Why is long range (very) high powered electric transmission best done with DC instead of AC?

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I was watching a YT video recently where they said something along the lines of “AC current is too inefficient for long distance power transmission, so xyz project needs DC power” and then moved on. I (from my vague memories 20 years ago of school) thought that AC had less loss and inefficiencies. What am I missing/what did I tune out in school?

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Anonymous 0 Comments

The most important thing for the efficiency of a transmission line is the voltage, because most of the losses are proportional to current, and higher voltage means you can transmit the same amount of power with less current.

AC is easier to step up to high voltage, but it has higher loss once it’s on the wire. DC only really cares about resistance, where AC is impacted by inductance and capacitance as well. AC also uses the conductors less efficiently due to skin effect, where DC uses more of the wire’s cross-section.

Basically, if you use AC, you’ve basically built a very low frequency radio transmitter, and that energy has to come from somewhere.

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