4 ms·

Doesn't electricity have a limit on how far it can be pushed through a wire? Looking for a little enlightenment on this topic.

dan_quixote 6y ago
Power loss is a function of current. So major transmission lines use very high voltage to lower the current (and thus the power loss). Of course, there are losses at the transformer(s) the step the voltage up and down. Unsurprisingly, it's a very use-case-dependent engineering problem.
briffle 6y ago
On the west coast of the US, we have a 3GW DC link between Portland (actually, The Dalles, a few miles from google's first datacenter) and Los Angeles. DC power transmission over long distances has less loss, and only requires 2 wires. Its 850 miles (about 1350km) https://en.wikipedia.org/wiki/Pacific_DC_Intertie https://en.wikipedia.org/wiki/Pacific_DC_Intertie
- pkulak 6y ago
  We ship all this renewable power to LA, and yet more than half my local (Portland) power makeup is coal.
  - asdff 6y ago
    Oh come one, that's small box thinking, you gotta look at the big picture. LA has a larger electricity demand than portland and it oscillates in a different pattern than portland. In the summer, due to AC, LA needs more peak capacity. However in the winter, the equation flips and now Portland needs that capacity to heat homes. Keeping all that hydro in washington to support the comparitively teensy population of 650k in portland is a waste, especially when demand is needed down south and not in the north and vice versa; this line serves 3 million in LA and represents half the LADWP peak capacity. I'd argue cutting LA off would force more coal plants to open than what is needed to electrify portland today.
    - d4mi3n 6y ago
      Fantastic and valid points, though I think pkulak also has a fair point in identifying that this big picture setup negatively impacts folks in Portland via air pollution and other side effects of more coal plants than would otherwise be required.
      - asdff 6y ago
        On the other hand, that energy has to come from some place and this set up negatively impacts someone no matter where the coal plant is located. Maybe the coal comes from the cascades and it makes more sense to put the plant close to the source, rather than somewhere near LA and have to freight in the coal from the mines and deal with those externalities that might be worse than simply running a wire to LA.
    - pkulak 6y ago
      You misunderstood me a bit, though I was pretty vague. I was just remarking on how we have enough local, renewable power locally, and yet burn coal. We could easily get our power from hydro AND send the majority to LA, but instead we don't. Probably because LA is willing to pay so much more for it.
      - dan_quixote 6y ago
        I don't know the political climate in Oregon about hydro, but it's starting to turn a bit in Washington. Dams are pretty awful for salmon and so much of our ecology is salmon-based as well as the culture/livelihoods of Native Americans. The biggest story in recent years was the Elwha dam removal. It's stunning to see how much the landscape has changed since: https://therevelator.org/elwha-dam-removal/ https://therevelator.org/elwha-dam-removal/ And a recent story about a Skagit river dam: https://www.king5.com/article/news/investigations/seattles-skagit-river-dams-hurt-salmon-orcas-and-native-american-culture-agencies-say/281-d4e483c2-1178-4af1-b8db-634e3b4009f7 https://www.king5.com/article/news/investigations/seattles-s...
        xxpor 6y ago
pkulak 6y ago
Not really. The higher the volts, the fewer amps and losses. So, if you can just get the voltage high enough, there's really no limit. Not sure what the current highest volt transmissions are. Maybe a couple million volts on some DC lines? But I think that's good enough for hundreds, if not thousands, of miles of efficient transmission.
MayeulC 6y ago
Not really, that limit is only due to the wire resistance, which goes down with wire thickness. There will be a delay of course, which is the cable impedance (inductance), mostly due to the speed of electricity not being infinite in a conductor. A bit like there is no limit for the length of a stick you can push with your arm. There's only resistance if it's on the ground (push it in space to visualize a superconductor). It also has inertia (mass, which is inductance). And at longer lengths, you won't see the end move before the movement you impulsed has reached the end at ~the speed of sound in that material. Now, to go a bit into the details: A/C can also exploit "skin effect" where a high frequency A/C signal only travels on the outside of conductors. That way, you can make thinner conductors (just coat regular cables in an expensive conductor)... Up to a certain point, since if you need to carry more power, you need extra large cables, hollow ones, and/or multiple cables). That wastes part of the conductor: https://en.wikipedia.org/wiki/Skin_effect https://en.wikipedia.org/wiki/Skin_effect With A/C, you can also use transformers, but not with D/C, which has traditionally been an hindrance to high-voltage DC. You have to generate alternative current, or use boost circuits (basically charge a capacitor at constant current to increase voltage). Cutting power in high-power A/C is simpler, since you can do it when voltage crosses 0 V. I'm not sure what the pros and cons of both are when it comes to economics. It seems D/C is getting more affordable thanks to semiconductors: https://en.wikipedia.org/wiki/High-voltage_direct_current#Advantages https://en.wikipedia.org/wiki/High-voltage_direct_current#Ad...

dan_quixote 6y ago

Power loss is a function of current. So major transmission lines use very high voltage to lower the current (and thus the power loss). Of course, there are losses at the transformer(s) the step the voltage up and down. Unsurprisingly, it's a very use-case-dependent engineering problem.

briffle 6y ago

On the west coast of the US, we have a 3GW DC link between Portland (actually, The Dalles, a few miles from google's first datacenter) and Los Angeles. DC power transmission over long distances has less loss, and only requires 2 wires. Its 850 miles (about 1350km) https://en.wikipedia.org/wiki/Pacific_DC_Intertie https://en.wikipedia.org/wiki/Pacific_DC_Intertie

pkulak 6y ago
We ship all this renewable power to LA, and yet more than half my local (Portland) power makeup is coal.
- asdff 6y ago
  Oh come one, that's small box thinking, you gotta look at the big picture. LA has a larger electricity demand than portland and it oscillates in a different pattern than portland. In the summer, due to AC, LA needs more peak capacity. However in the winter, the equation flips and now Portland needs that capacity to heat homes. Keeping all that hydro in washington to support the comparitively teensy population of 650k in portland is a waste, especially when demand is needed down south and not in the north and vice versa; this line serves 3 million in LA and represents half the LADWP peak capacity. I'd argue cutting LA off would force more coal plants to open than what is needed to electrify portland today.
  - d4mi3n 6y ago
    Fantastic and valid points, though I think pkulak also has a fair point in identifying that this big picture setup negatively impacts folks in Portland via air pollution and other side effects of more coal plants than would otherwise be required.
    - asdff 6y ago
      On the other hand, that energy has to come from some place and this set up negatively impacts someone no matter where the coal plant is located. Maybe the coal comes from the cascades and it makes more sense to put the plant close to the source, rather than somewhere near LA and have to freight in the coal from the mines and deal with those externalities that might be worse than simply running a wire to LA.
  - pkulak 6y ago
    You misunderstood me a bit, though I was pretty vague. I was just remarking on how we have enough local, renewable power locally, and yet burn coal. We could easily get our power from hydro AND send the majority to LA, but instead we don't. Probably because LA is willing to pay so much more for it.
    - dan_quixote 6y ago
      I don't know the political climate in Oregon about hydro, but it's starting to turn a bit in Washington. Dams are pretty awful for salmon and so much of our ecology is salmon-based as well as the culture/livelihoods of Native Americans. The biggest story in recent years was the Elwha dam removal. It's stunning to see how much the landscape has changed since: https://therevelator.org/elwha-dam-removal/ https://therevelator.org/elwha-dam-removal/ And a recent story about a Skagit river dam: https://www.king5.com/article/news/investigations/seattles-skagit-river-dams-hurt-salmon-orcas-and-native-american-culture-agencies-say/281-d4e483c2-1178-4af1-b8db-634e3b4009f7 https://www.king5.com/article/news/investigations/seattles-s...
      - xxpor 6y ago

pkulak 6y ago

Not really. The higher the volts, the fewer amps and losses. So, if you can just get the voltage high enough, there's really no limit. Not sure what the current highest volt transmissions are. Maybe a couple million volts on some DC lines? But I think that's good enough for hundreds, if not thousands, of miles of efficient transmission.

MayeulC 6y ago

Not really, that limit is only due to the wire resistance, which goes down with wire thickness. There will be a delay of course, which is the cable impedance (inductance), mostly due to the speed of electricity not being infinite in a conductor. A bit like there is no limit for the length of a stick you can push with your arm. There's only resistance if it's on the ground (push it in space to visualize a superconductor). It also has inertia (mass, which is inductance). And at longer lengths, you won't see the end move before the movement you impulsed has reached the end at ~the speed of sound in that material. Now, to go a bit into the details: A/C can also exploit "skin effect" where a high frequency A/C signal only travels on the outside of conductors. That way, you can make thinner conductors (just coat regular cables in an expensive conductor)... Up to a certain point, since if you need to carry more power, you need extra large cables, hollow ones, and/or multiple cables). That wastes part of the conductor: https://en.wikipedia.org/wiki/Skin_effect https://en.wikipedia.org/wiki/Skin_effect With A/C, you can also use transformers, but not with D/C, which has traditionally been an hindrance to high-voltage DC. You have to generate alternative current, or use boost circuits (basically charge a capacitor at constant current to increase voltage). Cutting power in high-power A/C is simpler, since you can do it when voltage crosses 0 V. I'm not sure what the pros and cons of both are when it comes to economics. It seems D/C is getting more affordable thanks to semiconductors: https://en.wikipedia.org/wiki/High-voltage_direct_current#Advantages https://en.wikipedia.org/wiki/High-voltage_direct_current#Ad...