Dc generator
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EE-303.1EE-303.1 11
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
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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
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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
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EE-303.6EE-303.6 1515Pole Shoe
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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
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