A step-down transformer is an electrical device whose primary voltage is greater than its secondary voltage. Transformers transfer energy between circuits using electromagnetic induction. Using varying magnetic fields, transformers are designed to efficiently change voltage levels within power networks.
Transformers are critical for distributing and using electrical energy by increasing voltage before transmitting energy through wires over long distances. Transformers also allow power plants to be located remotely from where power is used. Most of the world's electrical power passes through a series of transformers before reaching the end user. Transformers also decrease voltage as needed for end users. For example, they are used to isolate individual homes from full supply voltage. Transformers typically last for 20 to 25 years because they have no moving parts that can break.
A wide range of transformer sizes and designs is used in electric power applications. Huge transformers connect directly to the power grid and weigh hundreds of tons. They are made with two or more coils of insulated wire, which is wound around an iron core. Voltage is applied to the primary coil, which magnetizes the iron core. The core creates voltage in the other coil, known as the secondary or output coil. The number of turns in the wire as it is wound determines the available voltage of the transformer.