Transformer

Definition

A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils.

A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core, and thus a varying magnetic field through the secondary winding.

This varying magnetic field inducesa varying electromotive force (EMF)or voltage in the secondary winding. This effect is called mutual induction.

The phenomenon of electromagnetic induction was discovered independently by Michael Faradayand Joseph Henryin 1831. However, Faraday was the first to publish the results of his experiments and thus receive credit for the discovery.

Faraday's experiments including winding a pair of coils around an iron ring, thus creating the first toroidal closed-core transformer.

The first type of transformer to see wide use was the induction coil, invented by Rev. Nicholas Callan of Maynooth College, Ireland in 1836. He was one of the first researchers to realize that the more turns the secondary winding has in relation to the primary winding, the larger the increase in EMF.

The Ideal Transformer

A lossless device with an input winding and an output winding.

The transformer has Np turns of wire on its primary side and Ns turns of wire on its secondary sides. The relationship between the primary and secondary voltage is as follows:

The relationship between primary and secondary current is: Np ip (t) = Ns is (t)

Note that since both type of relations gives a constant ratio, hence the transformer only changes value of the magnitude of current and voltage. Phase angles are not affected.