Speaking on Deep Background, the Press Secretary whispered:
Maybe a stupid question...
But what if the huge distribution systems used DC and the whole thing
was only converted to AC close to the users in small installations?
This would get rid of the frequency problems.
True, and it's done. There are two very large DC lines in use:
The Pacific Intertie, from Washington State down to Califunny
A line from the Great Frozen North down to Minnesota.
There's also a short tie between 2 grids; I think it strattles
the Mississippi but I don't recall for sure.
DC has multiple advantages, but they don't shine through until
the line gets large and long. There are fixed losses in the
AC->DC and DC->AC conversions you need to make up for.
Plus, it's only in the last decade or so that we've had the power
semiconductor technology to do the conversions well. But we've
been doing AC lines for eons, so there's considerable inertia.