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Equivalent Circuit diagram of single phase Transformer

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Equivalent circuit diagram of a transformer is basically a diagram which can be resolved into an equivalent circuit in which the resistance and leakage reactance of the transformer are imagined to be external to the winding.

The equivalent circuit diagram of transformer is given below:-

R1 = Primary Winding Resistance.
R2= Secondary winding Resistance.
I0= No-load current.
Iµ = Magnetizing Component,
Iw = Working Component,
This Iµ & Iw are connected in parallel across the primary circuit. The value of E1 ( Primary e.m.f ) is obtained by subtracting vectorially I1 Z1 from V1 . The value of X0 = E1 / I0 and R0 = E1 /Iw. We know that the relation of E1 and E2 is E2 /E1 = N2 /N1 = K , ( transformation Ratio )

From the equivalent circuit , we can easily calculate the total impedance of to transfer voltage, current, and impedance either to the primary or the secondary.

The secondary circuit is shown in fig-1. and its equivalent primary value is shown in fig- 2,





The total equivalent circuit of the transformer is obtained by adding in the primary impedance as shown in – Fig-3 .


And It can be simplified the terminals shown in fig – 4 & further simplify the equivalent circuit is shown in fig.- 5 ,


At last, the circuit is simplified by omitting I0 altogether as shown in fig- 5 .


From the equivalent circuit which is shown in fig.-3 , the total impedance between the input terminal is ,

This is so because there are two parallel circuits, one having an impedance of Zm and the other having Z’2 and Z’L in series with each other.


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