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Electrical
Machines and
Energy
Conversion
Unit 1 Deck 2
DC Generator Basics
FIGURE 4-1
Schematic diagram of an elementary ac generator turning at 1 revolution per second.
Theodore Wildi
Electrical Machines, Drives, and Power
Systems, 6e
Copyright © 2006 by Sperika Enterprises and
published by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
FIGURE 4-2
Voltage induced in the ac generator as a function of the angle of rotation.
Theodore Wildi
Electrical Machines, Drives, and Power
Systems, 6e
Copyright © 2006 by Sperika Enterprises and
published by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
FIGURE 4-3
Voltage induced as a function of time.
Theodore Wildi
Electrical Machines, Drives, and Power
Systems, 6e
Copyright © 2006 by Sperika Enterprises and
published by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
FIGURE 4-4
Elementary dc generator is simply an ac generator equipped with a mechanical rectifier called a commutator.
Theodore Wildi
Electrical Machines, Drives, and Power
Systems, 6e
Copyright © 2006 by Sperika Enterprises and
published by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
FIGURE 4-5
The elementary dc generator produces a pulsating dc voltage.
Theodore Wildi
Electrical Machines, Drives, and Power
Systems, 6e
Copyright © 2006 by Sperika Enterprises and
published by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
FIGURE 4-6 The three armatures (a), (b), and (c) have identical windings. Depending upon how they are connected (to slip rings or a
commutator), an ac or dc voltage is obtained.
Theodore Wildi
Electrical Machines, Drives, and Power
Systems, 6e
Copyright © 2006 by Sperika Enterprises and
published by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
FIGURE 4-7
Schematic diagram of a dc generator having 4 coils and 4 commutator bars. See Fig. 4.9.
Theodore Wildi
Electrical Machines, Drives, and Power
Systems, 6e
Copyright © 2006 by Sperika Enterprises and
published by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
FIGURE 4-8
The voltage between the brushes is more uniform than in Fig. 4.5.
Theodore Wildi
Electrical Machines, Drives, and Power
Systems, 6e
Copyright © 2006 by Sperika Enterprises and
published by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
FIGURE 4-9
bars.
The actual physical construction of the generator shown in Fig. 4.7. The armature has 4 slots, 4 coils, and 4 commutator
Theodore Wildi
Electrical Machines, Drives, and Power
Systems, 6e
Copyright © 2006 by Sperika Enterprises and
published by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
FIGURE 4-10 Position of the coils when the armature of Fig. 4.9 has rotated through 45.
Theodore Wildi
Electrical Machines, Drives, and Power
Systems, 6e
Copyright © 2006 by Sperika Enterprises and
published by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
FIGURE 4-14 Magnetic field produced by the current flowing in the armature conductors.
Theodore Wildi
Electrical Machines, Drives, and Power
Systems, 6e
Copyright © 2006 by Sperika Enterprises and
published by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
FIGURE 4-15 Armature reaction distorts the field produced by the N, S poles.
Theodore Wildi
Electrical Machines, Drives, and Power
Systems, 6e
Copyright © 2006 by Sperika Enterprises and
published by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
FIGURE 4-16 Commutating poles produce an mmfc that opposes the mmfa of the armature.
Theodore Wildi
Electrical Machines, Drives, and Power
Systems, 6e
Copyright © 2006 by Sperika Enterprises and
published by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
FIGURE 4-17 Separately excited 2-pole generator. The N, S field poles are created by the current flowing in the field windings.
Theodore Wildi
Electrical Machines, Drives, and Power
Systems, 6e
Copyright © 2006 by Sperika Enterprises and
published by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
FIGURE 4-18a Flux per pole versus exciting current.
Theodore Wildi
Electrical Machines, Drives, and Power
Systems, 6e
Copyright © 2006 by Sperika Enterprises and
published by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
FIGURE 4-18b Saturation curve of a dc generator.
Theodore Wildi
Electrical Machines, Drives, and Power
Systems, 6e
Copyright © 2006 by Sperika Enterprises and
published by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
FIGURE 4-19 a. Self-excited shunt generator. b. Schematic diagram of a shunt generator. A shunt field is one designed to be connected
in shunt (alternate term for parallel) with the armature winding.
Theodore Wildi
Electrical Machines, Drives, and Power
Systems, 6e
Copyright © 2006 by Sperika Enterprises and
published by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
FIGURE 4-20 Controlling the generator voltage with a field rheostat. A rheostat is a resistor with an adjustable sliding contact.
Theodore Wildi
Electrical Machines, Drives, and Power
Systems, 6e
Copyright © 2006 by Sperika Enterprises and
published by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
FIGURE 4-21 The no-load voltage depends upon the resistance of the shunt-field circuit.
Theodore Wildi
Electrical Machines, Drives, and Power
Systems, 6e
Copyright © 2006 by Sperika Enterprises and
published by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
FIGURE 4-22 Equivalent circuit of a dc generator.
Theodore Wildi
Electrical Machines, Drives, and Power
Systems, 6e
Copyright © 2006 by Sperika Enterprises and
published by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
FIGURE 4-23 Separately excited generator under load.
Theodore Wildi
Electrical Machines, Drives, and Power
Systems, 6e
Copyright © 2006 by Sperika Enterprises and
published by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
FIGURE 4-24 Load characteristic of a separately excited generator.
Theodore Wildi
Electrical Machines, Drives, and Power
Systems, 6e
Copyright © 2006 by Sperika Enterprises and
published by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
FIGURE 4-25 a. Compound generator under load. b. Schematic diagram.
Theodore Wildi
Electrical Machines, Drives, and Power
Systems, 6e
Copyright © 2006 by Sperika Enterprises and
published by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
FIGURE 4-26 Typical load characteristics of dc generators.
Theodore Wildi
Electrical Machines, Drives, and Power
Systems, 6e
Copyright © 2006 by Sperika Enterprises and
published by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
FIGURE 4-27 Cross section of a 2-pole generator.
Theodore Wildi
Electrical Machines, Drives, and Power
Systems, 6e
Copyright © 2006 by Sperika Enterprises and
published by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
FIGURE 4-28 Cutaway view of a 4-pole shunt generator. It has 3 brushes per brush set.
Theodore Wildi
Electrical Machines, Drives, and Power
Systems, 6e
Copyright © 2006 by Sperika Enterprises and
published by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
FIGURE 4-29 Adjacent poles of multipole generators have opposite magnetic polarities.
Theodore Wildi
Electrical Machines, Drives, and Power
Systems, 6e
Copyright © 2006 by Sperika Enterprises and
published by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
FIGURE 4-30 Armature of a dc generator showing the commutator, stacked laminations, slots, and shaft. (Courtesy of General Electric
Company, USA)
Theodore Wildi
Electrical Machines, Drives, and Power
Systems, 6e
Copyright © 2006 by Sperika Enterprises and
published by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
FIGURE 4-31 Armature laminations with tapered slots.
Theodore Wildi
Electrical Machines, Drives, and Power
Systems, 6e
Copyright © 2006 by Sperika Enterprises and
published by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
FIGURE 4-32 Crosssection of a slot containing 4 conductors.
Theodore Wildi
Electrical Machines, Drives, and Power
Systems, 6e
Copyright © 2006 by Sperika Enterprises and
published by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
FIGURE 4-33 Commutator of a dc machine.
Theodore Wildi
Electrical Machines, Drives, and Power
Systems, 6e
Copyright © 2006 by Sperika Enterprises and
published by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
FIGURE 4-34 a. Brushes of a 2-pole generator. b. Brushes and connections of a 6-pole generator.
Theodore Wildi
Electrical Machines, Drives, and Power
Systems, 6e
Copyright © 2006 by Sperika Enterprises and
published by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
FIGURE 4-35 a. Carbon brush and ultraflexible copper lead. b. Brush holder and spring to exert pressure. c. Brush set composed of two
brushes, mounted on rocker arm. (Courtesy of General Electric Company, USA)
Theodore Wildi
Electrical Machines, Drives, and Power
Systems, 6e
Copyright © 2006 by Sperika Enterprises and
published by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
FIGURE 4-36 Sectional view of a 100 kW, 250 V, 1750 r/min 4-pole dc generator. (Courtesy of General Electric Company, USA)
Theodore Wildi
Electrical Machines, Drives, and Power
Systems, 6e
Copyright © 2006 by Sperika Enterprises and
published by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
FIGURE 4-37 This direct-current Thompson generator was first installed in 1889 to light the streets of Montreal. It delivered a current
of 250 A at a voltage of 110 V. Other properties of this pioneering machine include the following:
Speed
1300 r/min
Total weight
2390 kg
Armature diameter
292 mm
Stator internal diameter
330 mm
Number of commutator bars
76
Armature conductor size
#4
Shunt field conductor size
# 14
A modern generator having the same power and speed weighs 7 times less and occupies only 1/3 the floor space.
Theodore Wildi
Electrical Machines, Drives, and Power
Systems, 6e
Copyright © 2006 by Sperika Enterprises and
published by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
FIGURE 4-38a Schematic diagram of a 12-pole, 72-coil dc generator.
Theodore Wildi
Electrical Machines, Drives, and Power
Systems, 6e
Copyright © 2006 by Sperika Enterprises and
published by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
End of
Presentation
Electrical Machines and
Energy Conversion