The principal advantage of sending electric power across country on very high voltage transmission lines is that it minimizes the power loss due to resistance in conductors.
To answer this question, we must keep in mind the relationship between power, current and resistance, that can be written as:
[tex]P=I^2R[/tex]
So power is dissipated as heat. From the equation, the power loss in the transmission line is proportional to [tex]I^2[/tex]. Another relationship we need to talk about is between power, current and voltage:
[tex]P=VI[/tex]
As you can see, current is inversely proportional to voltage, so if you increase the voltage, then the current decrease and the power loss also decreases.
