I actually thought transmission of DC was more efficient than AC, because you don't have inductive losses (hence HVDC underground cables etc) but that the issue is more the ease of AC transmission, since building transformers is easy but converting from AC to HVDC and back was difficult before the advent of switching converters.
Correct. HVDC is significantly more efficient than AC transmission. The problem before modern power semiconductors was always that converting voltages levels was difficult. The Pacific DC Intertie had to use huge Mercury Vapor Rectifier TUBES.
> Even for a frequency as low as 60 Hz the skin depth is less than the 1.6" radius of the conductor used for the Intertie. Hence the effective resistance is greater with AC than DC, so that more power is lost to heat. A DC line is also ideal for connecting together two AC systems that are not synchronized with each other. Also, cascading blackouts are less likely.
Interesting point that this was the longest HVDC transmission in the world until the Three Gorges Dam projects.
