AC/DC have different costs for voltage converters and per-distance efficiency, so there are some distances where AC makes more sense and others where DC makes more sense; the distance changes as tech improves.
AC mostly conducts on the outer surface of the wire, while DC conducts with the whole cross section, giving you different scaling issues as the current changes.
Under water, AC suffers from significant capacitive loss — the wire acts as one side of a capacitor and the entire ocean as the other.
At certain frequencies and wire lengths you also get inductive losses, though IIRC that affects only RF cables in practice and and the design of the trans-Siberian railway in theory as no other place even seriously considered having a sufficiently long conductor for the frequency used.
AC/DC have different costs for voltage converters and per-distance efficiency, so there are some distances where AC makes more sense and others where DC makes more sense; the distance changes as tech improves.
AC mostly conducts on the outer surface of the wire, while DC conducts with the whole cross section, giving you different scaling issues as the current changes.
Under water, AC suffers from significant capacitive loss — the wire acts as one side of a capacitor and the entire ocean as the other.
At certain frequencies and wire lengths you also get inductive losses, though IIRC that affects only RF cables in practice and and the design of the trans-Siberian railway in theory as no other place even seriously considered having a sufficiently long conductor for the frequency used.