Why Transfer Power At High Voltage

A friend once ask me why is it that the power transmission is always being done with high voltage, well, the reason is due to power transmission efficiency. As an example, supposed that we need to transfer 1 kilo Watt across some miles away, and the total cable resistance involves is 1Ohm, the efficiency calculation will be:

And plotting the graph shows that efficiency suffers as the voltage decreases.

As usual, more details are available in Wikipedia:

http://en.wikipedia.org/wiki/Electric_power_transmission

read through and have fun J