How do transformers reduce energy loss in long-distance alternating-current power lines?

Transformers reduce energy loss in long-distance power lines by enabling the transmission of electric power at very high voltages.

When electricity travels through transmission lines, it encounters electrical resistance, which causes energy to be lost as heat—a phenomenon known as Joule heating. The power lost ($P$) is calculated by the formula:

$$P=I^{2}R$$

In this equation, $I$ represents the current and $R$ represents the resistance of the wire. Because the power loss is proportional to the square of the current, even small reductions in current significantly decrease energy waste.1

Transformers are used at generating stations to "step up" the voltage. Since power is the product of voltage and current, increasing the voltage allows the same amount of power to be transmitted using a much lower current. By minimizing the current, transformers effectively limit the energy dissipated as heat during long-distance transmission. At the destination, other transformers "step down" the voltage to levels safe for consumer use.21