How does an electric transformer work?

The grey box on your street's pole has no moving parts, yet it turns 11,000 volts into the 230 volts in your socket. A transformer is two coils of wire wound on a core of thin steel sheets. Every turn on the core feels the same volts, so V₂ ÷ V₁ = N₂ ÷ N₁.

Read how it works: How does an electric transformer work? · The history of the transformer · More boxes on Glassbox

Chapters in this interactive model

1. Inside the transformer on your street: A steel tank of oil with an iron core and two sets of copper coils. No moving parts.
2. Changing flux, induced voltage: AC in one coil makes a changing flux in the core, and that flux makes a voltage in the other coil.
3. From power station to phone: Up to 400,000 volts to cross the country, then down, step by step, to 5 volts for your phone.
4. Where the lost energy goes: Core loss is there all day. Copper loss grows with the load squared. Oil and fins carry the heat away.
5. Three phases, delta and star: Three voltages, a third of a cycle apart. 400 V between phases, 230 V from any phase to neutral.
6. Summer overloads, fires and the Buchholz relay: Heat ages the insulation. A small relay listens for gas. And you should never go near one.