Hydropower - AC or DC

Another huge advantage of using HVDC for power transmission is that there are no stability issues. For instance, since the province of Quebec uses HVDC connections to the outside world, it was not affected by the massive blackout of 2003. But don’t take my word for it…

“Because HVDC allows power transmission between unsynchronised AC distribution systems, it can help increase system stability, by preventing cascading failures from propagating from one part of a wider power transmission grid to another, whilst still allowing power to be imported or exported in the event of smaller failures. This has caused many power system operators to contemplate wider use of HVDC technology for its stability benefits alone.”
-source: http://en.wikipedia.org/wiki/High-voltage_direct_current
That doesn’t mean we would want to generate DC though.

The issue of Scientific American currently on the news stands has an article about an improved powergrid design which uses HVDC.