## Friday, November 21, 2008

A transformer is a device that transfers an alternating current from one electric circuit to another by means of electromagnetic induction, transforming voltage from one level to another, usually from a higher voltage to a lower voltage. A changing current in the first circuit, the primary, creates a changing magnetic field. This changing magnetic field induces a changing voltage in the second circuit, the secondary. This effect is called mutual induction.

A transformer is made up of two or more coils of insulated wire wound around a core made of iron. The number of times the wires are wrapped around the core ("turns") is very important and determines how the transformer changes the voltage.

If a load is connected to the secondary circuit, electric charge will flow in the secondary winding of the transformer and transfer energy from the primary circuit to the load connected in the secondary circuit. The secondary induced voltage VS, of an ideal transformer, is scaled from the primary VP by a factor equal to the ratio of the number of turns of wire in their respective windings: Vs/Vp=Ns/Np.

Electrical transformers can be wound to have either a single-phase or a three-phase configuration. Transformers come in a range of sizes from a thumbnail-sized coupling transformer hidden inside a stage microphone to huge units weighing hundreds of tons used to interconnect portions of national power grids. All operate with the same basic principles, although the range of designs is wide.

The transformer principle was demonstrated in 1831 by Michael Faraday, although he used it only to demonstrate the principle of electromagnetic induction and did not foresee its practical uses. The first widely used transformer was the induction coil, invented by Irish clergyman Nicholas Callan in 1836. He was one of the first to understand the principle that the more turns a transformer winding has, the larger electromotive force it produces.