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It is said that AC is preferred over DC because of the negligible voltage drop over long distances. How does that work?

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closed as unclear what you're asking by Bill N, Aaron Stevens, Martin Beckett, user191954, John Rennie Oct 28 '18 at 6:04

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    $\begingroup$ The title is asking why low voltage drops are desirable while the question statement is asking how AC avoids voltage drop problems. Which did you want to ask about? $\endgroup$ – Nat Oct 28 '18 at 2:43
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    $\begingroup$ "It is said...." Who said that? The voltage drop is not negligible. It's just less than it would be if user level voltage was in the transmission line. Your question is not clear. $\endgroup$ – Bill N Oct 28 '18 at 2:50
  • $\begingroup$ Basically my question was how voltage drop is desirable in context of AC and DC. $\endgroup$ – Shanza Oct 28 '18 at 4:49
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    $\begingroup$ Possible duplicate of Why high voltage transmission lines? $\endgroup$ – Martin Beckett Oct 28 '18 at 4:57
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    $\begingroup$ Possible duplicate of Why do we use AC for long distance transmission? $\endgroup$ – John Rennie Oct 28 '18 at 6:04
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The voltage drop in long-distance transmission lines is mostly caused by 1) resistance losses in the wires and 2) capacitive coupling between the wires and the ground underneath them. AC versus DC does not matter to resistive losses in the wires (same in either case) but the capacitive coupling to the ground happens with the AC transmission and gets progressively worse as the transmission voltage is raised.

Since higher transmission voltages mean lower resistive losses in the wires, the tendency is to go for higher voltages and that means the AC-specific losses become dominant. For this reason, very high voltage power transmission experiments are being done on lines carrying DC. Note however that AC transmission lends itself to easy conversion of high to lower voltages with transformers, which cannot be used with DC lines.

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  • $\begingroup$ Wikipedia has some good articles on High-voltage direct current, but it doesn't have much info on the latest UHVDC projects. $\endgroup$ – PM 2Ring Oct 28 '18 at 10:08

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