Section 17.4 Transmission of Electrical Energy

8/14/2019 Section 17.4 Transmission of Electrical Energy

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Manhattan Press (H.K.) Ltd. 1

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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d.c. source


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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a.c. source and transformers


a.c.

source

BA step-up

transformer

step-down

transformer


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a.c. source and transformers


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)



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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.



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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


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

=


Ans

wer

Ans

wer


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Power transmission system

transmission system in Hong Kong


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)

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



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Section 17.4 Transmission of Electrical Energy

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