Principle of Transformer

  • The transformer is a static device which transfers electrical power from one side to other side without change of frequency. 
  • One or more winding of transformer are linked with common magnetic circuit. 
  • The winding connected to alternating supply side is called as primary winding whereas the winding connected to load side is called as secondary winding
Step up Transformer & Step down Transformer
  • When the output voltage is greater than the input voltage, the transformer is called as step up transformer. 
  • Similarly when the output voltage is less than the input voltage, it is called as step down transformer.  


Mutual Induction
  • The transformer works on the principle of mutual induction. 
  • Let us consider that there are two winding which close to each other. one winding ( A ) is acts as primary winding whereas the second winding ( B ) acts as secondary winding.  
  • When an alternating supply is given to primary winding of the transformer, current I1 passes through that winding. 
  • The flux Ф produces in the primary winding due to current I1
  • As this flux links with secondary winding, an alternating emf produces in the secondary winding according to Faraday’s law of electromagnetic induction. 
  • The amount of emf in the secondary winding depends upon what amount of flux links with the secondary winding.

        e = M ( dI / dt )
       Where e = Induced emf
                M = Mutual inductance
            di/dt = Rate of change of current

Self induced emf & Mutual Induced emf 
  • The induced emf in the primary winding is called as self induced emf whereas the induced emf in the secondary winding is called as mutual inducted emf.


What is happened when DC is given to the transformer primary winding?
  • When the DC is applied to the transformer primary winding, the flux produces in the core remain constant in magnitude therefore no induced emf in the primary winding as well as secondary winding. 
  • As the back emf of the primary winding is zero and resistance of the winding quite low, heavy current flows through the winding result in the burning of the primary winding.
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