[rohan alhat]

rohan alhat asked the Naked Scientists:
   
Is it true that direct current (DC) electricity is not able to travel as far as AC (alternating current)?

What do you think?

[Vern]

No, it is not true. AC current is used because transformers can increase the voltage while reducing the current. The reduced current allows for more efficient conduction over wires. Then when the reduced current arrives in the user's area, it is transformed back down to less voltage and more current.

DC will do the same if you can somehow transform the voltage and current.

[syhprum]

All really long transmission links today are DC, this has that advantage of lower cable losses with the possibility of using superconductive cable.
It also has the advantage of being able to connect regions of different AC generation without the need for synchronisation (the AC supply at the source is converted to DC and then reconverted to AC at the load).
There is a small degree of storage due to the capacitance of the cable that makes for greater stability in the system.
Links have been proposed between Iceland, Scotland and Germany to make use of abundant geothermal power. 

[chris]

The undersea cables must be DC otherwise the energy will all be dissipated moving ions backwards and forwards underwater!

In the first tests of undersea power transmission people were rather surprised to see apparently very high resistances - unless DC was used. As this does not produce a changing magnetic - and hence electrical - field, it does not cause charged dissolved species to move, hence the losses are lower.

Chris