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 07458 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. Copyright © 2006 by Sperika Enterprises and published by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

FIGURE 4-3 Voltage induced as a function of time. Copyright © 2006 by Sperika Enterprises and published by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

FIGURE 4-4 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 07458 All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

FIGURE 4-5 The elementary dc generator produces a pulsating dc voltage. Copyright © 2006 by Sperika Enterprises and published by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

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. Copyright © 2006 by Sperika Enterprises and published by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 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. Copyright © 2006 by Sperika Enterprises and published by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

FIGURE 4-8 The voltage between the brushes is more uniform than in Fig Copyright © 2006 by Sperika Enterprises and published by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

FIGURE 4-9 The actual physical construction of the generator shown in Fig. 4.7. 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 07458 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 4-10 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 07458 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. Copyright © 2006 by Sperika Enterprises and published by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

FIGURE 4-15 Armature reaction distorts the field produced by the N, S poles. Copyright © 2006 by Sperika Enterprises and published by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

FIGURE 4-16 Commutating poles produce an mmfc that opposes the mmfa of the armature. Copyright © 2006 by Sperika Enterprises and published by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

FIGURE 4-17 Separately excited 2-pole generator FIGURE 4-17 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 07458 All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

FIGURE 4-18a Flux per pole versus exciting current. Copyright © 2006 by Sperika Enterprises and published by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

FIGURE 4-18b Saturation curve of a dc generator. Copyright © 2006 by Sperika Enterprises and published by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

FIGURE 4-19 a. Self-excited shunt generator. b 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. Copyright © 2006 by Sperika Enterprises and published by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

FIGURE 4-20 Controlling the generator voltage with a field rheostat FIGURE 4-20 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 07458 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. Copyright © 2006 by Sperika Enterprises and published by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

FIGURE 4-22 Equivalent circuit of a dc generator. Copyright © 2006 by Sperika Enterprises and published by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

FIGURE 4-23 Separately excited generator under load. Copyright © 2006 by Sperika Enterprises and published by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

FIGURE 4-24 Load characteristic of a separately excited generator. Copyright © 2006 by Sperika Enterprises and published by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

FIGURE 4-25 a. Compound generator under load. b. Schematic diagram. Copyright © 2006 by Sperika Enterprises and published by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

FIGURE 4-26 Typical load characteristics of dc generators. Copyright © 2006 by Sperika Enterprises and published by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

FIGURE 4-27 Cross section of a 2-pole generator. Copyright © 2006 by Sperika Enterprises and published by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

FIGURE 4-28 Cutaway view of a 4-pole shunt generator FIGURE 4-28 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 07458 All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

FIGURE 4-29 Adjacent poles of multipole generators have opposite magnetic polarities. Copyright © 2006 by Sperika Enterprises and published by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

FIGURE 4-30 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 07458 All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

FIGURE 4-31 Armature laminations with tapered slots. Copyright © 2006 by Sperika Enterprises and published by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

FIGURE 4-32 Crosssection of a slot containing 4 conductors. Copyright © 2006 by Sperika Enterprises and published by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

FIGURE 4-33 Commutator of a dc machine. Copyright © 2006 by Sperika Enterprises and published by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

FIGURE 4-34 a. Brushes of a 2-pole generator. b FIGURE 4-34 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 07458 All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

FIGURE 4-35 a. Carbon brush and ultraflexible copper lead. b 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) Copyright © 2006 by Sperika Enterprises and published by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

FIGURE 4-36 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 07458 All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

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. Copyright © 2006 by Sperika Enterprises and published by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 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. Copyright © 2006 by Sperika Enterprises and published by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Theodore Wildi Electrical Machines, Drives, and Power Systems, 6e

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