How could I determine the resistance of electric transmission lines?
I face a lot of problems in determining the resistance of electric transmission lines, for example:
"if we need to deliver an amount of power from a power station to a factory to be used there, and the distance between them is 1000km, and we would use transmission lines, and the resistance per km is 0.25Ω.......etc."
When I start to solve the problem and try to determine the whole resistance of the transmission lines, I do this:
R(tot.)= 0.25*1000 = 250Ω.
But what I find is that this step is wrong, and the total resistance will be determined as this:
R(tot.)= 2*0.25*1000 = 500Ω.
That is what I find in my text book, and that confused me, and I would like if someone helped me and explains this. Are there always two lines to connect power stations and the consumers, because I find that "2" used in the equation, in every solution to a problem like the one above?