Power loss is a function of current. So major transmission lines use very high voltage to lower the current (and thus the power loss). Of course, there are lo

Power loss is a function of current. So major transmission lines use very high voltage to lower the current (and thus the power loss). Of course, there are losses at the transformer(s) the step the voltage up and down. Unsurprisingly, it's a very use-case-dependent engineering problem.