The transformer — Recall

Use P = I^2R to explain why power losses in cables are smaller when the transmission voltage is greater.

The power dissipated as heat in a cable is given by P = I^2R. To transmit a given amount of power, using a higher voltage means a smaller current is needed (since power = current x voltage). Because the power loss depends on the square of the current, this smaller current produces a much smaller power loss in the cable's resistance.