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A transformer is a static device which is use to convert high alternatic voltage to a low alternatic voltage and vice versa, keeping the frequency same.
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.
What is Induction law ?
Faraday’s law states that:
Vs=Ns.dΦ/dt
where VS is the instantaneous secondry winding voltage.
NS is the number of turns in the secondary coil.
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 & HV windings are sandwiched between each other.shell type has three limbs.
Types of Transformer
Step UP Transformer :
A transformer in which Ns>Np is called a step up transformer. A step up transformer is a transformer which converts low alternatic voltage to high alternatic 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 alternatic voltage to low alternatic voltage.
A wide variety of transformer designs are used for different applications.
Auto-transformer
Poly-phase transormer
Leakage transformer
Resonant transformer
Instrument transformers
AUTO-TRANSFORMERS
Autotransformer is a one winding transformer in which a part of the winding is common to both HV & 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.
INSTRUMENT TRANSFORMERS
A current transformer is a measurement device designed to provide a current in its secondary coil proportional to the current flowing in its primary.
A voltage transformer are designed to have an accurately known transformation ratio in both magnitude and phase, over a range of measuring circuit impedances..