502942 class 36 dc generator
TRANSCRIPT
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Welcome to
Lectures on D.C.Machine
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D. C. Generator
http://upload.wikimedia.org/wikipedia/commons/a/a9/Prokudin-Gorskii-30.jpghttp://upload.wikimedia.org/wikipedia/commons/a/a9/Prokudin-Gorskii-30.jpghttp://upload.wikimedia.org/wikipedia/commons/a/a9/Prokudin-Gorskii-30.jpg -
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Portable D. C. Generator
http://upload.wikimedia.org/wikipedia/commons/7/7d/Portable_electrical_generator_angle.jpg -
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DIRECT CURRENT
MACHINESDC machine Construction
The major advantages of DCmachines are: easy speed andtorque regulation.
The stator of the DC motor haspoles, which are excited by DCcurrent to produce magnetic fields.
The rotor has a ring-shapedlaminated iron-core with slots.
Coils with several turns are placed inthe slots. The distance between thetwo legs of the coil is about 180electric degrees.
N S
Stator with
with polesBrush
Rotor
Field
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D. C. Generator
Principle of Operation
When a conductor rotates in a magnetic field,
dynamically induced e.m.f is produced in it
according to Faradays law of electromagnetic
induction
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Generated EMF
Let
Ei.epathsparalleltheofoneanyingeneratedEMFEEMFGenerated
ArmatureinpathparallelanyininducedEMFE
rpminrotationArmatureN
ArmatureinPathsParallelofNo.A
polesGeneratorofNo.P
SlotperConductorsofNo.SlotsofNo.
ConductorsArmatureofNo.TotalZ
WbinFlux/Pole
g =
====
===
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secN
60dt,revolution1forTime
N/60s/secRevolutionofNo.
WbPd,revolution1intorcut/conducFluxNow,
voltdt
dConductorGenerated/EMFAverage
=
==
=
Hence, according to Faradays Laws of electromagnetic induction,
volt60
PN
60/N
P
volt
dt
dconductorGenerated/EMF
==
=
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For Wave wound Generator
No. of Parallel Paths = 2
No. of Conductors (in series) in 1 path = Z/2
volt
120
ZPNvolt
260
PNpathGenerated/EMF ==
Z
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For Lap wound Generator
No. of Parallel Paths = P
No. of Conductors (in series) in 1 path = Z/P
volt60
ZNvolt
P60
PNpathGenerated/EMF ==
Z
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In General,
Generated EMF
windinglapforP
windingwavefor2Awhere,
volt
A
P
60
ZNEg
==
=
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Also,
voltA
P
Z
voltA
P
Z
N
Eg
=
= 2602
2
1
For a given D.C. Machine, Z, P and A are constants
Hence, Putting
rps)inis(N
voltsNk2kE
get,we,A
ZPk
aag
a
==
=
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Types of D.C. Generators
According to the way in which their fieldsare excited, generators are classified into :
i) Separately excited D.C. Generator
ii) Self- excited D.C. Generator
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Separately excited D.C. Generators are those whose field
magnets are energized from an independent source of D.C. Current
Eg
L
O
A
D
+
-
I
Field Winding
R
Brush
Brush
V
If
DropsBrushIREV ag =Ra = Armature Resistance
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Self excited D.C. Generators are those whose field
magnets are energized by the currents produced by the generators
themselves.
ere are 3 types of self-excited D.C. Generators named according to
e manner in which their field coils are connected to the armature.
ese are :
Shunt wound D.C. Generator
Series wound D.C. Generator
Compound wound D.C. Generator
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i) Shunt wound D.C. Generator
Eg
LOAD
+
-
I
Shunt Field V
Ia
Ish
Rsh
Ra
Rsh Shunt Field Resistance
Ra - Armature Resistance
sha III +=DropsBrushRIEV aag =
shshRIV =
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Eg
L
O
A
D
+
Ia=Ise=I
Se ries Field
V
Rse
ii) Series wound D.C. Generator
DropsBrush)RR(IEV seaag +=
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iii) Compound wound D.C. Generator
Eg
L
OA
D
I
Shunt Field
V
Ia
Ish
Series Field
Short Shunt
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Eg
L
O
AD
I
Shunt FieldV
Ia
Ish
Series Field
Long Shunt
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Ex.1 A D.C. Shunt Generator delivers 450A at 230V and the
resistance of the shunt field and armature are 50 and 0.03
respectively. Calculate the generated EMF.
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Ex.2 An 8 - pole D.C. Shunt Generator with 778 wave
wound armature conductors running at 500 rpm supplies
a load of 12.5 resistance at terminal voltage of 250V.
The armature resistance is 0.24 and the field resistance is 250 .
Find the armature current, the generated EMF and the flux per pole.