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. Where, R1 = Primary Winding Resistance. R2= Secondary winding Resistance.

1. Elementary Theory of an Ideal Transformer

2. E.M.F. Equation of a Transformer

3. Transformer on No-load
𝐼𝜇

4. as
so
so
Transformer on load
‘

5. Transformer on load
‘
ϕ1
ϕ2
ϕ1 ϕ1
ϕ2

6. Transformer on load
so

7. Transformer with Winding Resistance but No Magnetic Leakage

8. Equivalent Resistance

9. Equivalent Resistance

10. A transformer with
magnetic leakage is
equivalent to an ideal
transformer with inductive
coils connected in both
primary and secondary
circuits
Magnetic Leakage

11. Transformer with Resistance and Leakage Reactance
leakage reactances can also be transferred from one winding to the
other

12. Transformer with Resistance and Leakage Reactance

13. Prob: A 50-kVA, 4,400/220-V transformer has R1 = 3.45 W, R2 = 0.009 W.
The values of reactances are X1 = 5.2 W and X2 = 0.015 W. Calculate for
the transformer (i) equivalent resis- tance as referred to primary (ii)
equivalent resistance as referred to secondary (iii) equivalent reac- tance as
referred to both primary and secondary (iv) equivalent impedance as
referred to both pri- mary and secondary (v) total Cu loss, first using
individual resistances of the two windings and secondly, using equivalent
resistances as referred to each side.

15. Equivalent Circuit
𝐼𝜇
A:
B: Equivalent circuit of A:
𝐸1 = 𝑉1 − 𝐼1 𝑍1
𝑋0 =
𝐸1
𝐼0
; 𝑅0 =
𝐸1
𝐼 𝑤
𝐸2
𝐸1
=
𝑁2
𝑁1
= 𝐾

16. Equivalent Circuit
Secondary Circuit
Equivalent Primary values

17. Equivalent Circuit
Exact equivalent Circuit
Simplified circuit by
transferring the exciting
circuit across the
terminal

18. Equivalent Circuit
Further simplified by
omitting 𝐼0

19. Equivalent Circuit