#### Transcript eletran

```ELECTROMAGNETIC
INDUCTION
TRANSMISSION OF
ELECTRICAL ENERGY
1
Transmission of
Electrical Energy
a.c.
power
supply
Step-up
transformer
cables
Step-down
transformer
2
Power Supply
A.C. Generator
(alternator)
Kinetic Energy
D.C. Generator
(d.c. dynamo)
Electrical Energy
3
A.C. Generator
4
A.C. Generators
• Induced current is the maximum
when the plane of the coil is
horizontal, because the rate of
cutting the magnetic field lines is
highest.
• The direction of the induced current
is reversed for each half revolution
of the coil.
http://home.a-city.de/walter.fendt/physengl/generatorengl.htm
5
E.m.f. generated
The e.m.f. generated at the generators
can be increased by :
(i) Rotating the coil at a higher speed,
(ii) Increasing the number of turns of
the coil,
(iii)Winding the coil on a soft-iron core
(armature), and
(iv) Using a stronger magnet.
6
D.C. Generator
7
Transformer
How does the brightness of the lamp in primary
circuit compared with that of the lamp in
secondary circuit?
8
Transformer I
picture
9
Transformer II
INPUT
Energy Source
(a.c. supply)
OUTPUT
Primary
Coil
Secondary
Coil
e.g. Light Bulb
10
Transformer III
• The a.c. in the primary coil sets up
an alternating magnetic field in the
coil.
• An alternating e.m.f. and current of
the same frequency are induced in
the secondary coil continuously.
• The light bulb connected to the
secondary coil of more turns is
brighter than that connected to the
secondary coil of fewer turns.
11
Transformer IV
Vs
Ns
=
Vp
Np
Where
Vp is the input voltage or primary voltage,
Vs is the output voltage or secondary voltage,
Np is the number of turns in the primary coil,
Ns is the number of turns in the secondary coil.
12
Step-up and Step-down
transformer
13
Transmission of electricity
without transformer
• Plost = I2 R
• where I is the current in the cable and R is
the resistance of the cable.
• The power loss is great when electricity is
transmitted through long cables.
14
Transmission System with
transformers
15
Transmission System
• For an ideal transformer,
• Output Power = Input Power
• Vs Is = Vp Ip &
Is = (
• Power loss at the cable = Is2 R
Vp
Vs
) Ip
• Is is greatly reduced and power loss
at the cable would be much reduced
if Vs>>Vp .
16
Transmission of
electrical energy
• High voltage transmission reduces
the energy lost in the cable as heat.
• An a.c. power supply is used instead
of a d.c. power supply because a.c.
can easily be stepped up and
stepped down by using transformers
with negligible energy loss.
17
Transmission System in
Hong Kong (I)
18
Transmission System in
Hong Kong (II)
•
•
•
•
•
http://www.hec.com.hk
(The Hongkong Electric Co., Ltd.)
http://www.clpgroup.com
http://www.chinalightandpower.com.hk
(The CLP Holdings Ltd.)
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THE END
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```