Purpose of transformer:
Transformer as the name itself implies that which transfers power from one circuit to another circuit without changing frequency.
The power transfer is in two ways
1.It transfers power as it is without any modification of input voltage and currents. This is called Isolating transformer .
2.It transfers power by changing the voltage or current level from input to output side. This is used as step up or step down transformer to match the two different voltage or current circuits.
All these are made possible by using different number of turns on primary and secondary sides of transformer.
The ratio of number of turns on secondary side to the number of turns on primary side is called transformation ratio.
This ratio is equal to one means on both sides of the transformer the number of turns are same, then it is called isolating transformer.