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Transmission line energy loss/length.

  1. Sep 15, 2013 #1
    Here are some figures from this article.
    Wiki: Electric Power Transmission
    Unless I made a mistake, that would be approximately 100W to 200W loss per foot.
    That's some 6 to 13 times as much as the percentage loss in the example above, but it doesn't tell me what is the line length or energy transmitted. Does anyone know what is the number of Watts lost per foot (or the same thing in any other units) for typical real transmission lines?
  2. jcsd
  3. Sep 16, 2013 #2


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    I get different numbers. 1% of 1000MW is 10MW and 100 miles is 528000 feet. More like 20W per foot.

    Also, it is 1000MW of POWER.
  4. Sep 16, 2013 #3
    You're right. It's because I entered 10GW instead of 1GW in my calculator and didn't check the result. But is 20 Watts a typical real world number? It uses a figure of 1.1% for the power loss instead of the average 6.5%.
  5. Sep 16, 2013 #4

    jim hardy

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  6. Sep 16, 2013 #5
    The wiki link I provided said 6.5% and the article you linked to said 6.8%. The 3% figure you a referring seems to be just the resistance loss, or just the corona loss. But none of this answers my question.
  7. Sep 17, 2013 #6

    jim hardy

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    I take it the question was:
    from the Stanford.edu link above,
    4mw/100 miles sounds like ~7.57 watts/foot. Remember there's three wires.
    Perhaps there's a genuine power systems guy somewhere on the forum who'd have a better suggestion.
  8. Sep 17, 2013 #7
    The problem with the 7.5 Watts per foot figure that you calculated is that it was for a configuration in which the loss was roughly 2.5%. I also calculated the loss per foot for a configuration given in the wiki article. However, from both articles we know that the average loss is 6.5%. The problem with the 6.5% figure is that we don't know the configuration. It is easy to get the loss per foot for an example configuration, but what is the loss per foot for a typical (6.5% loss) configuration.

    To give a concrete example of what I mean, take these figures from the Stanford link:
    That's .4% loss. Since the average loss is 6.5%, this is not a typical situation. 6.4/.4 = 16 so I figure that there would be 6.4% loss over 1600 miles in a 1GW transmission system. That would then give 7.5 Watts loss per foot and also give a typical 6.4% loss. However, is 1600 miles a typical length in real world situations? Is 1GW a typical load?
    Last edited: Sep 17, 2013
  9. Sep 17, 2013 #8

    jim hardy

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    From that Wiki article:
    As your Wiki article mentions , losses are a lot less at high voltage.

    From that AEP article , page 4 :

    In between the power plant and the customer are switchyards, transformers and lots of lower voltage distribution lines. You can't ascribe all the 6% to the high voltage lines.
    So there's no "One number fits all" for transmission lines.

    And no, power plants are situated close to their intended loads. While the whole US is interconnected most power travels less than a few hundred miles from plant to consumer.
    Sixteen hundred miles is a LONG transmission line. A quarter wavelength at 60hz is what, 775 miles? When a line approaches that length it starts acting like an antenna. You don't want your power radiating off into space.
    Longest one I know of personally is the 500KV line that brings coal power from Southern Company's plants in Alabama and Georgia to South Florida. It's probably 350 miles. When you drive alongside it on US 27 you'll see every few miles two of the wires swap positions on the pole to reduce antenna effects. That's called transposing, it effectively makes them a twisted pair just like in audio work.

    1 GW sounds a lot for one line.
    The plant where I worked was ~2.2 gw, which is comparable to US side of Niagara Falls.
    Power left us on three lines and was mostly consumed within 250 miles.
    When long lines are highly loaded you start having problems from inertia effects - the rotating inertias at opposite ends can begin harmonic torsional oscillations between one another.

    So one GW isn't an inordinate load . But moving that much power over more than a very few hundred miles while not unheard of is not commonplace.

    I'm afraid that's the best answer I can offer. Maybe there's some genuine power guys on board.
    Last edited: Sep 17, 2013
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