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Transformer | What Is Transformer | Types Of Transformer

Transformer | What Is Transformer | Types Of Transformer :- A transformer is a static electrical device that, through electromagnetic induction, transfers electrical energy at a constant frequency from one AC circuit to one or more other AC circuits, for the purpose of increasing the voltage level (step-up transformer) or decreasing it (step-down transformer).

Principle Of Transformer

(Transformer | What Is Transformer | Types Of Transformer)

A transformer operates on the principle of mutual induction.

Construction

The main components of a transformer are as follows :-

(i) Primary Coil : It is an electrically insulated copper coil that is connected to the input alternating voltage source. When an electric current flows through it, it produces a magnetic field.

(ii) Secondary Coil : It is also an electrically insulated copper coil from which the output alternating voltage is obtained. It receives energy from the magnetic field produced by the primary coil.

(iii) Core : The core is made by stacking rectangular sheets of soft iron one over the other. An insulating material is applied between these sheets. The primary coil is wound around one limb of the core, and the secondary coil is wound around the other limb. The core provides an easy path for the magnetic flux produced by the primary coil so that the maximum flux can reach the secondary coil. The core is laminated to prevent the formation of eddy currents.

Types Of Transformers

(Transformer | What Is Transformer | Types Of Transformer)

On the basis of voltage control, these are of two types :

(i) Step up transformer : If the number of turns in the secondary coil is greater than the number of turns in the primary coil, i.e., N_S > N_P, then it is called a step-up transformer.

(ii) Step down transformer : If the number of turns in the secondary coil is less than the number of turns in the primary coil, i.e., N_S < N_P, then it is called a step-down transformer.

Working Of Transformer

(Transformer | What Is Transformer | Types Of Transformer)

The alternating current applied to the primary coil produces an alternating magnetic flux in the core. This alternating magnetic flux induces an alternating emf in the secondary coil according to the principle of electromagnetic induction. The induced voltage in the secondary coil depends on the ratio of the number of turns in the primary and secondary coils.

Assuming an ideal transformer, if the leakage of flux is considered zero, then the rate of change of flux in the primary and secondary windings will be equal.

$\displaystyle {{\left[ \frac{d\phi }{dt} \right]}_{P}}={{\left[ \frac{d\phi }{dt} \right]}_{S}}$ …..(1)

The electromotive force induced in the primary coil (or the applied alternating voltage),

$\displaystyle {{E}_{P}}=-{{N}_{P}}{{\left[ \frac{d\phi }{dt} \right]}_{P}}$ …..(2)

Similarly, the induced electromotive force in the secondary coil,

$\displaystyle {{E}_{S}}=-{{N}_{S}}{{\left[ \frac{d\phi }{dt} \right]}_{S}}$ …..(3)

From equations (2) and (3),

$\displaystyle \frac{{{E}_{S}}}{{{E}_{P}}}=\frac{-{{N}_{S}}{{\left[ \frac{d\phi }{dt} \right]}_{S}}}{-{{N}_{P}}{{\left[ \frac{d\phi }{dt} \right]}_{P}}}$

$\displaystyle \frac{{{E}_{S}}}{{{E}_{P}}}=\frac{{{N}_{S}}}{{{N}_{P}}}$

$\displaystyle \therefore {{E}_{S}}=\left( \frac{{{N}_{S}}}{{{N}_{P}}} \right){{E}_{P}}$ …..(4)

In equation (4), if N_S > N_P, it is called a step-up transformer because the output voltage is higher than the input voltage. Conversely, if N_S < N_P, it is called a step-down transformer because the output voltage is lower than the input voltage.

The ratio $\displaystyle K=\left( \frac{{{N}_{S}}}{{{N}_{P}}} \right)$ is called the turns ratio or transformation ratio.

If the energy loss in the transformer is considered negligible, then

Power supplied to the primary coil by the source = Power delivered by the primary coil to the secondary coil

$\displaystyle {{E}_{P}}{{I}_{P}}={{E}_{S}}{{I}_{S}}$ …..(5)

Current flowing in the secondary coil,

$\displaystyle {{I}_{S}}=\left( \frac{{{E}_{P}}}{{{E}_{S}}} \right){{I}_{P}}=\left( \frac{{{N}_{P}}}{{{N}_{S}}} \right){{I}_{P}}=\frac{{{I}_{P}}}{K}$ …..(6)

For a step-up transformer, K > 1, ⇒ I_S < I_P, i.e., the current decreases in the same proportion as the voltage increases. Similarly, for a step-down transformer, K < 1, ⇒ I_S > I_P.

From equation (6),

$\displaystyle {{I}_{P}}=\left( \frac{{{N}_{S}}}{{{N}_{P}}} \right){{I}_{S}}=\left( \frac{{{N}_{S}}}{{{N}_{P}}} \right)\times \frac{{{E}_{S}}}{R}=\left( \frac{{{N}_{S}}}{{{N}_{P}}} \right)\times \frac{1}{R}\times \left( \frac{{{N}_{S}}}{{{N}_{P}}} \right){{E}_{P}}$

$\displaystyle \therefore {{I}_{P}}=\frac{1}{R}{{\left( \frac{{{N}_{S}}}{{{N}_{P}}} \right)}^{2}}{{E}_{P}}=\frac{{{E}_{P}}}{{{R}_{eq}}}$ …..(7)

In equation (7), $\displaystyle {{R}_{eq}}={{\left( \frac{{{N}_{P}}}{{{N}_{S}}} \right)}^{2}}R$ is the resistance of the load as seen from the source. This can be visualized as if the source of voltage E_P is connected through a resistance R_eq, resulting in a current I_P flowing in the circuit.

Efficiency Of Transformer (η)

(Transformer | What Is Transformer | Types Of Transformer)

The efficiency of a transformer is defined as the ratio of output power to input power.

$\displaystyle \eta =\frac{Output\text{ }Power}{Input\text{ }Power}=\frac{{{E}_{S}}{{I}_{S}}}{{{E}_{P}}{{I}_{P}}}$ …..(8)

To express the efficiency in percentage, it is multiplied by 100.

The efficiency of an ideal transformer is 100% (η = 1), but in a real transformer, due to various types of energy losses, the efficiency is less than 1 (i.e., less than 100%).

Energy Loss In A Transformer

(Transformer | What Is Transformer | Types Of Transformer)

(1) Core Losses (Iron Losses) : There are two types of energy losses in the core :-

(a) Hysteresis Loss : The alternating magnetic flux repeatedly magnetizes and demagnetizes the core, generating heat. This heat loss is minimized by using a material with low hysteresis (soft iron) in the core.

(b) Eddy Current : The alternating magnetic flux induces eddy currents in the core, causing it to heat up. This effect is minimized by using a laminated core.

(2) Flux Leakage : Due to imperfect core design or the presence of air gaps, the total magnetic flux produced by the primary coil cannot be entirely transferred to the secondary coil; some flux is inevitably lost. To reduce this loss, both coils are tightly wound on a coaxial soft iron core with high magnetic permeability, thereby maximizing the coupling coefficient (K → 1).

(3) Resistance of coils : Due to the heating effect of electric current (I²Rt), energy is lost in copper coils. To reduce this loss, high-current coils are made with thick wires, and mineral oil circulation is used to remove the heat generated.

Previous Topic :- Wattless Current | What Is Wattless Current

Complete List of Topics :-

Transformer | What Is Transformer | Types Of Transformer

Principle Of Transformer

(Transformer | What Is Transformer | Types Of Transformer)

Types Of Transformers

(Transformer | What Is Transformer | Types Of Transformer)

Working Of Transformer

(Transformer | What Is Transformer | Types Of Transformer)

Efficiency Of Transformer (η)

(Transformer | What Is Transformer | Types Of Transformer)

Energy Loss In A Transformer

(Transformer | What Is Transformer | Types Of Transformer)

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