electromagnet 8.4

8/15/2019 Electromagnet 8.4

1/11

FORM 5© COPYRIGHT BY SUPER EDUCATION GROUP (J

CHAPTER 8: Electr!"#$et8%& Tr"$'r!er


2/11

CHAPTER 8: Electr!"#$et

8.4: Transformers

1. In Malaysia, our electricity for domestic supplied at a voltage of ……………… a.c.

2. However, most of home appliances at home use lower than or higher than 240.!. "ransformers are found in many devices such as ………………., …………………., …………………..

and etc.

4. "he main use of transformer is to convert ……………………. #$ oltage to ……………. one or vice%

versa.

# transformer is a device which step ups or steps down alternating current voltage

Operating principle of a transformer

&. 'ased on the electromagnetic induction, the a.c voltage is applied to the primary coil of a transformer,

an alternating current flow through the circuit.

(. )hen an alternating current flows in primary coil, and magnetic field is produced in the soft iron core.

*. Magnetic flu+ linage to secondary coil and will cut the magnetic fields lines.

-. "he secondary coil e+periences the rate of change of magnetic field and current is induced in secondary

coil. induced e.m.f /

. )hen the current in primary coil decreases, the magnetic field will collapse and again cut the secondary

coil.

10. #n e.mf acting in the opposite direction is induced in the secondary coil.

11. Hence, an alternating e.m.f of the same freuency is induced in the secondary coil.

12. "he output voltage is depends on the ratio of numer of turns of primary and secondary coils.

PREPARED BY JJ MREON P"#e *© COPYRIGHT BY SUPER EDUCATION GROUP (JOHOR JAYA)

240 V

mobilelaptopstelevision

small larger

Laminated soft-iron

OUTPUTINPUT

SecondaryPrimary coil

ymbol of


3/11


Step-up and step-down transformers

1. "he relationship etween the voltages and the ratio of the turns in primary and secondary coils can e

If Ns is greater than Np, then Vs is ………………… than Vp. "he type of transformer is

………………………….

If Ns is less than Np, then Vs is ………………… than Vp. "he type of transformer is

………………………….

3or e+ample, if the turns ratio is 1&0, the output voltage is stepped up ……….. times.

PREPARED BY JJ MREON P"#e +© COPYRIGHT BY SUPER EDUCATION GROUP (JOHOR JAYA)

N,!-er t,r$' .$ /r.!"r0 c.l

N,!-er t,r$' .$ 'ec$1"r0=

Pr.!"r0 2lt"#e

Sec$1"r0

=Vs

Ns

Vp

Np

Np

Ns

Vp

Vs= OR

less

step-!p

step-do#n

tep-!ptep-do#n


4/11


PREPARED BY JJ MREON P"#e 3© COPYRIGHT BY SUPER EDUCATION GROUP (JOHOR JAYA)


5/11


Energy losses in a transformer

#s we now, an ideal transformer has ………….. effiency.

'ut in practice, the efficiency of a tranformer is …………….. 1005.

"he effiency of a transformer is e+pressed as follows

PREPARED BY JJ MREON P"#e &© COPYRIGHT BY SUPER EDUCATION GROUP (JOHOR JAYA)

Po#er !sed in

the secondary=Po#er s!pplied

to the primary

=

Vp

Vs=

Is

Ip

VpI

p

VsIs

C!/"r.$# 4.t te

tr"$'r!er e6,"t.$Is

Ip

Np

Ns=

$00%

less than

1005

1005

Pout

Pin

VsIs

VpIp

η = ×

= ×


6/11


13. $omplete the tale elow

Type of losses Causes Way to reduce

Eddy current • current induced in the core due to

electromagnetic induction.

• $hanging of magnetic field induced

current in soft iron core

Eddy current produced and generate

heat

Use laminated core

higher resistance to reduce eddy

current

Heat loss • #s the numer of turn increases, the

resistance of conductor also increases.

Heat produced by electrical energy to

oppose the resistance

Use low resistance copper

/aluminium wires

Thick wire to reduce resistance

Hysterisis loss

/magnetism and

demagnetizatio

n of the core

• "he core is magneti6ed and

demagneti6ed alternately due to a.c

current in primary coil

Energy loss as heat

Use soft-iron core

t is able to be magnetized and

demagnetized easily

3lu+ leaage • 7eaage of magnetic flu+ in the

primary coil

!roper core design

wind the primary coil on the top of

the secondary coils

PREPARED BY JJ MREON P"#e 5© COPYRIGHT BY SUPER EDUCATION GROUP (JOHOR JAYA)


7/11


9/11

He"20 .$1,'tr0

.#t .$1,'tr0

1 kV

B,.l1.$#'

240 V

M0 ,'e


8.: !eneration and Transmission of Electricity

Sources of Energy

1. "he generation of electricity comes from many sources such as

"% H01r

-% G"'e'c% N,cle"r1% D.e'ele% C"l% B.!"''#% Sl"r% 9.$1

"ational !rid "etwor#

2. 8ational 9rid 8etwor is a networ of underground cales or …………… which connect all the power

stations and sustations for the whole country.!. "his networ starts at electrical power plant lie $henderoh 7ae :ower ;tation which is hydroelectric

power station, and end at our houses.

4. $omplete the diagram elow y showing the cales of transmission and suitale users.

&.


10/11

132 kV


2

heat P I R=

*. "he power loss can reduce y

i. =educing the ……………………… of the cales

ii. =educing the current or ……………………. the voltage in the cale.

#dvantages of use national grid networ

1. easy to manage =egional control and switching centres enale power to

e sent where and when it is needed.

2. 7ess interruptions and continuously =egional control and switching centres allow some

stations and lines to e shut down for maintenance wor

without cutting off the supply to the consumers

!. =educing cost of generation High voltage transmission can reduce the power loss in

transmission cales. "he cost production is reduced.

4. uring periods of low

demand, some generators can e turned off.

$enewa%le energy

=enewale energy sources are continually replenished naturally means they are sustainale.

&. 9ive the e+ample of renewa%le energy

I% H01relectr.cII% Sl"rIII% 9.$1I% Geter!"l

% B.!"''I% 9"2eII% T.1"l

(. 9ive the e+ample of non-renewa%le energy

i. ……………………..

a& 'ilb& (asc& )oal

*. 9ive the enefits of using the renewale energy to our nation

PREPARED BY JJ MREON P"#e ;© COPYRIGHT BY SUPER EDUCATION GROUP (JOHOR JAYA)

I < c,rre$t =4' .$ te c"-le

R < re'.'t"$ce te c"-le

resistance

increasing

F''.l ,el ',c


11/11

33 >

tr"$'!.''.$


a* +void depletion of fossil f!elsb* )leaner so!rces for little poll!tionc* +void harming ,ora and fa!nad* +void the disr!ption of ecological balance

PREPARED BY JJ MREON P"#e *?© COPYRIGHT BY SUPER EDUCATION GROUP (JOHOR JAYA)

electromagnet 8.4

Documents