112 Chapter 8 • Transformers


Te voltage per turn on the primary side is equal to the voltage per turn on the secondary side, i.e.,


V1 / N1 ∴ V1


___ V2


= V2 / N2 = N1


___ N2


................................... (b)


Combining (a) and (b) the transformer ratio becomes: V1


___ V2


Where V1


, N1 V2, N2 =


and I1 and I2


___ N2


N1


= __ I2


I2 ...................... (8.1)


refer to values on the primary side. refer to values on the secondary side.


N refers to number of turns.


In the case of three-phase transformers the above equation is still valid, but it is of utmost importance to remember that the values referred to are phase values.


Example 8.1


A single-phase transformer has 600 turns on the primary winding which is connected to a 220-V ac supply. Te voltage and current on the secondary side is 16,13 volts and 5 amperes respectively. Determine;


(a) the number of turns on the secondary side, (b) the value of the primary current, (c) the turns ratio, and (d) the voltage per turn.


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