The document discusses phasor diagrams and equivalent circuits of transformers. It presents phasor diagrams showing the relationship between voltages and currents for transformers under no load, unity power factor load, lagging power factor load, and leading power factor load conditions. It then derives the equivalent circuit models of transformers by representing the transformer components like winding resistances and leakage fluxes as circuit elements. The equivalent circuits are developed with parameters referred to both the primary and secondary sides. Approximate equivalent circuits neglecting the no-load current are also presented.

1. TRANSFORMER- PHASOR DIAGRAM,
EQUIVALIENT CIRCUIT
PHASOR DIAGRAM AND EQUIVALIENT CKT KNCET 1
Content:
 Introduction to load and no load with lagging and leading power
factor .
 Different types of leakage flux and steps to minimize the leakage
fluxes.
 References

2. 2
Phasor diagram: Transformer on No-
load
PHASOR DIAGRAM AND EQUIVALIENT CKT KNCET

3. Transformer on load assuming no
voltage drop in the winding
Fig shows the Phasor diagram of a transformer
on load by assuming
1. No voltage drop in the winding
2. Equal no. of primary and secondary turns
3PHASOR DIAGRAM AND EQUIVALIENT CKT KNCET

4. Transformer on load
Fig. a: Ideal transformer on load
Fig. b: Main flux and leakage
flux in a transformer
4PHASOR DIAGRAM AND EQUIVALIENT CKT KNCET

5. Phasor diagram of transformer with
UPF load
5PHASOR DIAGRAM AND EQUIVALIENT CKT KNCET

6. Phasor diagram of transformer with
lagging p.f load
6PHASOR DIAGRAM AND EQUIVALIENT CKT KNCET

7. Phasor diagram of transformer with
leading p.f load
7PHASOR DIAGRAM AND EQUIVALIENT CKT KNCET

8. Equivalent circuit of a transformer
No load equivalent circuit:
8PHASOR DIAGRAM AND EQUIVALIENT CKT KNCET

9. Equivalent circuit parameters referred to
primary and secondary sides respectively
9PHASOR DIAGRAM AND EQUIVALIENT CKT KNCET

10. Contd.,
• The effect of circuit parameters shouldn’t be changed while
transferring the parameters from one side to another side
• It can be proved that a resistance of R2 in sec. is equivalent
to R2/k2 will be denoted as R2’(ie. Equivalent sec. resistance
w.r.t primary) which would have caused the same loss as R2
in secondary,
2
2
2
2
1
2'
2
2
2
2
'
2
2
1
k
R
R









R
I
I
RIRI
10PHASOR DIAGRAM AND EQUIVALIENT CKT KNCET

11. Transferring secondary parameters to
primary side
11PHASOR DIAGRAM AND EQUIVALIENT CKT KNCET

12. Equivalent circuit referred to
secondary side
•Transferring primary side parameters to secondary side
Similarly exciting circuit parameters are also transferred to
secondary as Ro’ and Xo’
12PHASOR DIAGRAM AND EQUIVALIENT CKT KNCET

13. equivalent circuit w.r.t primary
where
13PHASOR DIAGRAM AND EQUIVALIENT CKT KNCET

14. Approximate equivalent circuit
• Since the noload current is 1% of the full load
current, the nolad circuit can be neglected
14PHASOR DIAGRAM AND EQUIVALIENT CKT KNCET

15. 15PHASOR DIAGRAM AND EQUIVALIENT CKT KNCET
Conclusion:
• Phasor diagram for different load condition is explained in detail with
suitable diagrams.
• Equivalent circuit also drawn with primary and secondary parameters.
References:
1.P. C. Sen., ‘Principles of Electrical Machines and Power Electronics’, John
Wiley & Sons, 1997.
2.P.S. Bimbhra, ‘Electrical Machinery’, Khanna Publishers, 2003.
3.S.Sarma & K.Pathak “Electric Machines”, Cengage Learning India (P) Ltd.,
Delhi, 2011.
4.U.A.Bakshi&M.N.Bakshi “Electric Machines-I”,Technical
publications,2015.
5.Other Web Sources