The 1200 mile Xiangjiaba–Shanghai HVDC line in China has transmission losses "well under 7%" [1]. This line was also completed almost three years ahead of schedule, which is an excellent contrast to Western nuclear plants that are being constructed in China. But then, nobody knows how to complete the AP1000 or EPR on time or on budget, as far as I can tell.
Lots of HVDC lines are going to be essential for cheap power in the US in the future, I just hope the political will materializes for that.
[1] http://3phasepower.blogspot.com/2010/08/xiangjiaba-shanghai-...
Edit: corrected the nuclear comparison.
Sure, on one hand, this kind of project is likely to get into cost overruns. On the other hand, Areva looks like a fairly dysfunctional company following the tenure of Anne Lauvergeon, so it's not only a technical problem.
http://www.postandcourier.com/news/newly-released-report-hig...
Such behavior seems to be borderline criminal, particularly covering up the internal audit.
Yet this is par for the course on nuclear these days.
Even worse, maintenance and running costs of superconducting cables are likely much higher due to the cooling (high temperature superconductors are "high temperature" in comparison to other superconductors - there's still lots of cooling needed).
Transmission is a solved problem, as far as regional power is concerned.
Not really. You'd have to do periodic helicopter patrols of the lines themselves. There isn't really that much "maintenance" that occurs on the line, definitely on the xfmrs/rectifiers/inverters though, but that is normal for any transmission/substation owner.
Also, expected losses are ~5%