Transformer: definition and working principle

Transformer: definition and working principle

A transformer is a static device and used to transfer the alternating power from one electric circuit to another electric circuit. The process of transferring power is done without any rotating part. In  construction of the transformer, all parts are static. That’s why this device is known as a static device.

The alternating power has a frequency. When power transfers from one circuit to another circuit, the frequency of the alternating power is not changing. Why frequency is not changing? Let get an answer form principle.

transformer working principle

We can see that, there are two electrical circuits (winding) and one magnetic circuit. Both electrical circuits are not connected physically. But these circuits connected by one common magnetic circuit. By this magnetic circuit, the transformer is capable to transfer the power. The transformer works on the principle of electromagnetic induction. This phenomenon says that if we apply the alternating current across the coil then alternating flux induces in the coil. The magnitude of the flux is directly proportional to the current induces in the coil and the direction of flux is depends on the direction of the current. By the right-hand rule, we can determine the direction of flux.

When a source of alternating voltage (V1) apply to the electric circuit and an alternating current flow. This alternating current produces an alternating flux in the magnetic circuit. The frequency of this alternating flux is same as the supply frequency and that will never change. This alternating flux links with another electrical circuit with that same frequency. I hope you got your answer, still, if you have a problem, you can comment your problem and I’ll try to solve.

Principle of transformer

Now, this flux induces EMF in the coil. This induced EMF cause because of the alternating current. According to the Lenz’ law, the causes always oppose the effect. Here, the effect is the EMF and this induced EMF opposes the supply voltage. Means, the polarity of induces EMF is opposite to the supply voltage.

transformer working principle

Let us consider that, the second coil place near the alternating flux of the first coil. So, according to the Faraday law of electromagnetic induction, the EMF is induced in the second coil. Because of the induced EMF, a small amount of current produce in the second coil. The magnitude of the current depends on the reluctance of the magnetic path. As shown in above figure, If the air use as a medium, the reluctance of air is much higher. So, a very small amount of current will flow. But, in the case of a transformer, we use core with low reluctance material like steel. Hence, entire flux produce in the first coil is link with the second coil and equal magnitude of current will flow through the second coil.

Working of transformer

The transformer has two main parts; core and winding. The core made from the laminated silicon steel. This provides the low reluctance path to the magnetic flux.

In the transformer, we have two winding; primary winding and secondary winding. The winding through which we supply input, that winding is known as the primary winding. The winding through which we connect the load, that winding is known as the secondary winding.

When we give the alternating supply to the primary winding, an alternating current will start flowing through the primary winding. Because of this current, the flux induces in the winding. According to the self-induction phenomena, the EMF induced in the primary winding. As discussed in the principle, the induced EMF is opposite polarity of the supply voltage (according to the Lenz’ law).

Because of the mutual-induction phenomena, the flux induce in the primary winding link with the secondary winding. The EMF is induced in the secondary winding. The current is following through the secondary winding because of this EMF. The magnitude of the secondary current is almost the same as the primary current. This happens because we uses a low reluctance path. In this case, almost all flux induced in the primary links with the secondary winding.

The ratio of primary to secondary turns (T1/T2), which equals the ratio of primary to secondary induced voltage (E1/E2). This ratio is nothing but the transformation ratio and it is denoted by ‘a’.

a = E1/E2 = T1/T2

Hence, by selecting turns ratio, you can achieve input and output voltage.

Step-up and Step-down Transformers

The output voltage (secondary voltage) is greater than its input voltage (primary voltage). This transformers are step-up transformers. The output voltage (secondary voltage) is lower than its input voltage (primary voltage). This transformers are step-down transformers.

The same transformer can use as a step-up and step-down transformer. When the transformer use as a step-up transformer, the low voltage winding is primary. When the transformer use as a step-down transformer, the high voltage winding is primary.

If turns ratio is the same, means both winding have the same number of turns. In this condition, the transformer uses to isolate two circuits.

Related Article:

Transformer: Construction and Classification

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