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 the more closely they are placed the more magnetically coupled they become and hence becoming more efficient.
A transformer is a static piece of apparatus used for transferring power from one circuit to another at a
different voltage, but without a change in frequency. It can raise or lower the voltage with a corresponding
decrease or increase of current.
Losses 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 the primary and secondary winding, and there is a loss of electrical energy due to the resistance of the primary winding and secondary winding, and they are also called variable losses. These losses depend upon the loading conditions of the transformers. Therefore, these losses are also called variable losses.
Winding resistance is the result of current flowing through the windings causing 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’s current loss
2. Hysteresis loss
Eddy’s 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 the secondary winding, resulting in current flowing through the load connected with it. Some of the alternating flux of the transformer may also link with other conducting parts like the steel core or iron body of the transformer etc. As alternating flux links with these parts of the transformer, there would be an induced emf. Due to this emf, there would be current which will circulate at that parts of the transformer. These circulating currents will not contribute to the output of the transformer and dissipated heat. This type of energy loss is called the eddy current loss of the transformer.
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 the 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 the transformer is made of steel. Steel is a very good ferromagnetic material. These kinds of materials are very sensitive to being magnetized. That means whenever magnetic flux passes through, it will behave like a magnet. Ferromagnetic substances have a number of domains in their structure. Domains are very small regions in the material structure, where all the dipoles are paralleled in the same direction. In other words, the domains are like small permanent magnets situated randomly in the structure of the substance.
These domains are arranged inside the structure in such a random manner, that the net resultant magnetic field of the material is zero. Whenever an external magnetic field is applied to that substance, these randomly directed domains are arranged themselves in parallel to the axis of the applied magnetic field. After removing this external magnetic field, maximum numbers of domains again come to random positions, but a 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 the transformer. . According to Steinmetz’s formula, the heat energy due to hysteresis is given by,
Hysteresis loss is thus given by;
f = frequency
η= hysteresis coefficient
βmax= maximum flux density
Moreover, Hysteresis Loss depends on the 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
Variation of losses with loading level.
Variation in Constant losses.
Variation in Load Losses.
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