A transformer converts a high voltage of alternating current power to a lower voltage while keeping it on the same frequency. High-voltage electricity is able to travel longer distances with less energy wasted, but homes and businesses use a lower voltage, so the electricity needs to be converted with transformers.

When electricity moves through metal wires, the electrons move around rapidly and escape through the metal structure, causing energy waste. The higher the voltage used, the lower the current, so power companies send out extremely high voltage to conserve as much energy as possible. High-voltage power lines can carry 155,000 to 765,000 volts. Once the high-voltage energy is converted, the new, lower voltage is stored at a power substation, which then breaks it down into smaller pieces at even lower voltage.

Using smaller transformers, the substations repeat the process until the voltage reaches about 7,200, and the lower-voltage power then travels out from the substation to neighborhood transformers. The energy is then converted again to the lower voltage used by consumers, which is typically 110 to 250 volts. Smaller transformers are found at the ends of most chargers for MP3 players, cell phones and laptops, because those things typically require a very small amount of energy.