# Class 12 DCGenerator

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```					                  Welcome to

Lectures on D.C.Machine

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D. C. Generator

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Portable D. C. Generator

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DIRECT CURRENT
MACHINES
DC machine Construction
•   The major advantages of DC
machines are: easy speed and                  Field
torque regulation.                                        Rotor
•   The stator of the DC motor has
poles, which are excited by DC
current to produce magnetic fields.
•   The rotor has a ring-shaped              N            S
laminated iron-core with slots.
•   Coils with several turns are placed in
the slots. The distance between the
two legs of the coil is about 180
Stator with
electric degrees.
Brush          with poles

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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 Faraday’s law of electromagnetic
induction

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Generated EMF

Let
φ  Flux/Pole in Wb
Z  Total No. of Armature Conductors
 No. of Slots  No. of Conductors per Slot
P  No. of Generator poles
A  No. of Parallel Paths in Armature
N  Armature rotation in rpm
E  EMF induced in any parallel path in Armature

Generated EMF E g  EMF generated in any one of the parallel paths i.e E

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dφ
Average EMF Generated/Conductor       volt
dt
Now, Flux cut/conduc in 1 revolution, dφ  φP Wb
tor
No. of Revolutions/sec  N/60
60
 Time for 1 revolution, dt     sec
N
Hence, according to Faraday’s Laws of electromagnetic induction,

dφ
EMF Generated/conductor      volt
dt
φP    φPN
            volt
60/N    60

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For Wave wound Generator

No. of Parallel Paths = 2

No. of Conductors (in series) in 1 path = Z/2

φPN Z        φZPN
EMF Generated/path       volt       volt
60  2        120

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For Lap wound Generator

No. of Parallel Paths = P

No. of Conductors (in series) in 1 path = Z/P

φPN Z        φZN
EMF Generated/path       volt      volt
60  P        60

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In General,

Generated EMF

φZN  P 
Eg         volt
60  A 
where, A  2 for wave winding
 P for lap winding

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Also,
1  2πN   P         ωφZ  P 
Eg          φZ   volt        volt
2π  60   A           2π  A 
For a given D.C. Machine, Z, P and A are constants

Hence, Putting
ZP
ka       , we get,
A
ωφ
Eg  ka        k a φN volts
2π
(N is in rps)

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