Question:Why is high voltage electricity more efficient than high current electricity in the national grid?
In electrical wires, electric current causes heating, and the higher the current the greater the heating.
If high current electricity was used in the national grid, then most of the electrical energy would be converted to heat before it could reach our homes and the wires would have to be much thicker to prevent their simply melting, which would make hanging the wires from pylons much less practical etc..
So electrical energy is transmitted at high voltage to reduce energy waste and costs. At the high voltages used there is still a loss of around 20% just in the wires.
So, due to Joule Heating at any given power transmission, an increased voltage reduces current, so decreasing energy waste by reducing heating of cables.