Unit 29 DC Generators
Objectives:
• Discuss the operation of DC generators.
• List the factors that determine the amount
of output voltage produced by a generator.
• List the three major types of DC
generators.
Unit 29 DC Generators
Objectives:
• List different types of armature windings.
• Describe the differences between series
and shunt field windings.
• Discuss the operating differences between
various types of generators.
Unit 29 DC Generators
Objectives:
• Discuss schematic diagrams for different
types of DC generators.
• Show the brushes set to the neutral plane
position on the commutator of a DC
machine.
Unit 29 DC Generators
Construction
• A generator is a device that converts
mechanical energy into electrical energy.
• Direct-current generators operate on the
principle of magnetic induction.
• Loops of wire cut through magnetic flux
lines when the shaft is mechanically
turned.
Unit 29 DC Generators
Construction
• Brushes and sliprings are used to provide
a pathway for electrical connections to
external loads needing electrical power.
• The voltage produced in all rotating
armatures is alternating voltage.
• A commutator is used to allow DC power
generation.
Unit 29 DC Generators
Basic generator construction.
Unit 29 DC Generators
Cutaway graphic of a generator at 0 .
Unit 29 DC Generators
Cutaway graphic of a generator at 90 .
Unit 29 DC Generators
Cutaway graphic of a generator at 180 .
Unit 29 DC Generators
Cutaway graphic of a generator at 270 .
Unit 29 DC Generators
Cutaway graphic of a generator at 360 .
Unit 29 DC Generators
The commutator is used to convert the AC voltage
produced in the armature into DC voltage.
Unit 29 DC Generators
Commutator action at 0 .
Unit 29 DC Generators
Commutator action at 90 .
Unit 29 DC Generators
Commutator action at 180 .
Unit 29 DC Generators
Commutator action at 270 .
Unit 29 DC Generators
Commutator action at 360 .
Unit 29 DC Generators
Increasing the number of turns increases the
output voltage.
Unit 29 DC Generators
Increasing the number of loops produces a
smoother output voltage.
Unit 29 DC Generators
The loops of wire are wound around slots in a
metal core.
Unit 29 DC Generators
Construction
• The brushes ride against the commutator
segments and are used to connect the
armature to the external circuit of the DC
machine.
Unit 29 DC Generators
Construction
• Pole pieces located inside the housing
provide the magnetic field required for the
generator action.
Unit 29 DC Generators
Construction
• The pole pieces are electromagnets that
replace the permanent magnets in a
simple generator.
• A magneto is a DC generator that uses
permanent magnets as its field.
Unit 29 DC Generators
Construction
• Most DC machines use wound
electromagnets to provide the magnetic
field. There are two types of field windings:
series field windings and shunt field
windings.
Unit 29 DC Generators
Series and shunt field windings.
Unit 29 DC Generators
•
•
Construction
Simple schematics show the connections
of the armature to the series and shunt field
windings.
Generators fall into three main categories:
1. Series generators
2. Shunt generators
3. Compound generators
Unit 29 DC Generators
Series generator schematic.
Unit 29 DC Generators
Shunt field generator windings are connected
in parallel with the armature.
Unit 29 DC Generators
Long shunt generator schematic.
Unit 29 DC Generators
Short shunt generator schematic.
Unit 29 DC Generators
Review:
1. A generator is a machine that converts
mechanical energy into electrical energy.
2. Generators operate on the principle of
magnetic induction.
3. Alternating current is produced in all
rotating armatures.
Unit 29 DC Generators
Review:
4. The commutator changes the alternating
current produced in the armature into
direct current.
5. The brushes are used to make contact
with the commutator and to carry the
output current to the outside circuit.
Unit 29 DC Generators
Review:
6. The loops of wire, iron core, and
commutator are made as one unit and are
referred to as the armature.
7. The armature connection is marked A1
and A2.
8. Series field windings are made with a few
turns of large wire and have a very low
resistance.
Unit 29 DC Generators
Review:
9. Series field windings are connected in
series with the armature.
10. Series field windings are marked S1 and
S2.
11. Shunt field windings are connected in
series with the armature.
Unit 29 DC Generators
Review:
12. Shunt field windings are connected in
parallel with the armature.
13. The shunt field windings are marked F1
and F2.
14. Series generators increase their output
voltage as load is added.
Unit 29 DC Generators
Review:
15. Shunt generators decrease their output
voltage as load is added.
16. The voltage regulation of a DC generator
is proportional to the resistance of the
armature.
17. Compound generators contain both series
and shunt field windings.
Unit 29 DC Generators
Review:
18. A long shunt compound generator has the
shunt field connected in parallel with both
the armature and the series field.
19. A short shunt compound generator has
the shunt field connected in parallel with
the armature, but in series with the series
field.
Unit 29 DC Generators
Review:
20. Interpoles are small pole pieces
connected between the main field poles
and are used to help correct armature
reaction.
21. Interpoles are connected in series with the
armature.