section 17.4 transmission of electrical energy
TRANSCRIPT
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Section 17.4Section 17.4
Transmission ofTransmission of
electrical energyelectrical energy
Section 17.4Section 17.4
Transmission ofTransmission of
electrical energyelectrical energy Advantage of transmission ofAdvantage of transmission of
electrical energy with a.c.electrical energy with a.c.
source and transformersource and transformer
Power transmission systemPower transmission system
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Transmission of electrical energy with
d.c. source
17.4 Transmission of electrical energy (SB p. 170)
Expt. 17E
Transmission of
electrical energy
d.c.power
supply
BA
transmission line
http://movie/Expt%2017E/17E.avi -
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Transmission of electrical energy with
d.c. source
17.4 Transmission of electrical energy (SB p. 170)
12 V
d.c.
source
12 V
I
great power
loss in cable
bulb
is dim
great power loss in cablesPlost =I
2R
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Transmission of electrical energy with
a.c. source and transformers
17.4 Transmission of electrical energy (SB p. 171)
a.c.
source
BA step-up
transformer
step-down
transformer
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Transmission of electrical energy with
a.c. source and transformers
17.4 Transmission of electrical energy (SB p. 171)
Power loss in cables reduced
smaller current flowing in cables
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Example 5:Examp
le 5:The figure shows a transmission system. The total resistance
of the cables is 200 and the transformer is assumed to beideal. Find
(a) the current flowing in the cable, and
(b) the power loss in the cables.
Solut
ion
(b) ByP=I2RP= (0.25)2 200
= 12.5 W
A25.01001
25
25
By
A25200
0005
s
s
s
p
p
s
=
=
=
===
I
I
N
N
I
I
V
P(a) Current in primary coil (Ip)
17.4 Transmission of electrical energy (SB p. 172)
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Class Practice 4:Class Practice 4:A light bulb is connected to a 10 V a.c. power supply as
shown. The total resistance of the wires is 90 . Thecurrent drawn from the power supply is 0.1 A.
17.4 Transmission of electrical energy (SB p. 173)
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Class Practice 4: (Cont)Class Practice 4: (Cont)(a) (i) What is the input power in the transmission system?
Input power = _________________________
(ii)What is the power loss in the wires?
Power loss = __________________________
(iii)What is the efficiency of the power transmission?
Output power = ________________________
Efficiency = ____________________________
Ans
wer
17.4 Transmission of electrical energy (SB p. 173)
Answer
Ans
wer
Ans
wer
Input powerPower loss= 1 0.9 = 0.1 W
I2R = (0.1)2 90 = 0.9 W
VI= 10 0.1 = 1 W
%10%1001
1.0=
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Class Practice 4: (Cont)Class Practice 4: (Cont)(b) The same light bulb is connected to the same a.c. power
supply through transformers. Assume the transformers
are ideal ones and the current drawn from the a.c.
remains 0.1 A as before. What is the efficiency of the
power transmission?
The current in the
transmission wire
= ___________________________
Power loss in wires = __________________________
Efficiency = __________________________________
Ans
wer
I2R = (0.01)2 90 = 0.009 W
A01.01.010
1
=
%1.99%1001
009.01
=
17.4 Transmission of electrical energy (SB p. 173)
Ans
wer
Ans
wer
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Power transmission system
transmission system in Hong Kong
17.4 Transmission of electrical energy (SB p. 174)
step-up
transformer
at power
station
step-down
transformer
at zone
substations
step-down transformers
at local substations
400 kV or275 kV132 kV
33 kV 11 kV 380 V 220 V
heavy
industry
officeslight
industry homes and schools
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Useful WebsiteUseful Website
China Light & Power Company
(http://www.clpgroup.com
/clpgroup/CLPPower/FacServ)
The Hongkong Electric Co., Ltd.
(http://www.hec.com.hk/hec/hec/trans.htm)
17.4 Transmission of electrical energy (SB p. 175)
http://www.clpgroup.com/clpgroup/CLPPower/FacServhttp://www.clpgroup.com/clpgroup/CLPPower/FacServhttp://www.hec.com.hk/hec/hec/trans.htmhttp://www.hec.com.hk/hec/hec/trans.htmhttp://www.hec.com.hk/hec/hec/trans.htmhttp://www.hec.com.hk/hec/hec/trans.htmhttp://www.hec.com.hk/hec/hec/trans.htmhttp://www.hec.com.hk/hec/hec/trans.htmhttp://www.hec.com.hk/hec/hec/trans.htmhttp://www.hec.com.hk/hec/hec/trans.htmhttp://www.clpgroup.com/clpgroup/CLPPower/FacServhttp://www.clpgroup.com/clpgroup/CLPPower/FacServhttp://www.clpgroup.com/clpgroup/CLPPower/FacServhttp://www.clpgroup.com/clpgroup/CLPPower/FacServhttp://www.clpgroup.com/clpgroup/CLPPower/FacServ -
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Mind MapMind Map
Electromagnetic
induction
direction of induced current is governed by
conductor cuts magnetic field linesoccur either
magnetic field changes
17.1 Induced voltage
and induced
current
Faradays lawmagnitude of induced voltage is governed by
Lenzs lawtheory
transform voltage
step-up voltagefunction
17.3 Transformer
step-down voltage
voltage ratio / turns ratio
efficiency
s
p
s
p
N
N
V
V=
17.2 Generator d.c. generator
generate electricityfunction
applications
2 types
a.c. generator
17.4 Transmission of
electrical energy
use a.c. rather than d.c.
use high voltage rather than low
17.4 Transmission of electrical energy (SB p. 175)
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