In this YouTube video (scrolled to 5:55) there's a claim that replacing an AC high voltage transmission line with a high voltage DC transmission line allows for having seven times fewer powerlines (the video shows how seven lines evaporate, then one line appears and the cutting in the forest gets narrower).
How is that possible? I've read the Wikipedia article and it claims that
The power delivered in an AC system is defined by the root mean square (RMS) of an AC voltage, but RMS is only about 71% of the peak voltage. The peak voltage of AC determines the actual insulation thickness and conductor spacing.
but that doesn't explain seven times less power lines.
How is such massive (seven times) saving possible when switching from AC to DC transmission?
Best Answer
A significant factor, and probably the major one here, is the increase in voltage. They are comparing apples with pears and then some.
Power = Vrms x Irms.
BUT resistive line losses are proportional to I^2.
So if you increase voltage by a factor of "N" then current for the same power drops by a factor of N and losses drop as N^2, as
Losses at I are proportional to I^2
Losses at I/N are proportional to (I/N)^2 = I^2 / N^2.
Their original AC lines are 500 kV.
Their DC line is 800 kV.
N = 800/500 = 1.6
N^2 = 1.6^2 = 2.56 .
To get to 7 x you need a factor of 7/2.56 = 2.7
For the same number of wires you will need 2.7 x the area or about 1.65 x the diameter. And/or lower resistance material. Maybe more copper and less aluminum.
Then there is a loss of capacitive losses from AC.
A significant factor is that ABB have been around a long long time and 'know their stuff'. It won't be magic - just applied engineering - and the claim will be true as presented - but there will still be some smoke and mirrors. How BIG is that new tower? How visible are the wires ... ?. The fact they are doing it means thy believe they can make more money and save the customer money or equivalent in the process.