How is current lowered as Voltage is increased in AC power transmission
120The idea is that a different load is used with the different voltages. As a simple example:


on 120V: a 120V/120W lightbulb is 120 ohms (when hot) and draws 1 amp.
on 240V: a 240V/120w lightbulb is 480 ohms (when hot) and draws 1/2 amp.


In both cases, the load is 120 watts but by doubling the voltage, we get away with 1/2 the current, allowing smaller wires.

Similarly, we could start out with the 240V 1/2A, put that into a 2:1 transformer, and get out 120V 1A for the 120V lightbulb. For the 240V section of the transmission, we can reduce the wire size due to the lower current. Now scale this up to 10KV transmission lines going into 120V/240V residental wiring.