# Transformer Working Principle

**Transformer – Introduction:**

The main advantage of AC over DC is that, the alternating current can be easily transferable from low voltage to high or high voltage to low voltage.

Alternating voltages can be raised or lowered as per requirements in the different stages of electrical network as generation, transmission, distribution and utilization.

This is possible with the help of static device known as Transformer.

**What is transformer?**

The transformer is a static piece of electrical apparatus by means of which an electrical power is transformed from one alternating current circuit into another circuit with the desired change in voltage and current, without any change in the frequency.

**Transformer Working Principle:**

- A transformer is a static device.
- It transforms electric power in one circuit into another circuit with the same frequency.
- It will raise or lower the voltage in a circuit with a corresponding decrease or increase in circuit.
- Remember that the frequency can not be changed.
- The fundamental concept of the electrical transformer is
*mutual induction*between two circuits linked by a common magnetic flux. - The simple transformer (shown in the above figure) consists of two inductive coils which are electrically separated but magnetically coupled through a path of low reluctance.
- The two coils consists of high mutual inductance. The coils are named as primary and secondary coils.
- The coil which is connected to the source is called as primary coil and the coil which is connected to the load is known as secondary coil.
- When the primary coil is connected to a AC source, an alternating flux is set up in the transformer core.
- Most of them are linked with the other coil in which it produces mutually induced emf as per the
*Faraday’s law of Electromagnetic Induction*. - If the secondary coil is closed, a current flows in it and thus electric energy is transferred from the first coil to the secondary coil.

**Transformer Operation:**

**At No Load:**

- When an AC voltage (V1) is applied to the primary winding and the secondary winding is not connected to any load (open circuit condition) a small amount of current flows in the primary.
- It is called as the no load current(I
_{O}). This sets up a magnetic flux in the core. - This alternating flux links with both primary and secondary windings.
- It induces the EMF of E1(in primary winding) and E2(in secondary winding) by means of mutual induction.

The induced e.m.f. E in a coil given by

**E = −N(dΦ/dt)**volts,

where

N – No of turns

dΦ/dt – The rate of change of flux.

For ideal transformer, the dΦ/dt is same for both primary and secondary coils.

So

**E1/N1 = E2/N2**

i.e. the induced EMF per turn is constant.

By considering no losses,

E1 =V1 and E2 =V2

Therefore

**V1/N1 = V2/N2**

or

**V1/V2 = N1/N2**

Voltage ratio = Turns ratio

This called as transformation ratio of the transformer.

If N2 < N1 then V2 < V1 and the device is called as step down transformer.

If N2 > N1 then V2 > V1 and the device is called as step up transformer.

**With load condition:**

- When a load is connected across the secondary winding, a current I
_{2}flows. - As the losses are neglected in an ideal transformer, it is considered as 100% efficient.

Hence

Input Power= Output Power

or

**V1.I1 =V2.I2**

i.e. The primary and secondary ampere-turns are equal

Thus

**V1/V2 = I2/I1**

Combining both the equations

**V1/V2 = N1/N2 = I2/I1**

**The summary is**

The transformer

- transfers electric power from one circuit to another
- will raise/lower the voltage/current in the secondary circuit
- cannot change the frequency
- works in electromagnetic induction principle

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