Tap to Read ➤

How Does a Transformer Work?

Aarti R Oct 23, 2018
Transformers are basically used to change AC (Alternating Current) voltage and transfer electricity from one part of a circuit to another. They have a primary winding and a secondary winding around a core.
A transformer is a device that converts alternating current (AC) from the specified level to the desired one. It is used to increase or decrease AC voltage. A transformer is made up of a soft iron and windings on the primary and secondary side.
The core is made of material like air, soft-iron and steel. It transfers electricity from the primary winding to the secondary winding. These windings are wound on the iron core, but they are never connected to each other.
The part of the winding that receives the input alternating voltage is known as the 'primary' side, while the side from where the desired voltage level is drawn is known as the 'secondary' side.

Working of a Transformer

The working of a transformer is based on the relationship between magnetism and electricity. When the alternating current is supplied to the primary, the current creates a magnetic field in the primary region.
This changing magnetic field, by the Law of Induction, induces alternating current at the secondary side. The voltage that is received at the secondary side depends upon the number of turns of the secondary coil.
This equation gives the relation between the number of turns of the coils and the voltage.
The primary coil and the secondary coil are inductively coupled to each other. Usually, an iron core is used, because it provides high permeability to the magnetic flux. Magnetic flux is the amount of magnetic field passing through a given area. Permeability is a property of iron that allows the magnetic flux to flow through the core.
Higher the permeability, less is the resistance offered to the magnetic flux that is flowing through the core. In case of iron core, most of the magnetic flux is restricted only to the core. Due to this restricted magnetic flux, there is a higher degree of coupling between the primary and the secondary coil.
For the construction of the primary and secondary coils, specific value gauge wires are used. As the input/primary side is not subjected to very high voltages, smaller-value gauge wires are used, while for the output/secondary side, gauge wires with higher values are considered.
The voltage that is received at the secondary can be 'stepped-up' or 'stepped-down' depending upon the number of turns of the coils. If the voltage requirement at the output is higher than the input voltage, then a 'step-up' transformer is used.
However, if the voltage requirement at the output is lower than the input voltage, then a 'step-down' transformer is used. Now we'll have a look at the construction and working of these devices.

Step-Up Transformer

As the name suggests, induced voltage is stepped-up from the primary one. The number of turns of the secondary coil is greater than the number of turns at the primary side. Thus, secondary voltage is higher than the primary one.
For example, if the number of primary turns are 10 and the secondary turns are 100, then the secondary voltage will be 10 times higher than the primary one. Step-up transformers are used in power distribution systems for long distances.

Step-Down Transformer

Step-down transformers lower the input voltage to a desired one. The input voltage that is fed to the primary coil produces an alternating magnetic field. This field induces an alternating current at the secondary side.
As the number of turns of the secondary coil is less than that on the primary side, the voltage that is induced is also less. For example, if the number of turns on the primary side is 100 and the secondary side is 10, the output voltage will be 1/10th times lower than the input one.

Ideal Transformer

Ideal transformers are the ones that have no losses at all. The input and the output impedance is zero, thus the entire voltage fed at the coils is received at the output. It is considered to be 99% efficient. There is no leakage flux or eddy current losses in the transformer.
This is the equation for an ideal transformer.
Secondary voltage is proportional to the primary voltage, and it is equal to the ratio of the number of turns of the secondary coil to the primary coil. If the load is connected to the transformer, the secondary to primary voltage ratio will be equal to the primary to secondary current ratio, as there is no impedance.
All transformers do not have only one coil at the output. A single primary winding and a single voltage source can be used to obtain voltages of different values at the output. This is done by using separate windings for the secondary, according to the required output voltage. This makes it easy to provide the required voltage by utilizing a single source.
In modern-day power systems, transformers are adjunct devices. They are used for electricity distribution over long distances. The electricity transmitted from the power generation stations is of very high voltage, so that it can travel long distances.
Current and potential transformers are used in the power generation and distribution sectors. Transformers also find their use in audio amplifiers and radio receivers.