The document discusses DC generators and their operation. It begins by explaining that DC generators convert mechanical input power into electrical output power through rotation. It then describes the basic principles of operation, including Faraday's law of induction. It discusses the different types of DC generators - separately excited, series, shunt, and compound - and how their field windings are connected. Finally, it outlines some common applications of DC generators in areas like electroplating, battery charging, and supplying DC motors.

1. BE 8251– Basics of Electrical Engineering
Department of Electrical and Electronics Engineering
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2. DC generator
• These machines convert mechanical input power into DC
electrical output power in a rotating device, called a
generator.
PRINCIPLE OF OPERATION
• DC generator converts mechanical energy into electrical
energy. when a conductor move in a magnetic field in
such a way conductors cuts across a magnetic flux of
lines and emf produces in a generator and it is defined
by faradays law of electromagnetic induction emf causes
current to flow if the conductor circuit is closed.
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4. ⮚ If the shaft is rotated at constant rpm, the conductor
(glued to the surface of the cylinder) too will rotate at the
same speed. In the process of rotation, the conductor will
cut the lines of forces of stator magnetic field
⮚ According to Faraday’s law, emf (alternating) will be
induced in the armature conductors; As the conductor
moves, it sometimes cuts flux lines produced by N-pole
and some other time it cuts flux lines produced by the S-
pole.
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5. ⮚ The polarity of the induced voltage is therefore going to
change. The sense of induced emf will be ⊗ when the
conductor will be at position A (under the influence of
north pole) and it will ⨀ when the conductor will be at
position B (under the influence of the south pole).
⮚ This voltage can be made unidirectional by using
commutator segments and brushes.
⮚ Generated EMF
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6. TYPES OF D.C. GENERATORS
⮚ The magnetic field in a d.c. generator is normally
produced by electromagnets rather than permanent
magnets.
⮚ Generators are generally classified according to their
methods of field excitation.
⮚ On this basis, d.c. generators are divided into the
following two classes:
(i) Separately excited d.c. generators
(ii) Self-excited d.c. generators
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7. • (i)Separately Excited D.C. Generators
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8. ❖ A d.c. generator whose field magnet winding is supplied
from an independent external d.c. source (e.g., a battery
etc.) is called a separately excited generator.
❖ The voltage output depends upon the speed of rotation
of armature and the field current (Eg =fPØ ZN/60 A).
❖ The greater the speed and field current, greater is the
generated e.m.f.
❖ It may be noted that separately excited d.c. generators
are rarely used in practice.
❖ The d.c. generators are normally of self-excited type.
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9. Armature current, Ia = IL
Terminal voltage, V = Eg - IaRa
Electric power developed = EgIa
Power delivered to load = EgIa - Ia
2Ra
(ii)Self-Excited D.C. Generators
⮚ A d.c. generator whose field magnet winding is supplied
current from the output of the generator itself is called a
self-excited generator.
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10. There are three types of self-excited generators depending
upon the manner in which the field winding is connected
to the armature, namely;
(a)Series generator;
(b) Shunt generator;
(c) Compound generator
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11. (a) Series generator
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12. ⮚ In a series wound generator, the field winding is
connected in series with armature winding so that whole
armature current flows through the field winding as well
as the load.
⮚ Since the field winding carries the whole of load current,
it has a few turns of thick wire having low resistance.
⮚ Series generators are rarely used except for special
purposes e.g., as boosters.
• Armature current, Ia = Ise = IL = I(say)
• Terminal voltage, V = EG - I(Ra + Rse)
• Power developed in armature = EgIa
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13. • Power delivered to load
= EG Ia – Ia
2(Ra + Rse) = Ia (EG - I(Ra - Rse))= V Ia OR V IL
(b) Shunt generator
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14. ⮚ In a shunt generator, the field winding is connected in
parallel with the armature winding so that terminal
voltage of the generator is applied across it.
⮚ The shunt field winding has many turns of fine wire
having high resistance.
⮚ Therefore, only a part of armature current flows through
shunt field winding and the rest flows through the load.
Shunt field current, Ish = V/Rsh
Armature current, Ia = IL + Ish
Terminal voltage, V = Eg - IaRa
Power developed in armature = EgIa
Power delivered to load = VIL
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15. (c) Compound generator
⮚ In a compound-wound generator, there are two sets of
field windings on each pole—one is in series and the
other in parallel with the armature.
⮚ A compound wound generator may be: Short Shunt in
which only shunt field winding is in parallel with the
armature winding.
⮚ Long Shunt in which shunt field winding is in parallel
with both series field and armature winding
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18. • APPLICATIONS OF DC GENERATOR
• DC Separately Exited Generator:
• As a supply source to DC Motors, whose speed is to be
controlled for certain applications. Where a wide range
of voltage is required for the testing purposes.
• DC Shunt Generator
• The terminal voltage of DC shunt generator is more or
less constant from no load to full load .Therefore these
generators are used where constant voltage is required.
• For electro plating
• Battery charging
• For excitation of Alternators.
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19. DC Series Generator
The terminal voltage of series generator increases with
load current from no load to full load .Therefore these
generators are,
• Used as Boosters
• Used for supply to arc Lamps
DC Compound Generator:
• Differential Compound generators are used to supply dc
welding machines. Level compound generators are used
to supply power for offices, hostels and Lodges etc. Over
compound generators are used to compensate the
voltage drop in Feeders.
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