Basic Electrical and Electronics Engineering: Unit II: Electrical Machines
EMF Induced in a DC Generator
with Solved Example Problems
Let Ɵ = Flux/pole in Weber,z = Total number of armature conductors = No of slots × No of conductors/slots,P = No of poles,A = No of parallel paths in armature.
EMF
INDUCED IN A DC GENERATOR
Let
Ɵ
= Flux/pole in Weber
z
= Total number of armature conductors
= No of slots ×No of conductors/slots
P
= No of poles
A
= No of parallel paths in armature
N
= Speed of rotation in revolutions per minute (rpm)
E
= EMF induced in any parallel path in armature.
Eg
= EMF generated in any one of the parallel paths (ie) E.
Average
emf generated/conductor = dϕ/dt ( n = 1)
Flux
cut/conductor in one revolution
dϕ
= ϕ P weber
No of revolutions/second = N/60
Time
for one revolution, dt = 60/ N second
According
to faraday's law of electromagnetic induction.
EMF
generated/conductor = dϕ/dt = ϕΡ/ (60/Ν)
ϕΡN/60
volt
For
a wave wound generator
No
fo parallel paths (A) = 2
No
of conductors in one path = Z/2
EMF
generated/path = 
For
a lap wound generator
No
of parallel paths (A) = P
No
of conductors in one path = Z/2 = Z/A
EMF
generated/path = 
Example: 1
A 4 pole, wave wound generator has
40 slots and 10 conductors are placed per slot. Find the generated emf when the
generator is driven at 1200 rpm and ϕ = 0.02 wb.
Given data
No
of poles P = 4
Total
number of conductors Z = No of slots > conductors/slot.
Z
= 40 × 10 = 400
Flux/pole
ϕ = 0.02 wb
Speed
N = 1200 rpm
Solution:
Generated
emf Eg = ϕPNZ / 60 A
For
a wave wound A = 2
Eg
= 0.02 x 400 x 4 × 1200 / 60 × 2
=
320 V
Example: 2
A 6 pole, Lap wound armature
rotated at 350 rpm is required to generate 300V. the useful flux per pole is
0.05 ωb. If the armature has 120 slots, calculate the number of conductors per
slot.
Given data
No
of poles, P = 6
Speed,
N = 350 rpm
Generated
emf, Eg = 300 V
No
of slots = 120
Flux/pole,
ϕ = 0.05 ωb
For
lap wound generator, A = P=6
To find
No
of conductors/slot.
Solution:
Generated
emf, Eg = 
No
of conductors Z = 
No
of conductors/slot =
Conductors/slot
= 9
Basic Electrical and Electronics Engineering: Unit II: Electrical Machines : Tag: : with Solved Example Problems - EMF Induced in a DC Generator
Basic Electrical and Electronics Engineering: Unit II: Electrical Machines
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