4. Transformer equivalence circuit.pptx

ransformer equivalence circuit.pptx from K nsitu

1. Transformers equivalent circuit

2. Outline Exact equivalent circuit Approximate Equivalent Circuit

3. Equivalent Circuit of a transformer The equivalent circuit enables us to analyze and predict the performance of the transformer by using electric circuit theory. Exact Equivalent Circuit At no-load the current is used to create the magnetic flux and to supply the core losses. The magnetizing current lags the voltage E1 by 90 o while the core loss current is in phase with E1 Thus the phasor diagram of the magnetizing branch is shown in Figure

4. Equivalent Circuit of a transformer

5. Exact Equivalent Circuit At no-load the effect of magnetizing the core is represented by a fictitious inductive reactance called magnetizing reactance ( ) across the emf E1 Core losses are represented by a fictitious resistance called the core loss resistance ( )  

6. Exact Equivalent Circuit When the transformer is on load, secondary current flows causing the primary current to increase over the no-load current. In the equivalent circuit the primary and secondary winding resistances are represented by and respectively. The corresponding copper losses are  

7. Exact Equivalent Circuit The effects of flux leakages are represented by leakage reactances and in series with the primary and secondary winding resistances respectively. The exact equivalent circuit of the double wound transformer is shown in the figure below.  

8. Exact Equivalent Circuit It is composed of the primary winding series impedance ,the magnetizing impedance and the secondary winding series impedance

9. Exact Equivalent Circuit

10. Exact Equivalent Circuit

11. Exact Equivalent Circuit

12. Approximate Equivalent Circuit The circuit of Fig 9 can be simplified by connecting the magnetizing branch across the supply to obtain the approximate equivalent circuit shown in Fig 11. This increases the value of the no-load current and core losses slightly while reducing the voltage drop across the series impedance ( ) and the copper power loss in the primary winding slightly. Why?

13. Approximate Equivalent Circuit

14. Approximate Equivalent Circuit

15. Approximate Equivalent Circuit

16. Approximate Equivalent Circuit

17. Approximate Equivalent Circuit

18. Approximate Equivalent Circuit

19. Approximate Equivalent Circuit

20. 4 kVA, 3200/320 V, 50 Hz step-down single phase transformer has primary winding and secondary winding resistance of 1.25 Ω and 0.0125 Ω respectively. The primary winding and secondary winding reactances are 3.75 Ω and 0.0375 Ω respectively. Determine: The equivalent resistance referred to the primary winding The equivalent resistance referred to the secondary winding