Transformer Basics And Fundamentals


A transformer is a static machine which transfers a.c electrical power from one circuit to another with out any electrical link between them. It essentially consists of two windings the primary and secondary, wound laminated magnetic core. The flux links both the windings and induces e m f according to the Farady’s Laws of Electromagnetic Induction.
Transformer Basics-stepdown transformer

Notes(Transformer Basics And Fundamentals)
  • The two windings of an isolation transformer are linked together by the magnetic filed.
    All values of a transformer are proportional to its turns ratio.
  • The ratio of the primary and secondary voltage determined by the ratio of the number of turns in the primary and secondary windings.
  • Step up Transformer:There are more turns on the secondary coil than the primary coil. The induced voltage across the secondary coil is greater than the applied voltage across the primary coil
  • Step down Transfoemer:A step down transformer has less turns on the secondary coil that the primary coil. The induced voltage across the secondary coil is less the applied voltage across the primary
Two types of connection

Wye and delta connection

  • Wye the phase voltage is less the line voltage by a factor of 1.732 .The phase current and line current are the same.
  • Delta connection :Te phase voltage is the same as in the line voltage the phase current less than line current by factor of 1.732.
  • Harmonics:Are the voltage or current that operate at frequencies that are multiples of the fundamental frequency usually 50 or 60.
  • Harmonics reduction :Reduce neutral current in three-phase systems by balancing currents in the phase legs. Reduce triplen harmonics on the neutral by adding filters.
  • There are two types of transformers Core type and shell type.

Transformer losses

Iron losses

This is the power loss that occurs in the iron part. This loss is due to the alternating frequency of the emf.
Transformer Basics -magnetic core loss

Iron losses =Hysteris loss+Eddy current loss=constant loss

Hysterisis loss:

This is the loss in the iron core, due to the magnetic reversal of the flux in the core, which results in the form of heat in the core. This loss is directly proportional to the supply frequency.The hysteresis loss can be minimised by using high silicon steel

Eddy current loss:

This power loss is due to the alternating flux linking the corewhich will induced an emf in the core called the eddy emf, due to which a current called the eddy current is being circulated in the core. As there is some resistance in the core with this eddy current circulation converts into heat called the eddy current power loss. Eddy current loss can be reduced by using core of thin lamination.

Copper losess

Copper loss occur in both these windings due to their ohmic resistnaces.Its also called variable resistance

Copper losess Pc=I1(R1)2+I2(R2)2

  • The rating of transformer is given in KVA .The total loss in the transformer depends upon Volt Ampere(VA)
  • Power Transformer used in generating stations having great efficiency.
  • Destribution transformers used for stepping down voltage and kept near consumer’s premises.
  • Current transformers for meashuring a.c current
  • Potential transformer for meashuring high voltage.
Theory of an ideal transformer

Transformer Basics-ideal transformer

  • No winding resistance.
  • No leakage flux.
  • No iron losses.
Short Circuit and Open Circuit Test(SC and OC)

Short Circuit test and Open circuit test used for determine the

    (i) equivalent circuit of transformer
    (ii) voltage regulation of transformer
    (iii) efficiency of transformer.

Open circuit (OC) test
open circuit test on transformer is used to determine core losses in transformer and parameters of shunt branch of the equivalent circuit of transformer.
Transformer Basics-Shorcircuit_Opencircuit_test

The shunt branch parameters can be determined by performing this test. Since, the core loss and the
magnetizing current depend on applied voltage, this test is performed by applying the rated voltage
to one of the windings keeping the other winding open (generally HV winding is kept open and rated
voltage is applied to LV winding).

Short Circuit Test on Transformer

Suppose the input voltage is reduced to a small fraction of rated
value and secondary terminals are short-circuited. A current will circulate in the secondary winding.
Since a small fraction of rated voltage is applied to the primary winding, the flux in the core and hence
the core loss is very small. Hence, the power input on short circuit is dissipated as heat in the winding.

Transformer Basics-Shorcircuit_Opencircuit_test


Effciency of the transformer ratio of output and input.

Efficiency of the transformer is defined as=Output power/(Output power+Iron losses+Copper Losses)



Hi, Myself Tony George. An Electrical Engineer by Education, a Software Developer by Profession and an Education Blogger by Passion. In the past, I had been working as an Engineer in KSEB. The knowledge that I have acquired I would like to share here with you. I will be happy if these articles can give you a way to your career growth. Feel free to contact me.

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6 Responses

  1. jeena says:

    nice notes

  2. sreelekshmi says:

    Hi Tony,
    Can you please send me notes for some of the important topics to be covered for preparing for kerala PSC Assistant professor Electrical Engineering.Thanking you in advance.

  3. SUJITH says:


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