patelrajalkumarhasmukhbhai2130904-170402095939.ppt

Educational ppt

1. DC Machine And Transformer(2130904)
Active Learning Assignment
on
Types of DC Generator
Prepared By:
Patel RajalKumar H.
Guided By :
Prof. Hitesh T. Mannai
Gandhinagar Institute of Technology
Electrical Department
Batch-B3

2. Types of
DC Generator
FieldExcitation
Sepretly Exited Self Exited
Series Generator Shunt Generator Compound Generator
Permanent
Magnet
2

3. Thesearethegeneratorswhosefieldmagnetsareenergizedby
some externaldc sourcesuchasBattery.
Separately Excited DC Generator
3
I
a=Armaturecurrent
I
L=Loadcurrent
V=Terminalvoltage
E
g=Generatedemf
Voltagedropinthearmature=I
a×R
a(R/sub>aisthe
armatureResistance)
Let,I
a=I
L=I(say)
Then,Voltageacrosstheload,V=IR
a
Powergenerated,P
g=E
g×I
Powerdeliveredtotheexternalload,P
L=V×I.

4. Thesearethegeneratorswhosefieldmagnetsareenergizedbythe
currentsuppliedbythemselves.
Inthesetypeofmachinesfieldcoilsareinternallyconnectedwiththe
armature.Duetoresidualmagnetismsomefluxisalwayspresentin
thepoles.
Whenthearmatureisrotatedsomeemfisinduced.Hencesome
inducedcurrentisproduced.Thissmallcurrentflowsthroughthefield
coilaswellastheloadandtherebystrengtheningthepoleflux.
Self Exited DC Generator
4

5. Asthepolefluxstrengthened,itwillproducemorearmatureemf,
whichcausefurtherincreaseofcurrentthroughthefield.This
increasedfieldcurrentfurtherraisesarmatureemfandthiscumulative
phenomenoncontinuesuntiltheexcitationreachestotheratedvalue.
5

6. AccordingToThePositionOfTheFieldCoilDC
GeneratorHasAThreeType
1)SeriesGenerator
2)ShuntGenerator
3)CompoundGenerator
6

7. Series Generator
Inthesetypeofgenerators,thefieldwindingsareconnectedinseries
witharmatureconductors.
So,wholecurrentflowsthroughthefieldcoilsaswellastheload.As
seriesfieldwindingcarriesfullloadcurrentitisdesignedwith
relativelyfewturnsofthickwire.
TheElectricalresistanceofseriesfieldwindingisthereforeverylow
(nearly0.5Ω).
7

8. 8
Let,
R
sc=Serieswindingresistance
I
sc=Currentflowingthroughtheseriesfield
R
a=ArmatureResistance
I
a=Armaturecurrent
I
L=Loadcurrent
V=Terminalvoltage
E
g=Generatedemf
Then,I
a=I
sc=I
L=I(say)
Voltageacrosstheload,V=E
g-I(I
a×R
a)
Powergenerated,P
g=E
g×I
Powerdeliveredtotheload,P
L=V×I

9. Shunt Generator
Inthesetypeofgenerators,thefieldwindingsareconnectedinParallelwith
armatureconductors.
Inshuntgeneratorsthevoltageinthefieldwindingissameasthevoltage
acrosstheterminal.
HerearmaturecurrentI
aisdividingintwoparts,oneisshuntfieldcurrentI
sh
andanotherisloadcurrentI
L.
So,I
a=I
sh+I
LTheeffectivepoweracrosstheloadwillbemaximumwhenI
L
willbemaximum.
So,itisrequiredtokeepshuntfieldcurrentassmallaspossible.Forthis
purposetheresistanceoftheshuntfieldwindinggenerallykepthigh(100Ω)
andlargenoofturnsareusedforthedesiredemf.
9

10. 10
Let,
R
sh=ShuntwindingResistance
I
sh=Currentflowingthroughtheshuntfield
R
a=ArmatureResistance
I
a=Armaturecurrent
I
L=Loadcurrent
V=Terminalvoltage
E
g=Generatedemf
Shunt field current, I
sh= V/R
sh
Voltage across the load, V = E
g-I
aR
a
Power generated, P
g= E
g ×I
a
Power delivered to the load, P
L= V×I
L

11. Compound DC Generator
Inserieswoundgenerators,theoutputvoltageisdirectly
proportionalwithloadcurrent.Inshuntwoundgenerators,output
voltageisinverselyproportionalwithloadcurrent.Acombinationof
thesetwotypesofgeneratorscanovercomethedisadvantagesofboth.
ThiscombinationofwindingsiscalledcompoundwoundDC
generator.
Compoundwoundgeneratorshavebothseriesfieldwindingand
shuntfieldwinding.
Onewindingisplacedinserieswiththearmatureandtheotheris
placedinparallelwiththearmature.11

12. Compound Generator Has A two Type
1)Short Shunt
2)Long shunt
12

13. The generators in which only shunt field winding is in parallel
with the armature winding as shown in figure.
Short Shunt DC compound Generator
13
Series field current, I
sc= I
L
Shunt field current,
I
sh= (V + I
scR
sc)/R
sh
Armature current, I
a= I
sh+ I
L
Voltage across the load,
V = E
g-I
aR
a-I
scR
sc
Power generated, P
g= E
g ×I
a
Power delivered to the load, P
L=V×I
L

14. Thegeneratorsinwhichshuntfieldwindingisinparallelwithboth
seriesfieldandarmaturewindingasshowninfigure.
Long Shunt Compound DC Generator
14
Shunt field current, I
sh=V/R
sh
Armature current, I
a= series field current,
I
sc= I
L + I
sh
Voltage across the load, V=E
g-I
aR
a-I
scR
sc
=E
g-I
a(R
a + R
sc)
[∴I
a= I
cs]
Power generated, P
g= E
g ×I
a
Power delivered to the load, P
L=V×I
L

15. Inacompoundgenerator,theshuntfieldisstrongerthanthe
seriesfield.Whentheseriesfieldassiststheshuntfield,
generatorissaidtobecommutativelycompoundgenerator.
Ontheotherhandifseriesfieldopposestheshuntfield,the
generatorissaidtobedifferentiallycompoundgenerator.
15

16. 16