How Transformers Work

A transformer is embarrassingly simple: two coils of wire wrapped around an iron core. AC flowing through the first coil (primary) creates a changing magnetic field. That field induces a voltage in the second coil (secondary).

Want to step 230V up to 400,000V for transmission? Wind the secondary coil with roughly 1,740 times more turns than the primary. At the other end, reverse the ratio to step it back down. Transformers are over 99 percent efficient — almost no energy lost.