> The efficiency of high voltage AC power lines is limited by capacitive coupling to ground.
And to this point, HVDC has been slowly rising as a viable alternative beyond just undersea transmission.
A mistaken belief is that AC is more efficient than DC. What AC is is more easy to transform from one voltage to another (until somewhat recently). That makes it easier to run AC at 1 MV and then step it down to 240V for residential applications.
The cost is as AC voltage goes up, capacitive resistance increases. This is part of the reason why high voltage lines have such huge towers with the lines far apart.
An HVDC line, however, can be put underground (or water) without suffering power losses. It's voltage can go well above that of AC voltages with the only limit being how much insulation we need for the line.
Super conductors are nice, but only in the "now we can run 1 billion amps at 100V" sense to avoid the capactive resistance. Without any sort of special materials you get most of the benefits of super conductors by using HVDC. The only real downside is high voltage DC is still super dangerous. Cut the insulation and you've got something that can arc meters whereas a superconductor at lower voltages would be about the same danger as any other conductor at lower voltages.
Minor nitpick — "now we can run 1 billion amps at 100V" — there is a limit to how much current you can put down a superconductor. For example I think commercial YBCO superconductor tape will do roughly 1000A/mm^2 (and even that requires being significantly below its critical temperature).
That’s a pretty high current density compared to what’s feasible with copper — don’t get me wrong — but a billion amps would still require a pretty huge cable even with a superconductor.
Presumably everything in the chain, every junction, would also need to be a pure super conductor? Anything else would be susceptible to instantly melting or vaporising.
So unless someone comes up with super conducting welding I guess that would mean no junctions.
"A mistaken belief is that AC is more efficient than DC. What AC is is more easy to transform from one voltage to another (until somewhat recently). That makes it easier to run AC at 1 MV and then step it down to 240V for residential applications."
DC is also used because a conductor can carry more current per kg than AC due to not having any skin loss. You can use smaller wires, less metal, less dollars.
And to this point, HVDC has been slowly rising as a viable alternative beyond just undersea transmission.
A mistaken belief is that AC is more efficient than DC. What AC is is more easy to transform from one voltage to another (until somewhat recently). That makes it easier to run AC at 1 MV and then step it down to 240V for residential applications.
The cost is as AC voltage goes up, capacitive resistance increases. This is part of the reason why high voltage lines have such huge towers with the lines far apart.
An HVDC line, however, can be put underground (or water) without suffering power losses. It's voltage can go well above that of AC voltages with the only limit being how much insulation we need for the line.
Super conductors are nice, but only in the "now we can run 1 billion amps at 100V" sense to avoid the capactive resistance. Without any sort of special materials you get most of the benefits of super conductors by using HVDC. The only real downside is high voltage DC is still super dangerous. Cut the insulation and you've got something that can arc meters whereas a superconductor at lower voltages would be about the same danger as any other conductor at lower voltages.