What is Transformer?
A transformer is a static electrical device that transfers energy
by inductive coupling between its winding circuits. A varying current in
the primarywinding creates a varying magnetic flux in the
transformer's core and thus a varying magnetic flux through
the secondary winding. This varying magnetic flux induces a
varying electromotive force (emf) or voltage in the secondary winding.
Transformers range in size from thumbnail-sized used in microphones to
units weighing hundreds of tons interconnecting the power grid. A wide
range of transformer designs are used in electronic and electric power
applications. Transformers are essential for
the transmission, distribution, and utilization of electrical energy.
The ideal transformer:
Consider the ideal, lossless, perfectly-coupled transformer shown in the
circuit diagram at right having primary and secondary windings with
NP and NS turns, respectively.
2. The ideal transformer induces secondary voltage ES =VS as a proportion
of the primary voltage VP = EP and respective winding turns as given by
- VP/VS = EP/ES = a
is the voltage ratio and NP/NS = a is the winding turns ratio, the
value of these ratios being respectively higher and lower than unity
for step-down and step-up transformers,
- VP designates source impressed voltage,
- VS designates output voltage, and,
- EP & ES designate respective emf induced voltages.
Any load impedance connected to the ideal transformer's secondary
winding causes current to flow without losses from primary to secondary
circuits, the resulting input and output apparent power therefore being
equal as given by the equation
Combining the two equations yields the following ideal transformer
This formula is a reasonable approximation for the typical commercial
transformer, with voltage ratio and winding turns ratio both being
inversely proportional to the corresponding current ratio.
The load impedance is defined in terms of secondary circuit voltage
and current as follows
The apparent impedance of this secondary circuit load referred to the
primary winding circuit is governed by a squared turn’s ratio
multiplication factor relationship derived as follows:
APPLICATION OF TRANSFORMER:
The most important uses and application of a
It can rise or lower the level of level of voltage or current
(when voltage increases, current decreases and vice versa
because P=V*I, and power is same ) in an AC circuit.
It can increase or decrease the value of capacitor, an
inductor or resistance in an AC circuit. It can thus act as an
impendence transferring device.
It can used to prevent DC from passing from one circuit to thr
It can isolate two circuit electrically.
Transformer is the main reason to transmit and distribute power in
AC instead of DC, because Transformer not work on DC
so there are too difficulties to transmit power in DC 9in the DC
transition and distribution the level of voltage step up by buck and
boost converter but it is too costly and not suitable economically.
In other word, increase or decrease the level of current, while
power must be same other used and application of transformer.
It step up the level of voltage at generation side before
transmission and distribution in distribution side for commercial or
domestic use of electricity, transformer step down (decrease) the
level of voltage for example from 11kV to 220V single phase and
440 v three phase.
4. The current transformer and potential transformer also used power
system and in the industry also it is used for impendence
Pole mount distribution transformer with centre tapped secondary
winding used to provide split phase power for residential and light
commercial service, which in Pakistan is typically rate 120/220 volt
source if image and attribution.
Losses on Transformer:
In a transformer there are different types of energy losses. The input
power slightly differs from the output power. Transformers are made of
soft iron core and insulated copper wires. They both have several
electrical properties which causes power loss in a transformer. How
Energy loss Occurs:
Current flowing through the windings causes resistive heating of
the conductors. At higher frequencies, skin effect and proximity
effect create additional winding resistance and losses.
We know that magnetic flux is the fundamental thing behind the
working of a transformer. All the flux linked with the primary coil
may not cut the secondary coil. Thus energy losses in the form of
leaked flux. We have to think how to reduce the energy loss due to
flux leakage? It can be done by minimizing the flux leakage. That’s
why in some efficient transformers, primary coil and secondary coil
5. winds one over the other. Thus almost all the flux produced by the
primary coil will cut the secondary coil.
Everyconductors, even super conductors have certain amount of
resistance. A transformer uses copper wires, which causes some
energy loss as heat. H=I^2RT.
Eddy current losses:
when conductors are subjected to change in magnetic flux,
induced currents are produced in them like circular loops termed
as eddy current. The alternating magnetic flux induces eddy
current in the transformer core. Due to the resistance offered by
the iron core heat energy will create. This is the principle used in
an induction cooker. Thus a large heat will generate at the core of
the transformer. Eddy current losses can be lowered by using
some energy is losses as heat during the magnetizing and
demagnetising process of the core.
In addition to magnetostriction, the alternating magnetic field
causes fluctuating electromagnetic forces between the primary and
secondary windings. These incite vibrations within nearby
metalwork, adding to the buzzing noise, and consuming a small
amount of power.