How a transformer works

A transformer is an electrical device that is used to convert AC power at a certain voltage level to AC power at a different voltage, without changing the frequency.

A transformer is constructed using a ferromagnetic core around which multiple coils, or windings, of copper wire are wound. The winding which is connected to the electrical source or the input is called the ‘primary’ coil, while the load or the output winding is the ‘secondary’.

When an alternating current is passed through a copper wire, a magnetic field is generated around the wire. If a second wire is brought within this magnetic field, a corresponding alternating current is created within the second wire. In technical terms a current is ‘induced’ in the second wire.

The alternating current in the primary coil induces an alternating magnetic flux (f) that flows around the ferromagnetic core, changing direction during each electrical cycle. The alternating flux in the core in turn induces an alternating current in each of the secondary coils. The voltage induced in each of the secondary coils is directly related to the primary voltage by the turns ratio (N), the number of turns in the primary coil divided by the number of turns in the secondary coil. The voltage transformation ratio (primary voltage to secondary voltage) and the current transformation ratio (primary current to secondary current) depend on the turn’s ratio. Thus, the voltage can be easily changed lower or higher by selecting the correct number of turns. A transformer may have multiple secondary coils to feed a number of electrical loads.

Figure 1:
Basic Transformer

Figure 2:
Transformer core with magnetic flux


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