What is Transformer ??A transformer is a

static device which able to transfer the power from one circuit to another circuit without altering the frequency .

Principle Of Operation

Transformer works on the principle of mutual induction of two coils. When current in the primary coil is changed the flux linked to the secondary coil also changes. Consequently an EMF is induced in the secondary coil.

Primary and Secondary Windings

A two-winding transformer consists of two windings interlinked by a mutual magnetic field.– Primary winding – energized by connecting it to an

input source– Secondary winding – winding to which an electrical

load is connected and from which output energy is drawn.

Working…. When the primary winding is

connected to an ac supply mains, current flows through it. winding produces an alternating flux in the core. Since this flux is alternating and links with the secondary winding also, so induces an emf in the secondary winding. The frequency of induced emf in secondary winding is the same as that of the flux or that of the supply voltage. The induced emf in the secondary winding enables it to deliver current to an external load connected across it. Thus the energy is transformed from primary winding to the secondary winding by means of electro-magnetic induction without any change in frequency. 

Construction of Transformer

Mainly Transformers have two types of construction….

CORE type construction

SHELL type construction

Core type Transformer In the Core type

the primary and secondary windings are placed on each side of the core.

The core type has two limbs

Shell type Transformer In Shell type

transformers the LV and HV windings are sandwiched between each other.shell type has three limbs.

Ideal Transformers

No iron and copper lossesNo leakage fluxesA core of infinite magnetic

permeabilityFlux is confined to the core The windings have zero resistance

An ideal transformer is a lossless device with an input winding and an output winding. It has the following properties:

Equivalent Circuit of an Ideal Transformer at No Load

Types of TransformerStep UP Transformer : A transformer in which Ns>Np is called a

step up transformer. A step up transformer is a transformer which converts low alternate voltage to high alternate voltage.

Step DOWN Transformer : A transformer in which Np>Ns is called a

step down transformer. A step down transformer is a transformer which converts high alternate voltage to low alternate voltage.

A wide variety of transformer designs are used for different applications.

Auto-transformerPoly-phase transformerLeakage transformerResonant transformerInstrument transformers

AUTO-TRANSFORMERS

Autotransformer is a one winding transformer in which a part of the winding is common to both HV and LV sides.

POLY-PHASE TRANSFORMER• Three separate

single phase transformers are suitably connected for 3 phase operation.

• A single three phase transformer in which the cores and windings for all the three phases are combined in a single structure.

Losses In Transformers….

The losses that occur in transformers have to be accounted for in any accurate model of transformer behavior.

1. Copper (I2R) losses. Copper losses are the resistive heating losses in the primary and secondary windings of the transformer. They are proportional to the square of the current in the windings.

2. Eddy current losses. Eddy current losses are resistive heating losses in the core of the transformer. They are proportional to the square of the voltage applied to the transformer.

3. Hysteresis losses. Hysteresis losses are associated with the rearrangement of the magnetic domains in the core during each half-cycle. They are a complex, nonlinear function of the voltage applied to the transformer.

4. Leakage flux. The fluxes which escape the core and pass through only one of the transformer windings are leakage fluxes. These escaped fluxes produce a self-inductance in the primary and secondary coils, and the effects of this inductance must be accounted for.

Efficiency of a TransformerTransformer efficiency may be defined as the ratio between

Output and Input. Efficiency = Output/Input

• Efficiency = η= Output / Input• Efficiency = η= Output / (Output + Losses) …….… (As Input

= Output +Losses)• Efficiency = η= Output / (Output +Cupper Losses + Iron

Losses)

You may also find the Efficiency by the following formula• Efficiency = η = (Input – Losses) / Input …….… (As Output

= Input – Losses)Taking LCM• Efficiency = η = 1 – (Losses /Input)

What is Voltage Regulation ?

The voltage regulation is the change in terminal voltage of the secondary from no load to full load voltage.