Transformer is a static (or Stationay ) electrical device which can
Transfer the electrical power from one circuit to another .
Does this with increasing or decreasing of voltage by
decreasing or increasing of current .
Does this without change in frequency.
Accomplish this by ELECTROMAGNETIC INDUCTION. .
What is Transformer ???
Transformer is not an energy
conversion device, but it is
device that changes AC
electrical power at one
voltage level into AC
electrical power at another
voltage level through the
action of magnetic field but
with a proportional increase
or decrease in the current
ratings., without a change in
Classification Of Transformers :
In the terms of Numbers of Phases
1. Single PhaseTransformer
2. Three PhaseTransformer
Depending on the voltage level at which the winding is operated
Depending upon Construction of transformers
1. SHELL type
2. CORE type
• SHELL Type Transformer
Core sorrounded the
considerable part of winding .
•CORE Type Transformer
Winding sorrounded the
considerable part of core .
The transformer consists of soft iron core or the silicon steel core
and two inductive windings attached to it i.e. primary winding and the secondary
winding such that core and the windings are insulated from one another.To prevent
insulation lamination is done on the core to provide low reluctance path for the
The winding provided to the AC source is known as primary winding
and winding across which load is taken out is known as secondary winding.
Principle of operation :-
The Principle of Operation of transformer is
based Upon Faraday’s Laws of Electromagnetic Induction which
Principle of Operation
Transformer works on the
Induction of two coils , i.e.
“When Current Flowing
Through a coil changes ,
an induced e.m.f. is
produced in the
neighboring coil “.
When the primary winding is connected to AC mains
supply, a current flows through it. Since the winding links with the
core, current flowing through the winding will produce an
alternating flux in the core.The changing magnetic flux links with
the secondary & according to Faraday’s law of electromagnetic
induction induces an e.m.f. in it. EMF is induced in the secondary
coil since the alternating flux links the two windings.Thus power is
transferred from primary coil to secondary coil .The frequency of
the induced EMF is the same as that of the flux or the supplied
It convert a low voltage at high current into a high voltage
at low current . In this type of transformer , numbers of turns of
secondary coil is more than that in primary , i.e. , Ns>Np . here
primary coil is made up of a thick insulated copper wire & Sec. coil is
made of thin insulated copper wire .
It converts a high voltage
at low current into a low voltage at high current . In this type of
transformer , numbers of turns in secondary coil is less than that in
primary ,i.e., Ns<Np . Here primary coil is made of thin insulated
copper wire & secondary coil is made of thick insulated copper
Power transmission :
A major application of transformers is to
increase voltage before transmiting electrical energy over long
distances through wires. Wires have resistance and so dissipate
electrical energy at a rate proportional to the square of the
current through the wire. By transforming electrical power to a
high-voltage (and therefore low-current) form for transmission
and back again afterward, transformers enable
economical transmission of power over long distances .
Transformers can rise or lower the level of Voltage or
It can increase or decrease the value of capacitor , an
inductor or resistance in an AC circuit.
It can be used to prevent DC from passing from one
circuit to the other.
It can isolate two circuits electrically.
Other Applications …
•Losses in Transformers
Although a transformer is a very efficient machine
as there are no moving parts in it , yet it suffers from a numbers of losses
Copper losses inTransformer(I²R)
Iron losses (Eddy Current losses)
An ideal transformer is an imaginary transformer
which does not have any loss in it, means no core losses, copper losses and
any other losses in transformer. Efficiency of this transformer is considered
The resistance of the primary and secondary winding are negligible.
Self-inductance of the winding & mutual inductance between them are
very large .
There are no energy losses with it so that its efficiency is 100%
There is no any leakage of magnetic flux.
Coefficient of coupling is K=1.
Transformer must not be connected to a direct source.
If the primary winding of a transformer is connected
to a DC supply mains, the flux produced will not vary but remain
constant in magnitude and therefore no e.m.f. will be induced in
the secondary winding except at the moment of switching on.
Thus the transformer can not be employed for raising or lowering
the dc voltage. Also there will be no back induced e.m.f. in the
primary winding and therefore a heavy current will be drawn from
the supply mains which may result in the burning out of the
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