A transformer is a device by which the voltage of an input alternating supply may be changed. The frequency of the supply, however, remains unchanged.
- 2 coils of wire (not connected to each other) known as the primary and secondary windings, are electrically insulated from each other and wound on a laminated soft iron core.
- The number of primary Np and secondary Ns turns may be varied for attaining the desired electrical power at the load.
- The iron core is to confine the magnetic field lines to ensure macimum magnetic flux linkage between the primary and secondary coils. (flux density $\uparrow$ $\rightarrow$ flux linkage $\uparrow$ $\rightarrow$ induced emf $\uparrow$) This is due to the fact that iron is easily magnetised, hence the iron core guides and direct the magnetic field lines.
An ideal transformer has the following additional features:
- Resistance of primary and secondary coils rp and rs are zero, so that no energy is lost in the core or in the coils.
- It is 100% efficient = input power equals output power
- No magnetic flux losses, hence both coils have the same flux through them.
Note: Transformers are assumed to be ideal in all calculations. However, we have to keep in mind thart the features of the ideal transformer are only assumed.