Friday, 17 October 2014

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A transformer is a static piece of apparatus by mean of which electric power in on e circuit is transformed into electric power of the same frequency in another circuit .it can raise or lower the voltage in a circuit but with a corresponding decrease or increase in current. the physical basis of a transformer is mutual induction between two circuit linked by a common magnetic flux .in its simplest form it consist of two inductive coils which are electrically separated but magnetically linked through a path of low reluctance .the two coils posses high mutual inductance. If one coil is connected to a source of alternating voltage ,an alternating flux is setup in the laminated core, most of which is linked with the other c oil in which it produces mutual inducted emf according to faraday’s laws of electromagnetic induction E =MdI/dt .If the second coil circuit is closed ,a current t flows in it and so electric energy is transferred from the first coil to the second coil. The first coil in which electric energy is fed from the ac supply mains called primary winding and other from which energy is drawn out is called secondary winding

The rate of change of flux linkage depends upon the amount of linked flux, with the second winding. So it desired to be linked almost all flux of primary winding, to the secondary winding. This is effectively and efficiently done by placing one low reluctance path common to both the winding. This low reluctance path is core of transformer, through which maximum number of flux produced by the primary is passed through and linked with the secondary winding. This is most basic   theory of transformer .

constructional parts of transformer

  • Primary Winding of transformer - which produces magnetic flux when it is connected to electrical source

  • Magnetic Core of transformer - the magnetic flux produced by the primary winding, will pass through this low reluctance path linked with secondary winding and creates a closed magnetic circuit

  • Secondary Winding of transformer - the flux, produced by primary winding, passes through the core, will link with the secondary winding. This winding is also wound on the same core and gives the desired output of the transformer


  • The  transformer  which increases the   a.c. voltage   is called   step up   transformer .

  • The  transformer  which decreases  the   a.c. voltage   is called   step down transformer .

E s is the voltage generated in the secondary coil.

E p  is the voltage given to primary coil.

N s  is the number of the turns in the secondary coil.

N p  is the number of the turns in the primary coil. 

where   K  is called as transformation ratio.

  • If K>1 then the transformer as step up transformer.

  • if K<1 then the transformer as  step down transformer.

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