Transformer

Transformer

VP  :  V= NP :  NS

  • VP   voltage across the primary coil in V
  • VS    voltage induced in the secondary coil in V
  • NP    amount of turns in the primary coil
  • NS    amount of turns in the secondary coil                                        

PP = PS      (Assuming 100 % energy transfer, no energy dissipated in heating)

VP IP = VS IS

  • PP    power of the primary coil W (of VA)
  • IP     current in the primary coil in A
  • PS      power of the secondary coil  in W (of VA)
  •  IS       current  in the secondary coil  in A

Examples

  1.   The primary coil of a transformer consists of 400 turns. The secondary coil  

      80 turns.

      The voltage across the primary coil is 230 V

      Find the voltage across the secondary coil

      VP  :  VS  = NP :  NS

      230 : VS = 400 : 80

      230 : VS = 5 : 1

      5 Vs = (230)(1)

      VS = 230/5 = 46 V

2.    The primary coil is connected with an AC source

A bulb is connected with the secondary coil.

The voltage across the bulb is 6.0 V and

the current through the bulb is  0.4 A

The turns ratio is 5:1

 (NP : NS  = 5: 1)

Transformer

Calculate the current in the primary coil

        PS = VS IS = (6.0)( 0.4) = 2.4 W

        VP = 5 VS = (5 )(6.0) = 30 V

        PP = PS = 2.4 W

        PP = VP IP

             2.4 = 30 IP

             IP = 2.4/30 = 0.8 A   

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