Learn the basics of Electrical Engineering.

Basics of Transformers

A transformer is a magnetically coupled device which contains two windings. The magnetic field produced by the time-varying current in one winding induces a voltage in the other winding.

In this post, you'll learn
  1. Parts of transformer
  2. Working principle of transformer
  3. Symbol of transformer
  4. Types of transformer
  5. Examples

What is it made of?

All types of transformers essentially contain three components:
  1. The core: It is the metallic part which is made up of a special type of steel.
  2. Primary winding: Coils of wire to which input is applied
  3. Secondary winding: Coils of wire from which we take the input.
Two possible arrangements for these parts are:

Rectangular core type

The primary and secondary windings are wrapped on any of the two opposite sides of the rectangular core.

Shell type core

The core is made up to a three-legged structure. The primary and secondary windings are wrapped around the central leg.

Working principle of a Transformer

A transformer works on Faraday's law which states that a time changing magnetic field is equal to the rate at which flux linking to the circuit is changing.

The number of turns plays the fundamental role in stepping voltages.
The relationship between turns ratio and voltages are:

Where Np/Ns is the turns ratio and is expressed as a
A transformer having two turns on primary and 10 turns on secondary will step up the 4 V to 20 V or 8 V to 40 V. Such transformer is known as step-up transformers.

On the other hand, a transformer with 20 turns on primary and 5 turns on secondary will step down the 10 V to 2.5 V. Such a transformer is known as the step-down transformer.

Symbol of transformer

Let's take a look at iron, ferrite and air cores tran.
As the name show, the iron core has a core made of iron and so on. Most of the times iron and ferrite are lumped together. Yet ferrite is an oxide of iron and is not pure iron.

Types of transformers

Transformers are of many types since this post is about basics only the names of types are presented here: You can read the theory of types here.


Statement: A transformer has a turn ratio of 0.2. Where Np = 200 and Ns = 1000. Is it step up or step down, and what will be the output if we provide an input of 300 volts.

Solution: The number of turns on primary are 200 and on secondary 1000 so it is a step up transformer. Also whenever turns ratio is less than 1. (Here 0.2) it is step up. Now for input of 300 volts.
Np / Ns = Vp / Vs
200/1000 = 300/Vs
pr Vs = 300 * 1000 / 200
Vs = 1500.
The transformer will provide an output of 1500 volts.

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