# . Explain the Schematic Design of Transformer

A schematic diagram for a transformer is shown here. The transformer consists of a rectangular soft iron core made up of laminated sheets, well insulated from one another with two sets of coils on either side, the primary and the secondary. The soft-iron core causes the two sets of coils to be magnetically linked (i.e. there is ‘coupling’and hence mutual inductance) such that when an alternating current is passed through the Primary coil it induces a magnetic flux in the secondary.

Let the input voltage supplied by AC source E=E0+sin(wt)

Now, this creates an induced emf  Ep across the primary coil due to EMI. Similarly, an induced emf  Es appears across the secondary. If  Np  is the number of turns in the primary and Ns  in the secondary coils, then,

Es/Ep=Ns/Np

The term  Ns/Np=k  is called the transformation ratio and depending on it’s value (i.e. >1 or <1) the transformer has a step-up or a step-down function. In a step-up transformer, the primary coil is made of a few turns of copper wire whereas the secondary coil consists of large number of turns of copper wire. In a step-down transformer, the primary coil consists of large number of turns of insulated copper wire whereas the secondary coil consists of few turns of fine insulated copper wire.