TRANSFORMER        

   ELECTRICAL CIRCUIT  DIAGRAM OF  TRANSFORMER 

 

TRANSFORMER WORKING:

Transformer is a static device in which the emf will be induced due to mutual induction principle .This principle is also applicable to the induction motor.

The Single phase transformers primary winding is applied with 230v AC supply and frequency of 50HZ . The emf will be induced in primary winding according to the Faraday's Laws of Electro Magnetic Induction. The induced emf is proportional to the rate of change of magnetic flux with respect to the change in time. when dc supply is applied to the transformer there is no change in the magnetic field with respect to time. So there is No emf induced.

So dc supply is not applied to transformer. The emf induced by applying AC supply is

                           E  = -N d(flux)/dt

When the proportionality is removed the constant N is replaced.

The "-" sign indicates that the emf induced is opposite to the applied voltage according to the Lenz Law. The Lenz Law defines that "oppose the  cause to it".

This induced emf is called as back emf accross the primary winding. By applying kvl in the primary side of electrical circuit of transformer we get

                       V  -  E  - IZ   =   0 -----------(1)

From above we can write for current as

                             I  =   (V - E)/Z  ---------(2)

And we know that when current flows in a coil produces flux (basic law) . So by flowing of current "I" in primary winding the flux is induced in primary winding.

This flux passes through the core of transformer to the secondary winding of transformer. So we know that where there is a change in flux with respect to time emf will be induced.

So that emf will be induced in secondary winding same according to Faraday's Laws of Electro Magnetic Induction.

Some losses takes place in secondary winding due to its impedance and the final terminal voltage is given by

                           By applying kvl in secondary circuit of transformer we get

                        E  -  IZ  -  V  =  0

                         E  =  V  +  IZ  --------- (3)

From above equation we can write for terminal voltage:
       
                         V  =  E  -  IZ  -----------(4)

This is the final terminal voltage of transformer when input voltage is applied.

When the terminals are open circuited then there is small amount of current flows through the terminals.

        i.e,        I  =  (E - V)/Z -------- (5)

On open circuit the impedance will be almost infinity
                   Z  = infinity
             
              I  =  (E - V)/Z  =   0 ---------(6)

The current through the secondary terminal depends on the type of laod. Which will be seen in another post.