1. Electrical Machines (EELE 3351)

2. Assad Abu-Jasser, PhD Electric Power Engineering The Islamic University of Gaza

3. Chapter 2
Transformers

5. Electric Transformer Animation

6. Transformer Types and Construction
Core-Type
Shell-Type

7. The Ideal Transformer

8. Power in an Ideal Transformer
Output Power
Input
Power

9. Impedance Transformation Through a Transformer

10. Ideal Transformers Circuits Analysis (Example 2.1)
A generator rated at 480-V, 60-Hz is connected a transmission line with an impedance of 0.18+j0.24 Ω. At the end of the transmission line there is a load of 4+j3 Ω.
If the power system is exactly as described above in Figure (a), what will the voltage at the load be? What will the transmission line losses be?
Suppose a 1:10 step-up transformer is placed at the generator end of the transmission line and a 10:1 step-down transformer is placed at the load end of the line (Figure (b)). What will the load voltage be now? What will the transmission line losses be now?

11. Single-Phase Transformers Theory of Operation

12. Transformer Voltage Ratio

13. Transformer Current Ratio Dot Convention

14. Example 2.1
An ideal transformer has a 150-turn primary and 750-turn secondary. The primary is connected to a 240-V, 50-Hz source. The secondary winding supplies a load of 4 A at a lagging power factor of 0.8, Determine (a) the a-ratio, (b) the current in the primary, (c) the power supplied to the load

15. Transformer Equivalent Circuit
Copper (I2R) Losses - Resistive heating losses
Eddy current Losses - resistive heating losses in the core
Hysteresis Losses - due to the magnetic domains
Leakage flux - the fluxes which escape the core

16. Transformer Exact Equivalent Circuit

17. Approximate Equivalent circuits

18. Transformer Voltage Regulation

19. Transformer Phasor Diagram
Simplified Voltage Regulation Calculation

20. Transformer Efficiency

21. Example 2.2
A 23-kVA, 2300/230-V, 60-Hz, step-down transformer has the following resistance and leakage-reactance values: R1=4Ω, R2=0.04Ω, X1=12Ω, and X2=0.12Ω. The equivalent core-loss resistance and the magnetizing reactance on the primary side of the transformer are 20 kΩ and 15kΩ, respectively The transformer is operating at its rated voltage and rated load. If the power factor of the load is lagging, determine the efficiency of the transformer and plot the phasor diagram.

22. The Autotransformer

23. V-I Relations in an Autotransformer

24. The Autotransformer Rating

25. Example 2.7
A 100-VA, 120/12-V transformer is to be connected so as to form a step-up autotransformer as shown. A primary voltage of 120 V is applied to the transformer. (a) what is the secondary voltage of the transformer, (b) what is the maximum volt-ampere rating in this mode of operation?, and (c) calculate the rating advantage of this autotransformer connection over the conventional 120/12-V operation.

26. Three-Phase Transformer
3 Single-Phase Transformers
1 Three-Phase Transformer

27. 3-Phase Transformer Connections

28. Example 2.9
A 50-kVA, 13800/208-V, ∆-Y distribution transformer has a resistance of Ω/phase and a reactance of 800Ω/phase referred to the high voltage side. (a) what is the transformer phase impedance referred to the low voltage side, and (b) calculate the voltage regulation at full-load and 0.8 PF lagging.

29. End Of
Chapter Two