1. Electromagnetism Notes-3
Electromagnetic Induction
The Transformer and its use in
the National Grid

2. Model National Grid-1

3. Model National Grid-1 Voltage IN /V Power of bulb /W Voltage OUT /V
2.5
0.75
0.9

4. Model National Grid-1 Voltage IN /V Power of bulb /W Voltage OUT /V
2.5
0.75
0.9
Voltage IN /V
Power of bulb /W
Voltage OUT /V 12 24
1.4

5. Model National Grid-2

6. Model National Grid-2 Voltage IN /V Power/W Turns ratio Step-up
V OUT /V
Step-down
V IN /V
Final
Voltage OUT /V
2.5
0.75
1 : 10 22 18
10 : 1
1.7

7. Model National Grid-2 Voltage IN /V Power/W Turns ratio Step-up
V OUT /V
Step-down
V IN /V
Final
Voltage OUT /V
2.5
0.75
1 : 10 22 18
10 : 1
1.7
Voltage IN /V
Power/W
Turns ratio
Step-up
V OUT /V
Step-down
V IN /V
Final
Voltage OUT /V 12 24
1 : 20
220
180
20 : 1
9.1

8. Inducing an emf without physical movement

9. Inducing an emf without physical movement-2

10. Magnetic circuit links electric circuits

11. Inducing an emf without physical movement-3

12. Faraday’s transformer 1831

13. Transformer principle-1

14. Transformer principle-2
Primary Turns
Secondary Turns
Input Voltage /V
Output Voltage /V 30 10
2.16
0.71 20
1.45
2.18 40
2.93 50
3.50 60
4.38

15. Questions Independent variable ? Kind of variable ?
Control variables ?
How does output voltage depend on Number of turns ?
Type of input voltage ?

16. Graph of Output Voltage /V against No. of turns
From graph, how does output voltage depend number of turns on secondary coil ?

17. The Transformer Equation

18. Energy Losses in a transformer
In practice, if the voltage is doubled the current is more than halved due to small energy losses in the transformer:-
The windings of copper wire do have resistance and heat is produced in them
The alternating magnetic flux induces currents in the core, Eddy currents, which cause heating in the iron core
The field lines in the core are repeatedly changed from one direction to the other and back again. This requires energy and also causes the core to get hot.
Leakage of field lines in the iron core reduces the output voltage and current

19. Step down transformer

20. Alternative National Grid model

21. Low voltage transmission

22. Efficiency of low voltage transmission
Voltage IN = 11.9 V
Voltage OUT = 1.4 V
Current IN = 2.79 A
Current OUT = 0.68 A
Power IN = 11.9 x 2.79
Power OUT = 1.4 x 0.68
= 15.6 W
= 1.1 W
Efficiency = Power IN / Power OUT
Efficiency = 1.1 / = 7%

23. High voltage transmission

24. Efficiency of high voltage transmission
Voltage IN = 12.5 V
Voltage OUT = 10.0 V
Current IN = 2.32 A
Current OUT = 1.60 A
Power IN = 12.5 x 2.32
Power OUT = 10.0 x 1.60
= 29.0 W
= 16.0 W
Efficiency = Power IN / Power OUT
Efficiency = 16 / 29 = 55%

25. Currents in an ideal transformer
For a transformer, with no energy losses, i.e. 100% efficient
Power IN = Power OUT
If the output voltage is doubled, the output current is halved.
A small current at high voltage delivers same power as large current at low voltage.
A power of 1000W can be delivered by Current of 10A at voltage 100V or Current of 1A at 1000V

26. Heating effect of a current
Much Greater heating effect with large current than with small current.
Power (W) = (Current in A)2 x Resistance (Ω)
10 fold increase in voltage leads to
10 fold decrease in current and a
100 times decrease in heat produced