6 ms·

Benefits of a single US electrical grid with high-voltage direct current

26 points by mbrubeck 11y ago

it_luddite 11y ago
Stopped reading at "while all the US grids operate on the same frequency, those frequencies aren't always aligned—the peak in the AC of one grid may line up with the trough in a neighboring grid". Practically every regional grid is interconnected to it's neighbor. If they get this basic infrastructure wrong, I'm unwilling to fact check the rest of their premise.
- mbrubeck 11y ago
  The article doesn't claim that interconnection is impossible, just that it requires extra AC->AC conversion hardware at each interface.
  - it_luddite 11y ago
    I didn't even read that far :0 The point of my comment was their lack of understanding of how the existing transmission system is connected to their neighboring regions. This is the base infrastructure of the electric energy market (long term, day ahead, and spot markets). These interconnects between regions (grids) requires that frequency is in synch and any deviation will cause a disconnect.
    - mikeash 11y ago
      My understanding is that there are five separate grids which are not frequency synchronized, as described here: https://en.wikipedia.org/wiki/Eastern_Interconnection https://en.wikipedia.org/wiki/Eastern_Interconnection They are connected, but with DC or other techniques that don't require matching phase. Not so?
  - VLM 11y ago
    https://en.wikipedia.org/wiki/Variable-frequency_transformer https://en.wikipedia.org/wiki/Variable-frequency_transformer VFTs are cool
digerata 11y ago
I was initially confused by the statement that direct current has lower transmission losses over long distances. My recollection was that a big argument for AC over DC going back to Edison v Tesla was that DC required DC generation centers all over the place because of transmission range: "The primary drawback with the Edison direct current system was that it ran at 110 volts from generation to its final destination giving it a relatively short useful transmission range: to keep the size of the expensive copper conductors down generating plants had to be situated in the middle of population centers and could only supply customers less than a mile from the plant." Source: https://en.wikipedia.org/wiki/War_of_Currents#Edison.27s_DC_company https://en.wikipedia.org/wiki/War_of_Currents#Edison.27s_DC_... Yet, it appears this is no longer the case. https://en.wikipedia.org/wiki/High-voltage_direct_current https://en.wikipedia.org/wiki/High-voltage_direct_current Why is that?
- mikeash 11y ago
  Because of the "high voltage." AC versus DC is not all that important by itself. What's important is transmitting electricity at high voltage. Transmission losses come from the amount of current you pass through a conductor. More current equals more power lost to the resistance of the conductor. Delivered electric power is equal to voltage multiplied by current. Higher voltage means lower current for the same amount of delivered power, which means lower transmission losses. The AC versus DC thing comes in because you need lower voltages for practical applications (it's hard to run a light bulb off 100kV) and that means you need to transform between different voltages. Transforming AC between different voltages is pretty easy: an AC transformer is basically just a pair of coils with a metal core, easily built with 19th-century technology. Transforming DC is much harder and requires much more advanced technology. For the 19th-century battle, this meant that AC was the only one that could be transmitted at extremely high voltages. DC was limited to serving very small areas because it had to be transmitted at the same voltages which would be used at the destinations. Today, that difference goes away, so the advantages and disadvantages are all about much smaller secondary effects instead.
  - deleted 11y ago
    [deleted]
neoCrimeLabs 11y ago
Thomas Edison's PR powerhouse still trying to make direct current look good and Nikola Tesla's alternating current look bad. When will the madness end? Note: This is meant as humor. :-)
cellularmitosis 11y ago
Currently, the electricity you get at home has been stepped down in voltage several times. The power station delivers it on the order of 100,000V, which gets stepped down at a sub-station to something like 20,000V, and then stepped down by a distribution transformer to 120/240V. If the grid were DC, what would do all of that stepping down? Is he proposing replacing all of those transformers with an army of industrial strength DC-DC converters? Wouldn't that eat into the efficiency gains he is proposing (I would also imagine that that gigantic active switching solutions are more expensive and less reliable than gigantic transformers). My first thought at a suggested alternative was "why not try increasing the frequency of the distribution AC?". This redditor explains why that's not ideal: https://www.reddit.com/r/askscience/comments/1u45rz/why_dont_we_use_a_higher_frequency_in_the_ac/ceejje6 https://www.reddit.com/r/askscience/comments/1u45rz/why_dont...
- SFjulie1 11y ago
  commutation would also be guaranteed (when circuits would be switched) to be highly funky and generating peaks with rebounds... in non linear ways. And with the multiplication of sources (wind/solar) commutation/switching are to be considered. A highly distributed system tends to be already chaotic. Adding chaos to chaos does not seem a good idea. Not to mention Biot Savart Law that says a long wire generates B ~= I/r So where the electric current on average nullifies the Magnetic field in AC (other a period), on DC you would have to build with a constant F = qv vect I/r which means a constant magnetic field appearing and inducing resilient constant forces for every other charges in movement. 1/r decrease way less than 1/r² // 1/r3. That is what CE norms on electro pollution wants to avoid. A strong electromagnetical residual signal that can interfere with other electromagnetic devices. I understand the concerns of persons that never had to learn electricity about the complexity of using Z (impedance) other R (resistance). But Fresnel law makes AC quite easy to grok. In some countries it is accepted since a long time that the bug in AC is the side effect of loosing the phase (hence introducing peaks up/down phase). That is the reason why companies have to pay not only for the whattage but also for the disruption of phase. Some companies even get discount to regulate the phases (like train companies that uses a lot of electricity in peak fashion at trains start/stop and can accumulate energy selectively to charge huge capacitors and use them to correct a shift of phase). I sometimes look at the electric cable in my cities. The way they are plugged anarchically and the transformers looking like not maintained, the electric boards with expensive gross protection, the corrosion at the connection points (yes surface effect with rust and water sure it does do weired loss) the fuse used in electricity/electronic devices .... And I feel like I was in Cuba in the 1986 in the middle of embargo. I don't live in Cuba, this I see in Montréal, SF, miami ... In supposed developed countries and I wonder if my eyes telling me it is broche à foin are right or my brain listening to all the assertive geeks and citizens telling me the opposite. You know what, I do not know. I still have a strong feeling technology on the new continent is not as good as it is publicized.
jonrx 11y ago
AFAIK Hydro-Quebec already does something like this. http://www.hydroquebec.com/learning/transport/grandes-distances.html http://www.hydroquebec.com/learning/transport/grandes-distan... Granted, there's not much details : « The technology used to transmit direct current is not the most common. However, it can be advantageous for isolating alternating-current systems or controlling the quantity of electricity transmitted. Hydro-Québec has a direct-current line (which goes from the Baie-James region to Sandy Pond, near Boston) as well as many direct-current interconnections with neighboring systems. »
Gravityloss 11y ago
China has built a lot of ultra high voltage AC and high voltage DC transmission lines, and is building more. http://dsius.com/cet/HVDCinChina_EPRI2013_HVDC.pdf http://dsius.com/cet/HVDCinChina_EPRI2013_HVDC.pdf There's been some cartels in the power transmission scene. http://www.reuters.com/article/eu-transformercartel-idUSL726781420091007 http://www.reuters.com/article/eu-transformercartel-idUSL726... It could be ripe for some "disruption".

26 points by mbrubeck 11y ago

Stopped reading at "while all the US grids operate on the same frequency, those frequencies aren't always aligned—the peak in the AC of one grid may line up with the trough in a neighboring grid". Practically every regional grid is interconnected to it's neighbor. If they get this basic infrastructure wrong, I'm unwilling to fact check the rest of their premise.

mbrubeck 11y ago
The article doesn't claim that interconnection is impossible, just that it requires extra AC->AC conversion hardware at each interface.
- it_luddite 11y ago
  I didn't even read that far :0 The point of my comment was their lack of understanding of how the existing transmission system is connected to their neighboring regions. This is the base infrastructure of the electric energy market (long term, day ahead, and spot markets). These interconnects between regions (grids) requires that frequency is in synch and any deviation will cause a disconnect.
  - mikeash 11y ago
    My understanding is that there are five separate grids which are not frequency synchronized, as described here: https://en.wikipedia.org/wiki/Eastern_Interconnection https://en.wikipedia.org/wiki/Eastern_Interconnection They are connected, but with DC or other techniques that don't require matching phase. Not so?
- VLM 11y ago
  https://en.wikipedia.org/wiki/Variable-frequency_transformer https://en.wikipedia.org/wiki/Variable-frequency_transformer VFTs are cool

digerata 11y ago

I was initially confused by the statement that direct current has lower transmission losses over long distances. My recollection was that a big argument for AC over DC going back to Edison v Tesla was that DC required DC generation centers all over the place because of transmission range: "The primary drawback with the Edison direct current system was that it ran at 110 volts from generation to its final destination giving it a relatively short useful transmission range: to keep the size of the expensive copper conductors down generating plants had to be situated in the middle of population centers and could only supply customers less than a mile from the plant." Source: https://en.wikipedia.org/wiki/War_of_Currents#Edison.27s_DC_company https://en.wikipedia.org/wiki/War_of_Currents#Edison.27s_DC_... Yet, it appears this is no longer the case. https://en.wikipedia.org/wiki/High-voltage_direct_current https://en.wikipedia.org/wiki/High-voltage_direct_current Why is that?

mikeash 11y ago
Because of the "high voltage." AC versus DC is not all that important by itself. What's important is transmitting electricity at high voltage. Transmission losses come from the amount of current you pass through a conductor. More current equals more power lost to the resistance of the conductor. Delivered electric power is equal to voltage multiplied by current. Higher voltage means lower current for the same amount of delivered power, which means lower transmission losses. The AC versus DC thing comes in because you need lower voltages for practical applications (it's hard to run a light bulb off 100kV) and that means you need to transform between different voltages. Transforming AC between different voltages is pretty easy: an AC transformer is basically just a pair of coils with a metal core, easily built with 19th-century technology. Transforming DC is much harder and requires much more advanced technology. For the 19th-century battle, this meant that AC was the only one that could be transmitted at extremely high voltages. DC was limited to serving very small areas because it had to be transmitted at the same voltages which would be used at the destinations. Today, that difference goes away, so the advantages and disadvantages are all about much smaller secondary effects instead.
- deleted 11y ago
  [deleted]

neoCrimeLabs 11y ago

Thomas Edison's PR powerhouse still trying to make direct current look good and Nikola Tesla's alternating current look bad. When will the madness end? Note: This is meant as humor. :-)

cellularmitosis 11y ago

Currently, the electricity you get at home has been stepped down in voltage several times. The power station delivers it on the order of 100,000V, which gets stepped down at a sub-station to something like 20,000V, and then stepped down by a distribution transformer to 120/240V. If the grid were DC, what would do all of that stepping down? Is he proposing replacing all of those transformers with an army of industrial strength DC-DC converters? Wouldn't that eat into the efficiency gains he is proposing (I would also imagine that that gigantic active switching solutions are more expensive and less reliable than gigantic transformers). My first thought at a suggested alternative was "why not try increasing the frequency of the distribution AC?". This redditor explains why that's not ideal: https://www.reddit.com/r/askscience/comments/1u45rz/why_dont_we_use_a_higher_frequency_in_the_ac/ceejje6 https://www.reddit.com/r/askscience/comments/1u45rz/why_dont...

SFjulie1 11y ago
commutation would also be guaranteed (when circuits would be switched) to be highly funky and generating peaks with rebounds... in non linear ways. And with the multiplication of sources (wind/solar) commutation/switching are to be considered. A highly distributed system tends to be already chaotic. Adding chaos to chaos does not seem a good idea. Not to mention Biot Savart Law that says a long wire generates B ~= I/r So where the electric current on average nullifies the Magnetic field in AC (other a period), on DC you would have to build with a constant F = qv vect I/r which means a constant magnetic field appearing and inducing resilient constant forces for every other charges in movement. 1/r decrease way less than 1/r² // 1/r3. That is what CE norms on electro pollution wants to avoid. A strong electromagnetical residual signal that can interfere with other electromagnetic devices. I understand the concerns of persons that never had to learn electricity about the complexity of using Z (impedance) other R (resistance). But Fresnel law makes AC quite easy to grok. In some countries it is accepted since a long time that the bug in AC is the side effect of loosing the phase (hence introducing peaks up/down phase). That is the reason why companies have to pay not only for the whattage but also for the disruption of phase. Some companies even get discount to regulate the phases (like train companies that uses a lot of electricity in peak fashion at trains start/stop and can accumulate energy selectively to charge huge capacitors and use them to correct a shift of phase). I sometimes look at the electric cable in my cities. The way they are plugged anarchically and the transformers looking like not maintained, the electric boards with expensive gross protection, the corrosion at the connection points (yes surface effect with rust and water sure it does do weired loss) the fuse used in electricity/electronic devices .... And I feel like I was in Cuba in the 1986 in the middle of embargo. I don't live in Cuba, this I see in Montréal, SF, miami ... In supposed developed countries and I wonder if my eyes telling me it is broche à foin are right or my brain listening to all the assertive geeks and citizens telling me the opposite. You know what, I do not know. I still have a strong feeling technology on the new continent is not as good as it is publicized.

jonrx 11y ago

AFAIK Hydro-Quebec already does something like this. http://www.hydroquebec.com/learning/transport/grandes-distances.html http://www.hydroquebec.com/learning/transport/grandes-distan... Granted, there's not much details : « The technology used to transmit direct current is not the most common. However, it can be advantageous for isolating alternating-current systems or controlling the quantity of electricity transmitted. Hydro-Québec has a direct-current line (which goes from the Baie-James region to Sandy Pond, near Boston) as well as many direct-current interconnections with neighboring systems. »

Gravityloss 11y ago

China has built a lot of ultra high voltage AC and high voltage DC transmission lines, and is building more. http://dsius.com/cet/HVDCinChina_EPRI2013_HVDC.pdf http://dsius.com/cet/HVDCinChina_EPRI2013_HVDC.pdf There's been some cartels in the power transmission scene. http://www.reuters.com/article/eu-transformercartel-idUSL726781420091007 http://www.reuters.com/article/eu-transformercartel-idUSL726... It could be ripe for some "disruption".