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OPERATION OF A DC OPERATION OF A DC

GENARATORGENARATOR

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ENERGY CONVERSION INENERGY CONVERSION IND.C. GENERATORD.C. GENERATOR

INPUTINPUT OUTPUT OUTPUT

MECHANICAL ENERGYMECHANICAL ENERGY ELECTRICAL ELECTRICAL ENERGY ENERGY

D.C. GENERATOR

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ENERGY CONVERSION INENERGY CONVERSION IND.C. MOTORD.C. MOTOR

INPUTINPUT OUTPUT OUTPUT

ELECTRICAL ENERGYELECTRICAL ENERGY MECHANICA MECHANICA ENERGYENERGY

D.C. MOTOR

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What is the device which generates What is the device which generates Electrical Energy ?Electrical Energy ?

• GeneratorGenerator

A generator converts __________ energy to A generator converts __________ energy to

__________ energy.__________ energy.

Mechanical

Electrical

MechanicalEnergy

Electrical Energy

Generator

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What are the basic requirements What are the basic requirements generating EMF generating EMF ??

• ConductorConductor

• Magnetic FieldMagnetic Field

• Relative SpeedRelative Speed

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How EMF is Induced ?How EMF is Induced ?

When ever a conductor cuts the Magnetic field an When ever a conductor cuts the Magnetic field an EMF is induced in it ( Faradays IEMF is induced in it ( Faradays Istst law of Electro law of Electro magnetic induction )magnetic induction )

What are the types of Induced EMF ?What are the types of Induced EMF ?

Dynamically Induced EMFDynamically Induced EMF Self Induced EMFSelf Induced EMF

What do you mean my the word Dynamics ?What do you mean my the word Dynamics ?

Dynamics is related to motionDynamics is related to motion

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DYNAMICALLY INDUCED EMFDYNAMICALLY INDUCED EMF

Emf is induced when the Emf is induced when the flux linking a conductor flux linking a conductor changeschanges

In dynamically induced In dynamically induced emf , the conductor emf , the conductor moves in a stationary moves in a stationary magnetic field.magnetic field.

The emf is induced in the The emf is induced in the conductor when it is in conductor when it is in motionmotion

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Fig. 1. DYNAMICALLY INDUCED EMF

Poles

Conductor

Field

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FLEMINGS RIGHT HAND RULEFLEMINGS RIGHT HAND RULE

Thumb points motion

Forefinger points field

Middle finger points Induced EMF

Important parts of D.C. GeneratorImportant parts of D.C. Generator

YokeYoke

Pole core and pole shoePole core and pole shoe

Field coilsField coils

Armature coreArmature core

Armature windingArmature winding

CommutatorCommutator

Brushes and brush holdersBrushes and brush holders

BearingsBearings

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N

N

SS

HOOK

FIELD WINDINGPOLE

ARMATURE

BASE

COMMUTATOR

YOKE

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YokeYoke

Yoke is the outermost Yoke is the outermost cylindrical frame as cylindrical frame as shown in Fig.1shown in Fig.1

It is made up of cast ironIt is made up of cast iron

It provides the low It provides the low reluctance path to reluctance path to magnetic fluxmagnetic flux

Fig.1

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Yoke of Small machineYoke of Small machine

Pole core and Pole shoePole core and Pole shoe

Pole core is made-up of Pole core is made-up of cast iron as shown in cast iron as shown in Fig.2Fig.2

Pole shoe is made-up of Pole shoe is made-up of cast iron laminationscast iron laminations

Pole shoe supports the Pole shoe supports the field coils and spreads field coils and spreads the magnetic flux in the the magnetic flux in the air- gapair- gap

Fig.2

EE-303.6EE-303.6 1515Pole Shoe

Field CoilsField Coils

Field coils are made-up of Field coils are made-up of enamel coated copper or enamel coated copper or aluminum wire as shown aluminum wire as shown in Fig.3 in Fig.3

Placed on pole core Placed on pole core

Produces flux when Produces flux when excitedexcited

Fig.3

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Construction of Simple Loop GeneratorConstruction of Simple Loop Generator

A simple loop A simple loop generator isgenerator is

Single turn Single turn rectangular rectangular copper coilcopper coil

Placed between Placed between poles of a poles of a magnetmagnet

Used to study Used to study the generation the generation of emf in D.C. of emf in D.C. generatorgenerator

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SIMPLE LOOP GENERATORSIMPLE LOOP GENERATOR

Fig.1

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WORKING OF SIMPLE LOOP GENERATORWORKING OF SIMPLE LOOP GENERATOR Consider a single turn rectangular copper coil is rotating Consider a single turn rectangular copper coil is rotating

in a magnetic field.in a magnetic field.

The coil occupies different angular positions during its The coil occupies different angular positions during its rotation.rotation.

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When the coil is rotated through an angle of 90° When the coil is rotated through an angle of 90° the emf induced in the coil is maximum.the emf induced in the coil is maximum.

Rotate the coil further by an angle of 180°.The Rotate the coil further by an angle of 180°.The emf induced in the coil will be zero.emf induced in the coil will be zero.

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Rotate the coil further by an angle of 270°.The Rotate the coil further by an angle of 270°.The emf induced in the coil is maximum in the emf induced in the coil is maximum in the reverse direction.reverse direction.

We conclude that the nature of the emf induced We conclude that the nature of the emf induced

is alternating.is alternating.

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N S

B

A

D

C

R

b1

b2s1

s2

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N S

B

A D

C

R

b1

b2s1

s2

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N S

C

D

A

B

R

b1

b2s1

s2

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N S

C

D A

B

R

b1

b2s1

s2

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N S

B

A

D

C

R

b1

b2s1

s2

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Classification of DC Generators

Separately excited generators

Self excited generators

Shunt generator

Seriesgenerator

Compound generator

Long shunt Short shunt

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Classification of DC Classification of DC Generators are classified asGenerators are classified as

(a) Separately excited d. c generators(a) Separately excited d. c generators

(b) self excited d.c generators(b) self excited d.c generators

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Classification of Self excited DC Classification of Self excited DC GeneratorsGenerators

Shunt generatorsShunt generators

Series generatorsSeries generators

Compound generatorsCompound generators

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Classification of Compound Classification of Compound generatorsgenerators

Long shunt compound generatorLong shunt compound generator

Short shunt compound generatorShort shunt compound generator

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Separately excited DC GeneratorsSeparately excited DC Generators

In this type, the field In this type, the field winding is excited by winding is excited by a separate source of a separate source of d.c currentd.c current

The field current can The field current can be varied by a be varied by a variable resistance variable resistance connected in series connected in series as shown in Fig.1as shown in Fig.1

Fig.1

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Shunt GeneratorShunt Generator

Field winding connected Field winding connected

in parallel to armaturein parallel to armature

• IIshsh = =

• Ia = Ish + I

• Eg = V + IaRa

sh

V

R

Z

ZZ

A

AA

V

+

-

Fig.1

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Series Generator

• Ia = Ise = I• Eg = V + IaRa + IsRse

Field winding is connected in series with armature

Fig.2

Eg V

+

-

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Long Shunt Compound Generator

Both series and shunt windings are present

• Ia = Ise = I

• Eg = V + IaRa + IseRse

• Ish = sh

V

R

Vsh

Rsh+

-

V

Fig.3

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Short Shunt Compound GeneratorShort Shunt Compound Generator

In this generator, In this generator, the shunt field is the shunt field is connected across connected across the armature the armature terminals only as terminals only as shown in Fig.5.shown in Fig.5.

Rsh

A

AA

Fig.5

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E.M.F Equation For Short Shunt E.M.F Equation For Short Shunt Dc Compound GeneratorDc Compound Generator

Generated EMF, E Generated EMF, E gg=V+I =V+I a a RRaa+I +I se se R R se se + Brush drop+ Brush drop

Rsh

A

AA