How do Transformers work?

A Transformer is a stationed device used for transforming electrical energy from one a.c circuit to another. It changes voltages from low to high or high to low without changing the frequency. A Transformer changing voltage from low to high voltage is called a Step-up Transformer whereas the one changing voltage from high to low voltage is called a Step-down Transformer.

figure 1. Step down Transformer

In order for a transformer to do its work it must follow a certain working principle and this is Faraday's law of electromagnetic induction. It states that the magnitude of the induced Electromotive force in a circuit is directly proportional to the rate of change of magnetic flux linked with the circuit.

The construction of a Transformer

A Transformer is made up of an iron core on which wires are wound to form Primary coil (P) and Secondary coil (S) as shown in figure 1 above. The primary coil is connected to the source of a.c supply and the secondary coil is connected to the load.
The iron core constitutes a number of laminations of soft iron but sometimes silicon steel is used instead to reduce Hysteresis loss.

figure 2. Transformer laminations

The laminations are insulated from each other with paper or vanish in order to minimize the eddy currents.

A current carrying conductor produces a magnetic field around it, and when this conductor is placed near a ferromagnetic material (like the transformer core) it induces a magnetic flux within the material. You might be asking yourself, 'why are ferromagnets chosen to be the core?' I think it's because they pose low reluctance to the flow of magnetic flux.

figure 3. Current carrying conductor

When the primary coil draws alternating current from its source, an alternating magnetic flux is induced in the iron core, see figure 1 above.

Whenever current changes direction, in the primary coil, the induced magnetic flux also changes direction (alternates) and whenever this happens the secondary coil cuts the magnetic flux and produces the voltage different from the supplied voltage.
Since the magnetic flux is alternating, the current which the secondary coil produces also alternates. This is mutual induction.

A transformer is housed in a metallic box to protect it from dust and sometimes the box is designed with fins on it for cooling purpose.

Distribution transformer

Transformers are used; in transmission system to step up voltage from 6.6 KV to 33 KV or 132 KV, in distribution system to step down voltage from 11 KV or 6.6 KV to 440 volts or 240 volts and in electronics.Transformers enable the transmission of electricity at high voltage with low current.

In electronics transformers step down voltage from 240 volts to other lower voltages.The picture below shows a switched mode power supply transformer.

Types of Transformers
There are two types of transformers namely:
1. Auto Transformer
2. Double wound Transformer

An Auto Transformer has its winding common to both Primary and Secondary circuit.

Auto transformer are usually used for starting induction motors and discharge lamps. But the one in the picture is used to step down voltage for a radio receiver.














The double wound transformer is the one I have been explaining earlier in this post.