalistic explanation that it's because two phases are not enough and four phases are too many.

himinlomax 6y ago

> then there will be serious problems in connecting them together 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.

Shivetya 6y ago

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 https://youtu.be/HqZtptHnC2I