# Features Of An AC Transformer

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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.

Physical Features:

• 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.