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Originally Posted by oil pan 4
Brazil currently has the longest DC transmission line. Something like 600 to 700 miles with almost no line loss.
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Not true. The Pacific DC Intertie is about 850 miles, from Celilo near Bonneville Dam on the Columbia River, to the Sylmar converter station in the LA Basin. There are even longer ones - 1200-1400 miles - in other countries.
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You are correct, there should be no need to move power that distance, but when a (failed) government refuses to build power plants within a very large state, voilą stupidity prevails and demand is created for that which defies logic.
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Sorry, but you're wrong here. There's a very good economic case for long-distance transmission, as for instance with the above DC intertie. You have dams (and now wind farms) on the Columbia producing a lot of cheap hydroelectric power, with relatively low local demand in the summer, when Southern California power demand is highest. So it makes perfect sense to ship the excess power south in the summer, and perhaps ship SoCal's excess north in the winter.
Other long-distance HVDC lines are used where you have hydroelectric generation located a long way from where the demand is, as for instance near the shore of Hudson Bay.
There are also some very good technical reasons to have large power grids, and to interconnect grids with DC. It has to do with powerflow & stability issues. Everything on an AC grid has to run at essentially the same frequency & phase; individual lines can carry only so much power without overheating; power can't really be stored, but must be used as it produced; and individual power plants & lines can fail for all sorts of reasons, and sometimes need to be taken off-line for maintenance.