Types of Losses in Transformer Explained

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 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.

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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

          β_max=  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