Bab 2-DC MOTOR

7/26/2019 Bab 2-DC MOTOR

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DC MOTOR


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Motor Arus Terus

1.Konsep penukaran kuasa elektrik kepada

kuasa mekanikal2.Prinsip kendalian motor a.t.

3.Tindak balas angkir, menukar arah putaran

motor dan daya gerak elektrik balikan

4.Motor jenis siri, pirau dan gabungan

5.Perbandingan ciri-ciri motor a.t.

6.Persamaan voltan motor a.t.

7.Daya kilas angkir dan daya kilas aci

8.Mengawal kelajuan motor a.t.

9.Pengaturan kelajuan10.Kehilangan dan kecekapan

11.Penghidup motor a.t.

12.Kegunaan motor a.t.


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Introduction

Electromagnetic Energy Conversion:

1. When armature conductors move in a magnetic field produced

by the current in stator field winding, voltage is induced in the

armature conductors.

2. When current carrying armature conductors are placed in a

magnetic field produced by the current in stator field winding,the armature conductors experience a mechanical force.

hese two effects occur simultaneously in a !C machine

whenever energy conversion ta"es place from electrical to

mechanical or vice versa.


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Operation Of DC Motor

Flemmingleft handrule


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Armature Reaction

#f a load is connected to the terminals of the dc

machine, a current will flow in its armature windings.

his current flow will produce a magnetic field of itsown, which will distort the original magnetic field from

the machine$s field poles. his distortion of the magnetic

flux in a machine as the load is increased is called the

armature reaction.


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Reversal of Direction of Rotation:

The direction of the magnetic ux in the air gap depends onthe direction of the eld current.

And the direction of the force exerted on the armaturewinding depends on the direction of ux and the direction ofarmature current.

Thus in order to reverse the direction of dc motor, we haveto reverse the direction of force.

This can be achieved either by changing the terminalsof the armature or the terminals of the eld winding

Reversal of Direction ofRotation:


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DC Motor Operation

In a dc motor, the statorpoles are supplied by dcexcitation current, whichproduces a dc magnetic

field. The rotor is supplied by dc

current through the brushes,commutator and coils.

The interaction of themagnetic field and rotorcurrent generates a forcethat drives the motor


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DC MachineEuivalent

Circuit


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Euivalent circuit of a DC motor

The armature circuit theentire rotor structure! isrepresented "# an idealvoltage source EAand a

resistor RA. A "atter# Vbrushin

the opposite to a current owin the machine directionindicates "rush voltage drop.The eld coils producing themagnetic ux are represented"# inductor LFand resistor RF.

The resistor Radjrepresents an

external varia"le resistorsometimes lumped togetherwith the eld coil resistance!used to control the amount of

current in the eld circuit.


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The armatureis represented "# an ideal voltage source EAand aresistor RA.

The brush voltage dropis represented "# a small "atter# Vbrushopposing the direction of the current ow in the machine.

The feld coils, which produce the magnetic ux, arerepresented "# inductor LFand RF.

The separate resistor Radjrepresents an external variableresistorused to control the amount of current in the eld circuit.

D$ %otor &'uivalent $ircuit.

&'uivalent $ircuit of a D$ %otor.


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The brush drop voltageis often onl# a ver# tin# fraction of thegenerated voltage in the motor.

Therefore, in cases where it is not critical, the "rush drop voltagema# "e left out or approximatel# included in the value of RA.

Also, the internal resistance of the led coils is sometimeslumped together with the varia"le resistor, and the total is calledRF, Figure "elow.

A (implied &'uivalent $ircuit eliminating the )rush*oltage Drop and $om"ining Rad+with the Field

Resistance .


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The &'uivalent $ircuit of (eparatel# &xcited dc %otor.

From the a"ove gure,

%otor t#pes: (eparatel# &xcited D$motors.

!eparately e"cited DCmotor:a eld circuit is supplied froma

separate constant voltagepower source.

F

FF

R

VI =

AAAT RIEV +=

AL II =


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The Euivalent Circuit ofa !hunt dc Motor#

From the a"ove gure,

%otor t#pes: (hunt D$ motors.

!hunt DC motor:a eld circuit gets its powerfrom the armature terminals ofthe motor.

F

FF

R

VI =

AAAT RIEV +=

FAL III +=


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Motor types:The permanentmagnetD$ motor

A permanent magnet D$ -%D$! motor is a motor whose polesare made out of permanent magnets.

Advantages:

. (ince no external eld circuit is needed, there are no eld circuitcopper losses/

0. (ince no eld windings are needed, these motors can "econsidera"le smaller.

Disadvantages:

. (ince permanent magnets produceswea1er ux densities then externall#

supported shunt elds, such motors havelower induced tor'ue.

0. There is alwa#s a ris1 of demagneti2ationfrom extensive heating or from armaturereaction e3ects via armature mmf!.


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Motor types: The series DC motor

A series D$ motor is a D$ motor whose eld windings consistsof a relativel# few turns connected in series with armaturecircuit. Therefore:

( )SAAAT RRIEV ++=


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Motor types: Compounded DC motor

A compounded D$ motor is a motor with "oth a shunt and aseries eld.

4ongshuntconnection

(hortshuntconnection

$urrent owing into adotted end of a coilshunt or series!produces a positive mmf.

5f current ows into thedotted ends of "oth coils,the resulting mmfs addto produce a larger totalmmf 6 cumulativecompounding.5f current ows into the dotted endof one coil and out of the dottedend of another coil, the resultingmmfs su"tract 6 di3erentialcompounding.


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Motor types: Compounded DC motor

The 7irchho38s voltage law e'uation for a compounded D$ motor is

The currents in a compounded D$ motor are

The mmf of a compounded D$ motor:$umulativel# compounded

Di3erentiall# compoundedThe e3ective shunt eld current in a compounded D$ motor:

9um"er of turns

.;.!

.;.0!

.;.

.;.=!

.;.!

( )SAAAT RRIEV ++=

FLA III =F

TF

R

VI =

ARSEFnet FFFF =

F

ARA

F

SEFF

N

FI

N

NII +=%


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Torue Euation

T> tor'ue of armature 9m!

1A> geometr# constant

> ux?pole @"!IA> armature current A!

AA IkT =


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$eometry Constant

p> num"er of eld polesN> num"er of active conductors on armature

M> num"er of parallel paths in armature winding>p for lap winding, >0 for wave winding!

&'()

&,*'2

+ rpmM

pNksrad

M

pNk AA ==


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%ower Euation

P=power @! 6 not counting lossesE > &%F induced in armature "ac1 &%F!IA> armature current A!

T> tor'ue of armature 9m! > speed of rotation rad?s!

9ote that -in> *454which will "e higher than -"ecause of loss in the eld and armaturewindings as well as rotational friction! losses.

TEIP A==


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EM& Euation

E > &%F induced in armature *!1A> geometr# constant

> ux?pole @"!

> speed of rotation rad?s!

n> speed of rotation of armaturerpm!

nkkE AA +==

2

()=n


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Terminal 'oltage Euation

*T> voltage at motor terminals

E > &%F induced in armature *!

IA> armature current A!

RA> armature resistance

E

-

-

/0

AAT RIEV +=


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!peed Euation

applies to shunt connected motor onl#!

9ote that can also "e written as 1f5fwhere

1fis ?5

fnormall# a constant ratio!

Ratio &'uation

+

A

AAT

k

RIVn

=

1

2

1

2

E

E

n

n=


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!peed(Torue

orue

peed

eries

hunt

Cumulative Compound

!ifferential Compound


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%ower )ow and losses in DC machines

nfortunatel#, not all electrical power is converted to mechanical power"# a motor and not all mechanical power is converted to electrical power"# a generatorB

The eCcienc# of a D$ machine is:

or

31))xP

PP

in

lossin

=

31))xP

P

in

out=


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The losses in DC machines

There are vecategories of losses occurring in D$ machines.

. &lectrical or copper losses 6 the resistive losses in the armatureand eld windings of the machine.

Armature loss:

Field loss:

@here IAand IFare armature and eld currents and RAand RF are

armature and eld winding! resistances usuall# measured at normaloperating temperature.

AAA RIP

2

=FFF RIP

2=


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The losses in DC machines

0. )rush drop! losses 6 the power lost across the contact potential atthe "rushes of the machine.

@here IAis the armature current and VBDis the "rush voltage drop. The

voltage drop across the set of "rushes is approximatel# constant over alarge range of armature currents and it is usuall# assumed to "e a"out 0*.

ther losses are exactl# the same as in A$ machinesB

ABDBD IVP =

Th l i DC


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The losses in DCmachines

=. %echanical losses6 losses associated with mechanical e3ects:friction friction of the "earings! and windage friction "etween themoving parts of the machine and the air inside the casing!. These lossesvar# as the cu"e of rotation speed n.


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The power()ow diagram

n of the most convenient techni'ue to account for powerlosses in a machine is the powerow diagram.

For aD$

motor:

&lectrical power is input to the machine, and the electrical and "rushlosses must "e su"tracted. The remaining power is ideall# converted fromelectrical to mechanical form at the point la"eled as P%onv.


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The power()ow diagram

The electrical power that is converted is

And the resulting mechanical power is

After the power is converted to mechanical form, the stra# losses,

mechanical losses, and core losses are su"tracted, and the remainingmechanical power is output to the load.

AAconv IEP =

mindconvP =


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E"ample *

A pole, G.G m@",eld winding current is .0GA. Find the speed and tor'ue.

AAAIII FLA 4.252.126 ===

( ) ( ) VAVRIVE AAT 1)276.)4.2512) ===

( ) ( )( ) ( )

165(2

8()(

2===

M

pNA

( ) ( ) srad

x

V

E

E

A

A

*8.((1)1)165

1)2

5 ===

=

rpmn (542

()=

=

( ) k!"p

!"pP 29.2

79(5 =

=

mNsrad

k!PT === 6.55

*8.((

29.2


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E"ample +

A Ghp, * Dc series motor ta1es =GA at its full load speedof ;GGrpm. @hat is the tor'ue at


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E"ample , -a.

A 00G* D$ shunt motor draws GA at ;GGrpm. Thearmature resistance is G.0and eld winding resistance is==G.

a! @hat is the tor'ueJ

AV

R

VI

F

TF 6.)

99)

22)=

==

AAAIII FLA 6.86.)1) ===

( ) ( ) VAVRIVE AAT 2142.)6.822) ===

( ) ( ) k!AVEIP A )7.26.8214 ===

( )srad

n*144

()

14))2

()

2===

mNsrad

k!PT === ).11

*144

)7.2


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E"ample , -b.

A 00G* D$ shunt motor draws GA at ;GGrpm. Thearmature resistance is G.0and eld winding resistance is==G.

"! @hat will "e the speed and line current at a tor'ue of 0G9m if eld current is constant!J

'shunt is constant speed&

1(.1*144

214===

=

srad

VE

E

A

A

AmN

TI

IT

A

A

AA

5.171(.1

2)=

==

=

AAAIII FAL 4.176.)5.17 =+=+=

( ) ( ) VVRIVE AAT 2172.)5.1722) ===

rpmxn

sradV

E

A

51)78.1

2

()

*147

1(.1

217

==

===

Bab 2-DC MOTOR

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