Download Losses occur in Transformer

LOSSES OCCUR IN TRANSFORMER
LOSS
MUHAMMAD
ARBAB - 134
 SYED MUHAMMAD SAMI

UDDIN - 139

MUHAMMAD FAISAL - 133
GROUP # 12
Transformer
A transformer is a device with two inductors sharing a common
magnetic path, any two inductors placed
reasonably close to each other will work as a
transformer and more closely they are place
the more magnetically coupled they become
and hence becoming more efficient.
OR
A transformer is a static piece of apparatus
used for transferring power from one circuit
to another at a
different voltage, but without change in frequency. It can raise or
lower the voltage with a corresponding
decrease or increase of current.
Losses occur in Transformer
Transformer losses are produced by the electrical current flowing in
the coils and the magnetic field alternating in the core.
Basically two types:
1. Copper losses
2. Iron losses or core losses
Copper Loss :
When the transformer is loaded,
current flows in primary and secondary
winding, there is loss of electrical
energy due to the resistance of the
primary winding, and secondary
winding and they are also called
variable losses. These losses depends
upon the loading conditions of the
transformers. Therefore, these losses are also called as variable
losses.
Winding resistance is the result of current flowing through the
windings cause resistive heating of the conductors.
Overcome: Copper Losses or Heat Losses can be removed by
using suitably thick wire.
Iron losses/core losses :
The losses that occur in the core are known as core losses or
iron losses. The two types of iron losses are:
1. Eddy current loss
2. Hysteresis loss
Eddy current loss :
When we supply alternating current in the primary, this
alternating current produces alternating magnetizing flux in the
core and this flux links with secondary winding there will be
induced voltage in secondary winding, resulting current to flow
through the load connected with it. Some of the alternating flux of
transformer may also link with other conducting parts like steel
core or iron body of
transformer etc. As
alternating flux links with
these parts of
transformer, there would
be an induced emf. Due to
these emf there would be
current which will
circulate at that parts of
the transformer. These circulating current will not contribute in
output of the transformer and dissipated as heat. This type of
energy loss is called eddy current loss of transformer.
More …..
The alternating flux induces an e.m.f in the bulk of the core
proportional to flux density and frequency.
The resulting circulating current depends inversely upon the
resistivity of the material and directly
upon the thickness of the core. The losses per unit mass of core
material, thus vary with square of
the flux density, frequency and thickness of the core laminations.
By using a laminated core(thin sheets of silicon steel instead of a
solid core) the path of the eddy
current is broken up without increasing the reluctance of the
magnetic circuit.
Overcome: Eddy currents can be avoided by making
the core
laminated, made of thin sheets of soft iron. Each sheet is separated
from the next by a layer of insulating varnish.
Hysteresis loss :
The magnetic core of transformer is made steel. Steel is very
good ferromagnetic material. These kinds of materials are very
sensitive to be magnetized. That means whenever magnetic
flux passes through, it will behave like magnet. Ferromagnetic
substances have numbers of domains in their structure.
Domains are very small region in the material structure, where
all the dipoles are paralleled to same direction. In other words,
the domains are like small permanent magnet situated
randomly in the structure of substance. These domains are
arranged inside the structure in such a random manner, that
net resultant magnetic field of the material is zero. Whenever
external magnetic field is applied to that substance, these
randomly directed domains are arranged themselves in parallel
to the axis of applied magnetic field. After removing this
external magnetic field, maximum numbers of domains again
come to random positions, but some few of them still remain in
their changed position. Because of these unchanged domains
the substance becomes slightly magnetized permanently. This
magnetism is called "Spontaneous Magnetism". To neutralize
this magnetism some opposite magnetic field is required to be
applied. The magnetic field applied in the transformer core is
alternating. For every cycle, due to this domain reversal there
will be extra work done. For this reason, there will be a
consumption of electrical energy which is known as Hysteresis
loss of transformer. . According to Steinmetz's formula, the
heat energy due to hysteresis is given by;
, and,
Hysteresis loss is thus given by;
Where,
f = frequency
η= hysteresis coefficient
βmax= maximum flux density
Moreover, Hysteresis Loss depends on applied voltage and its
frequency
Overcome:
Hysteresis loss can be avoided by using special alloys
known as "Perm Alloy" for the core material.
Some Other Losses :
Stray Loss or Flux Leakage:
Some loss of useful energy occurs because a small
amount of the flux associated with the primary coil fails to pass
through the secondary. So Flux Leakage
is by itself a small loss, since energy
supplied to its magnetic field is returned
to the supply with the next half-cycle.
However, any leakage flux that
intercepts nearby conductive material
such as the transformers support
structure will give rise to eddy current
and be converted to heat. There are
also radiative losses due to the
oscillating magnetic field but these are usually small.
Dielectric Loss :
It is roughly proportional to
developed high voltage and the type and thickness of insulation. It
varies with frequency. It is
negligibly small and is roughly constant.
Variation of losses during operation :
The losses vary during the operation of a transformer due to
loading, voltage changes, harmonics and
operating temperature.
Variation of losses with loading level.
Variation in Constant losses.
Variation in Load Losses.
Etc . . . .
END