DC Generator.ppt

Basically a D.C. machine is an alternating current machine. The e.m.f. generated in the conductor is alternating in nature. With the help of the commutator segments this alternating e.m.f. is converted into a direct one.
The working of a DC generator is based on the principle that, when a conductor cuts a magnetic field, an e.m.f. is induced in the conductor.
A dynamically induced e.m.f. will be produced in the conductor when it will cut the magnetic flux as per the laws of electromagnetic induction

1. DC GENERATOR & DC
MOTORS
By
Dr. M. Ajay Kumar
Associate Professor, EEE.
1Basic Electrical Engineering

2. ADCgeneratorconvertsmechanicalenergy
intoelectricalenergy(DC).
TheworkingofaDCgeneratorisbasedon
theprinciplethat,whenaconductorcutsa
magneticfield,ane.m.f.isinducedinthe
conductor.
Adynamicallyinducede.m.f.willbe
producedintheconductorwhenitwillcut
themagneticfluxasperthelawsof
electromagneticinduction
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3. Ifthecircuitisclosedthisinducede.m.f.
willcauseacurrenttoflowthrough
circuit.
BasicallyaD.C.machineisanalternating
currentmachine.Thee.m.f.generatedin
theconductorisalternatinginnature.
Withthehelpofthecommutator
segmentsthisalternatinge.m.f.is
convertedintoadirectone.
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4. 4Basic Electrical Engineering

5. 1.Pole
2.Armature
3.Yoke
4.Commutator
5.Brushes
6.Interpole
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8. There are two types of windings
Lap winding
•A = P
•The armature
windings are
divided into
no. of sections
equal to the no
of poles
Wave winding
•A = 2
•Used in high
voltage low
current output.
•Requires 2
brushes
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11. Let, Ø= flux per pole in weber
Z = Total number of conductor
P = Number of poles
A = Number of parallel paths
N =armature speed in rpm
Eg = emf generated in any on of the
parallel path
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12. Flux cut by 1 conductor
in 1 revolution = P * φ
Flux cut by 1 conductor in
60 sec = P φ N /60
Avg emf generated in 1
conductor = PφN/60
Number of conductors in
each parallel path= Z /A
Eg = PφNZ/60A
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13. •Separately excited DC machine
•Self excited DC machine
Shunt wound DC generator
Series wound DC generator
Compound wound
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14. In this type of machine, the field of
the machine is excited by an
independent external source. This
source can be a battery, rectifier
circuit or a D.C. generator
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16. Vbe the field excitation voltage
R
fbe the field resistance.
I
fbe the field current
E
gbe the generated e.m.f.
in the armature
R
abe the armature resistance
I
abe the armature current
I
Lbe the load current
V
Lbe the load voltage
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17. In this type of
machine the
field winding is
connected in
series with the
armature
winding of a DC
generator
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18. Inthistypeofmachine,sincethe
fieldwindingcarrythefull
armaturecurrent,thefieldwinding
haslessnumberofturnsofwireof
largecrosssectionalarea.Fromthe
machinecircuitshown,
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19. Inthistypeof
machine,the
fieldwindingis
connectedin
parallelwiththe
armature
winding.
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20. 20Basic Electrical Engineering

21. InthistypeofDCmachinethepoles
arehavingtwoseparatewindings.
ThatisforacompoundwoundDC
machinetherearetwofieldwindings,
namely,theshuntfieldwindingand
theseriesfieldwinding.
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22. Dependinguponhowthesetwo
windingsareconnectedwiththe
armatureoftheDCmachine,theyare
classifiedas,
•LongshuntcompoundDCmachine.
•ShortshuntcompoundDCmachine.
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23. Long shunt Short shunt
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24. Thischaracteristiciscalledthe
magneticcharacteristicortheOpen
CircuitCharacteristic(O.C.C.)ofa
separatelyexcitedD.C.generator.
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25. •OpenCircuitCharacteristic
•Internalcharacteristic
•Theexternalcharacteristic
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26. ThevoltagebuildupinaDCgenerator
dependsonthepresenceofaresidualfluxin
thepolesofthegenerator.
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27. •Internalcharacteristic
•Externalcharacteristic
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28. •LineOArepresentthefieldresistance
•LineOBiscalledthecriticalfield
resistance.
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29. •DCshuntgeneratorisusedforsuch
applicationswhereconstantvoltageis
required.
•DCseriesgeneratorsareusedasBoosters
andalsoasasupplyforarclamps.
•DifferentialCompoundgeneratorsareused
tosupplydcweldingmachines.
•Levelcompoundgeneratorsareusedto
supplypowerforoffices,hostelsandLodges
etc.
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30. •Overcompoundgeneratorsareusedto
compensatethevoltagedropinFeeders.
•Separatelyexcitedgeneratorareused
asasupplyforDCMotors,itisalsoused
forsuchapplicationswhereawiderange
ofvoltageisrequiredforthetesting
purposes.
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