A power transformer is a device used to convert electrical energy from one AC voltage level to another. It is one of the most common components of an electrical power system, used to step up or step down the voltage of the electrical current as needed. It consists of one or more coils of insulated wire wrapped around an iron core, allowing the core to be magnetically charged to alter the current in the secondary coil when the primary coil is charged. Transformers are an efficient means of transferring energy between two circuits, resulting in minimal losses. The transformer must be designed to match the load characteristics; wrong design can result in increased losses, instability, and possible destruction of the transformer.