Electrical Machines and Energy Conversion

Name: Electrical Machines and Energy Conversion
Uploaded: 2017-09-08T14:52:38+00:00
Duration: PTM16S12
Channel: Annabella Kathleen Bruce
Description: Electrical Machines and Energy Conversion

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.
Copyright © 2006 by Sperika Enterprises and published by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

FIGURE 4-2 Voltage induced in the ac generator as a function of the angle of rotation.

FIGURE 4-3 Voltage induced as a function of time.

FIGURE Elementary dc generator is simply an ac generator equipped with a mechanical rectifier called a commutator. Copyright © 2006 by Sperika Enterprises and published by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

FIGURE 4-5 The elementary dc generator produces a pulsating dc voltage.

FIGURE 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. Copyright © 2006 by Sperika Enterprises and published by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

FIGURE 4-7 Schematic diagram of a dc generator having 4 coils and 4 commutator bars. See Fig. 4.9.

FIGURE 4-8 The voltage between the brushes is more uniform than in Fig

FIGURE The actual physical construction of the generator shown in Fig The armature has 4 slots, 4 coils, and 4 commutator bars. Copyright © 2006 by Sperika Enterprises and published by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

FIGURE 4-10 Position of the coils when the armature of Fig. 4
FIGURE Position of the coils when the armature of Fig. 4.9 has rotated through 45. Copyright © 2006 by Sperika Enterprises and published by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

FIGURE 4-14 Magnetic field produced by the current flowing in the armature conductors.

FIGURE 4-15 Armature reaction distorts the field produced by the N, S poles.

FIGURE 4-16 Commutating poles produce an mmfc that opposes the mmfa of the armature.

FIGURE 4-17 Separately excited 2-pole generator
FIGURE Separately excited 2-pole generator. The N, S field poles are created by the current flowing in the field windings. Copyright © 2006 by Sperika Enterprises and published by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

FIGURE 4-18a Flux per pole versus exciting current.

FIGURE 4-18b Saturation curve of a dc generator.

FIGURE 4-19 a. Self-excited shunt generator. b
FIGURE 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. Copyright © 2006 by Sperika Enterprises and published by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

FIGURE 4-20 Controlling the generator voltage with a field rheostat
FIGURE Controlling the generator voltage with a field rheostat. A rheostat is a resistor with an adjustable sliding contact. Copyright © 2006 by Sperika Enterprises and published by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

FIGURE 4-21 The no-load voltage depends upon the resistance of the shunt-field circuit.

FIGURE 4-22 Equivalent circuit of a dc generator.

FIGURE 4-23 Separately excited generator under load.

FIGURE 4-24 Load characteristic of a separately excited generator.

FIGURE 4-25 a. Compound generator under load. b. Schematic diagram.

FIGURE 4-26 Typical load characteristics of dc generators.

FIGURE 4-27 Cross section of a 2-pole generator.

FIGURE 4-28 Cutaway view of a 4-pole shunt generator
FIGURE Cutaway view of a 4-pole shunt generator. It has 3 brushes per brush set. Copyright © 2006 by Sperika Enterprises and published by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

FIGURE 4-29 Adjacent poles of multipole generators have opposite magnetic polarities.

FIGURE Armature of a dc generator showing the commutator, stacked laminations, slots, and shaft. (Courtesy of General Electric Company, USA) Copyright © 2006 by Sperika Enterprises and published by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

FIGURE 4-31 Armature laminations with tapered slots.

FIGURE 4-32 Crosssection of a slot containing 4 conductors.

FIGURE 4-33 Commutator of a dc machine.

FIGURE 4-34 a. Brushes of a 2-pole generator. b
FIGURE a. Brushes of a 2-pole generator. b. Brushes and connections of a 6-pole generator. Copyright © 2006 by Sperika Enterprises and published by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

FIGURE 4-35 a. Carbon brush and ultraflexible copper lead. b
FIGURE 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) Copyright © 2006 by Sperika Enterprises and published by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

FIGURE Sectional view of a 100 kW, 250 V, 1750 r/min 4-pole dc generator. (Courtesy of General Electric Company, USA) Copyright © 2006 by Sperika Enterprises and published by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

FIGURE 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 r/min Total weight 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. Copyright © 2006 by Sperika Enterprises and published by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

FIGURE 4-38a Schematic diagram of a 12-pole, 72-coil dc generator.

Electrical Machines and Energy Conversion
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Electrical Machines and Energy Conversion

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