Cambridge University Press 978-1-108-43106-4 — Electrical Machines S. K. Sahdev Frontmatter More Information Electrical Machines Electrical machines convert energy existing in one form to another, usable, form. These machines can broadly be divided into three categories: generators, motors and transformers. Generators convert mechanical energy into electrical energy, motors convert electrical energy to mechanical energy, and transformers change the voltage level in ac system and are considered to be the backbone of a power system. Electrical machines play an important role in domestic appliances, commercial devices and industrial applications. It is important for students of electrical and electronics engineering to learn the basic concepts of transformers, motors, generators and magnetic circuits. This book explains the design of transformers, decoding of generators and performance of electrical motors through descriptive illustrations, solved examples and mathematical derivations. Construction, working principles and applications of various electrical machines are discussed in detail. In addition, it offers an engrossing discussion on special purpose machines, which is useful from an industrial prospective in building customised machines. The text contains hundreds of worked examples and illustrations and more than a thousand self-assessment exercises. It is an ideal textbook for undergraduate students of electrical and electronics engineering. S. K. Sahdev is Associate Dean at the Faculty of Technology and Science at Lovely Professional University, Jalandhar. He has more than thirty-five years of teaching experience. In addition, he has helped industrial units to set-up electrical laboratories for testing and developing their products. He has authored six books. His areas of interest include electrical machines, electric drives, power electronics and power systems. © in this web service Cambridge University Press www.cambridge.org Cambridge University Press 978-1-108-43106-4 — Electrical Machines S. K. Sahdev Frontmatter More Information Electrical Machines S. K. Sahdev © in this web service Cambridge University Press www.cambridge.org Cambridge University Press 978-1-108-43106-4 — Electrical Machines S. K. Sahdev Frontmatter More Information University Printing House, Cambridge CB2 8BS, United Kingdom One Liberty Plaza, 20th Floor, New York, NY 10006, USA 477 Williamstown Road, Port Melbourne, vic 3207, Australia 314 to 321, 3rd Floor, Plot No.3, Splendor Forum, Jasola District Centre, New Delhi 110025, India 79 Anson Road, #06–04/06, Singapore 079906 Cambridge University Press is part of the University of Cambridge. It furthers the University’s mission by disseminating knowledge in the pursuit of education, learning and research at the highest international levels of excellence. www.cambridge.org Information on this title: www.cambridge.org/9781108431064 © Cambridge University Press 2018 This publication is in copyright. Subject to statutory exception and to the provisions of relevant collective licensing agreements, no reproduction of any part may take place without the written permission of Cambridge University Press. First published 2018 Printed in India A catalogue record for this publication is available from the British Library ISBN 978-1-108-43106-4 Paperback Additional resources for this publication at www.cambridge.org/9781108431064 Cambridge University Press has no responsibility for the persistence or accuracy of URLs for external or third-party internet websites referred to in this publication, and does not guarantee that any content on such websites is, or will remain, accurate or appropriate. © in this web service Cambridge University Press www.cambridge.org Cambridge University Press 978-1-108-43106-4 — Electrical Machines S. K. Sahdev Frontmatter More Information This book is dedicated to my Parents, wife – Ritu Sahdev, son – Rohit Sahdev, daughter-in-law – Robina Sahdev and grandsons – Arnav and Adhiraj © in this web service Cambridge University Press www.cambridge.org Cambridge University Press 978-1-108-43106-4 — Electrical Machines S. K. Sahdev Frontmatter More Information Contents Preface Acknowledgements 1. Electro Magnetic Circuits Introduction 1.1 Magnetic Field and its Significance 1.2 Magnetic Circuit and its Analysis 1.3 Important Terms 1.4 Comparison between Magnetic and Electric Circuits 1.5 Ampere-turns Calculations 1.6 Series Magnetic Circuits 1.7 Parallel Magnetic Circuits 1.8 Leakage Flux 1.9 Magnetisation or B-H Curve 1.10 Magnetic Hysteresis 1.11 Hysteresis Loss 1.12 Importance of Hysteresis Loop Section Practice Problems 1.13 Electro Magnetic Induction 1.14 Faraday’s Laws of Electromagnetic Induction 1.15 Direction of Induced emf 1.16 Induced emf 1.17 Dynamically Induced emf 1.18 Statically Induced emf 1.19 Self Inductance 1.20 Mutual Inductance 1.21 Co-efficient of Coupling 1.22 Inductances in Series and Parallel 1.23 Energy Stored in a Magnetic Field 1.24 AC Excitation in Magnetic Circuits 1.25 Eddy Current Loss Section Practice Problems © in this web service Cambridge University Press xxi xxiii 1 1 2 3 3 5 6 6 7 8 21 22 23 24 24 28 29 30 31 31 33 34 34 35 36 41 42 44 46 www.cambridge.org Cambridge University Press 978-1-108-43106-4 — Electrical Machines S. K. Sahdev Frontmatter More Information viii Contents 1.26 Electro-mechanical Energy Conversion Devices 1.27 Torque Development by the Alignment of Two Fields 1.27.1 Soft Iron Piece Placed in the Magnetic Field 1.27.2 Permanent Magnet Placed in the Magnetic Field 1.27.3 Electromagnet Placed in the Magnetic Field 1.28 Production of Torque 1.28.1 In Case of Permanent Magnet 1.28.2 In Case of Electromagnet 1.29 Production of Unidirectional Torque 1.29.1 By Rotating the Main Magnets 1.29.2 By Changing the Direction of Flow of Current in the Conductors of Electromagnet 1.30 emf Induced in a Rotating Coil Placed in a Magnetic Field 1.31 Elementary Concept of Electrical Machines 1.31.1 Operation of Machine as a Generator (Conversion of Mechanical Energy into Electric Energy) 1.31.2 Operation of Machine as a Motor Section Practice Problems Review Questions Multiple Choice Questions 48 49 49 51 53 54 55 55 57 58 2. Single-Phase Transformers Introduction 2.1 Transformer 2.2 Working Principle of a Transformer 2.3 Construction of Transformer 2.3.1 Core Material 2.3.2 Core Construction 2.3.3 Transformer Winding 2.3.4 Insulation 2.3.5 Bushings 2.3.6 Transformer Tank 2.4 Simple Construction of Single-phase Small Rating (SAY 2 kVA) Transformers 2.5 An Ideal Transformer 2.6 Transformer on DC 2.7 emf Equation Section Practice Problems 2.8 Transformer on No-load 2.9 Effect of Magnetisation on No-load (Exciting) Current 2.10 Inrush of Magnetising Current Section Practice Problems 2.11 Transformer on Load 2.12 Phasor Diagram of a Loaded Transformer 2.13 Transformer with Winding Resistance 79 80 80 82 82 83 83 85 88 89 90 91 94 95 96 100 103 104 106 113 114 115 118 © in this web service Cambridge University Press 58 63 68 68 70 74 74 76 www.cambridge.org Cambridge University Press 978-1-108-43106-4 — Electrical Machines S. K. Sahdev Frontmatter More Information Contents 2.14 Mutual and Leakage Fluxes 2.15 Equivalent Reactance Section Practice Problems 2.16 Actual Transformer 2.17 Simplified Equivalent Circuit 2.18 Short Circuited Secondary of Transformer 2.19 Expression for No-load Secondary Voltage 2.20 Voltage Regulation 2.21 Approximate Expression for Voltage Regulation 2.22 Kapp Regulation Diagram Section Practice Problems 2.23 Losses in a Transformer 2.24 Effects of Voltage and Frequency Variations on Iron Losses 2.25 Efficiency of a Transformer 2.26 Condition for Maximum Efficiency 2.27 Efficiency vs Load 2.28 Efficiency vs Power Factor 2.29 All-day Efficiency Section Practice Problems 2.30 Transformer Tests 2.31 Polarity Test 2.32 Voltage Ratio Test 2.33 Open-circuit or No-load Test 2.34 Separation of Hysteresis and Eddy Current Losses 2.35 Short Circuit Test 2.36 Back-to-back Test Section Practice Problems 2.37 Classification of Transformers 2.38 Parallel Operation of Transformers 2.39 Necessity of Parallel Operation 2.40 Conditions for Parallel Operation of One-phase Transformers 2.41 Load Sharing between Two Transformers Connected in Parallel Section Practice Problems 2.42 Auto-transformer 2.43 Auto-transformer vs Potential Divider 2.44 Saving of Copper in an Auto-transformer 2.45 Advantages of Auto-transformer over Two-winding Transformer 2.46 Disadvantages of Auto-transformers 2.47 Phasor Diagram of an Auto-transformer 2.48 Equivalent Circuit of an Auto-transformer 2.49 Simplified Equivalent Circuit of an Auto-transformer 2.50 Conversion of a Two-winding Transformer to an Auto-transformer 2.51 Comparison of Characteristics of Auto-transformers and Two-winding Transformers © in this web service Cambridge University Press ix 119 119 122 123 125 127 128 129 130 131 140 142 143 145 146 152 152 154 156 158 158 159 159 161 165 167 179 181 181 182 182 184 194 195 199 199 200 200 201 203 203 205 207 www.cambridge.org Cambridge University Press 978-1-108-43106-4 — Electrical Machines S. K. Sahdev Frontmatter More Information x Contents 2.52 Applications of Auto-transformers Section Practice Problems Review Questions Multiple Choice Questions 3. Three-Phase Transformers Introduction 3.1 Merits of Three-phase Transformer over Bank of Three Single-phase Transformers 3.2 Construction of Three-phase Transformers 3.3 Determination of Relative Primary and Secondary Windings in Case of Three-phase Transformer 3.4 Polarity of Transformer Windings 3.5 Phasor Representation of Alternating Quantities in Three-phase Transformer Connections 3.6 Three-phase Transformer Connections 3.7 Selection of Transformer Connections 3.7.1 Star-Star (Yy0 or Yy6) Connections 3.7.2 Delta-Delta (Dd0 or Dd6) Connections 3.7.3 Star-Delta (Yd1 or Yd11) Connections 3.7.4 Delta-Star (Dy1 or Dy11) Connections 3.7.5 Delta-Zigzag Connections Section Practice Problems 3.8 Parallel Operation of Three-phase Transformers 3.9 Necessity of Parallel Operation of Three-phase Transformers 3.10 Conditions for Parallel Operation of Three-phase Transformers 3.11 Load Sharing between Three-phase Transformers Connected in Parallel 3.12 Three Winding Transformers (Tertiary Winding) 3.12.1 Stabilisation Provided by Tertiary Winding in Star-Star Transformer 3.13 Tap-changers on Transformers 3.14 Types of Tap-changers 3.14.1 No-load (or Off-load) Tap-changer 3.14.2 On-load Tap-changer Section Practice Problems 3.15 Transformation of Three-phase Power with Two Single-phase Transformers 3.16 Open-Delta or V-V Connections 3.17 Comparison of Delta and Open Delta Connections 3.18 T-T Connections or Scott Connections 3.19 Conversion of Three-phase to Two-phase and vice-versa 3.20 Difference between Power and Distribution Transformers 3.21 Cooling of Transformers 3.22 Methods of Transformer Cooling 3.23 Power Transformer and its Auxiliaries © in this web service Cambridge University Press 208 218 220 221 224 224 225 225 227 227 228 229 233 233 236 238 239 241 251 252 253 254 255 257 260 265 266 266 267 268 270 270 274 275 277 291 291 292 294 www.cambridge.org Cambridge University Press 978-1-108-43106-4 — Electrical Machines S. K. Sahdev Frontmatter More Information Contents 3.24 Maintenance Schedule of a Transformer 3.25 Trouble Shooting of a Transformer Section Practice Problems Review Questions Multiple Choice Questions 296 297 297 299 300 4. DC Generator Introduction 4.1 DC Generator 4.2 Main Constructional Features 4.3 Simple Loop Generator and Function of Commutator 4.4 Connections of Armature Coils with Commutator Segments and Location of Brushes 4.5 Armature Winding 4.6 Types of Armature Winding 4.7 Drum Winding 4.8 Lap Winding 4.9 Numbering of Coils and Commutator Segments in Developed Winding Diagram 4.10 Characteristics of a Simplex Lap Winding 4.11 Characteristics of a Multiplex Lap Winding 4.12 Equalising Connections and their Necessity 4.13 Simplex Wave Winding 4.14 Dummy Coils 4.15 Applications of Lap and Wave Windings Section Practice Problems 4.16 emf Equation 4.17 Torque Equation 4.18 Armature Reaction 4.19 Calculations for Armature Ampere-turns 4.20 Commutation 4.21 Cause of Delay in the Reversal of Current in the Coil going through Commutation and its Effect 4.22 Magnitude of Reactance Voltage 4.23 Good Commutation and Poor Commutation 4.24 Interpoles and their Necessity 4.25 Compensating Winding and its Necessity 4.26 Methods of Improving Commutation Section Practice Problems 4.27 Types of DC Generators 4.28 Separately-excited DC Generators 4.29 Self-excited DC Generators 4.30 Voltage Regulation of a DC Shunt Generator 4.31 Characteristics of DC Generators © in this web service Cambridge University Press xi 301 301 302 303 307 309 311 314 315 316 318 323 327 327 330 332 338 338 340 341 349 351 355 357 358 360 361 362 365 366 368 368 369 371 376 www.cambridge.org Cambridge University Press 978-1-108-43106-4 — Electrical Machines S. K. Sahdev Frontmatter More Information xii Contents 4.32 No-load Characteristics of DC Generators or Magnetisation Curve of DC Generator 4.33 Voltage Build-up in Shunt Generators 4.34 Critical Field Resistance of a DC Shunt Generator 4.35 Load Characteristics of Shunt Generator 4.36 Load Characteristics of Series Generators 4.37 Load Characteristics of Compound Generator 4.38 Causes of Failure to Build-up Voltage in a Generator 4.39 Applications of DC Generators 4.40 Losses in a DC Generator 4.41 Constant and Variable Losses 4.42 Stray Losses 4.43 Power Flow Diagram 4.44 Efficiency of a DC Generator 4.45 Condition for Maximum Efficiency Section Practice Problems Review Questions Multiple Choice Questions 5. DC Motors Introduction 5.1 DC Motor 5.2 Working Principle of DC Motors 5.3 Back emf 5.4 Electro-magnetic Torque Developed in DC Motor 5.5 Shaft Torque 5.6 Comparison of Generator and Motor Action 5.7 Types of DC Motors 5.8 Characteristics of DC Motors 5.9 Characteristics of Shunt Motors 5.10 Characteristics of Series Motors 5.11 Characteristics of Compound Motors 5.12 Applications and Selection of DC Motors 5.12.1 Applications of DC Motors 5.12.2 Selection of DC Motors 5.13 Starting of DC Motors 5.14 Necessity of Starter for a DC Motor 5.15 Starters for DC Shunt and Compound Wound Motors 5.16 Three-point Shunt Motor Starter 5.17 Four-point Starter 5.18 Calculation of Step Resistances Used in Shunt Motor Starter 5.19 Series Motor Starter Section Practice Problems © in this web service Cambridge University Press 376 377 378 379 380 380 381 381 382 383 384 384 384 385 387 390 392 395 395 396 396 397 398 399 399 401 405 405 407 408 409 409 410 411 411 412 412 414 416 422 423 www.cambridge.org Cambridge University Press 978-1-108-43106-4 — Electrical Machines S. 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Sahdev Frontmatter More Information Contents 5.20 Speed Control of DC Motors 5.21 Speed Control of Shunt Motors 5.21.1 Field Control Method 5.21.2 Armature Control Method 5.22 Speed Control of Separately Excited Motors 5.23 Speed Regulation 5.24 Speed Control of DC Series Motors 5.24.1 Armature Control Method 5.24.2 Field Control Method 5.24.3 Voltage Control Method 5.25 Electric Braking 5.26 Types of Electric Braking 5.26.1 Plugging 5.26.2 Rheostatic Braking 5.26.3 Regenerative Braking Section Practice Problems 5.27 Losses in a DC Machine 5.28 Constant and Variable Losses 5.29 Stray Losses 5.30 Power Flow Diagram 5.31 Efficiency of a DC Machine 5.32 Condition for Maximum Efficiency 5.33 Test Performed to Determine Efficiency of DC Machines 5.34 Brake Test 5.35 Swinburne’s Test 5.36 Hopkinson’s Test 5.37 Testing of DC Series Machines 5.38 Inspection/maintenance of DC Machines 5.39 Faults in DC Machines 5.40 Trouble Shooting in a DC Motor Section Practice Problems Review Questions Multiple Choice Questions 6. Synchronous Generators or Alternators Introduction 6.1 General Aspects of Synchronous Machines 6.2 Basic Principles 6.3 Generator and Motor Action 6.4 Production of Sinusoidal Alternating emf 6.5 Relation between Frequency, Speed and Number of Poles 6.6 Advantages of Rotating Field System over Stationary Field System 6.7 Constructional Features of Synchronous Machines © in this web service Cambridge University Press xiii 428 428 428 429 431 432 440 440 441 442 451 453 453 454 455 457 460 461 461 462 462 463 471 472 474 479 487 491 492 492 493 495 497 500 501 501 502 503 503 504 504 505 www.cambridge.org Cambridge University Press 978-1-108-43106-4 — Electrical Machines S. K. Sahdev Frontmatter More Information xiv Contents 6.8 Excitation Systems 6.8.1 DC Exciters 6.8.2 Static-Excitation System 6.8.3 Brushless Excitation System Section Practice Problems 6.9 Armature Winding 6.10 Types of Armature Winding 6.11 Important Terms Used in Armature Winding Section Practice Problems 6.12 Coil Span Factor 6.13 Distribution Factor 6.14 Winding Factor 6.15 Generation of Three-phase emf 6.16 emf Equation 6.17 Wave Shape 6.18 Harmonics in Voltage Wave Form Section Practice Problems 6.19 Production of Revolving Field 6.20 Ferrari’s Principle (Vector Representation of Alternating Field) 6.21 Production of Two-phase Rotating Magnetic Field 6.22 Production of Three-phase Rotating Magnetic Field 6.23 Rating of Alternators 6.24 Armature Resistance 6.25 Armature Leakage Reactance 6.26 Armature Reaction 6.27 Effect of Armature Reaction on emf of Alternator 6.28 Synchronous Reactance and Synchronous Impedance 6.29 Equivalent Circuit of an Alternator and Phasor Diagram 6.30 Expression for No-load Terminal Voltage 6.31 Voltage Regulation 6.32 Determination of Voltage Regulation 6.33 Synchronous Impedance Method or emf Method 6.33.1 Determination of Synchronous Impedance 6.33.2 Determination of Synchronous Reactance 6.34 Modern Alternators 6.35 Short-Circuit Ratio (SCR) Section Practice Problems 6.36 Assumptions Made in Synchronous Impedance Method 6.37 Ampere-turn (or mmf) Method 6.38 Zero Power Factor or Potier Method Section Practice Problems 6.39 Power Developed by Cylindrical Synchronous Generators © in this web service Cambridge University Press 509 509 510 511 512 513 513 515 519 521 522 524 524 525 526 526 534 535 539 540 541 542 542 543 544 546 548 548 549 551 552 552 553 555 556 556 565 566 567 579 591 592 www.cambridge.org Cambridge University Press 978-1-108-43106-4 — Electrical Machines S. 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Sahdev Frontmatter More Information Contents 6.39.1 Power Output of an AC Generator (in Complex Form) 6.39.2 Real Power Output of an AC Generator 6.39.3 Reactive Power Output of an AC Generator 6.39.4 Power Input to an AC Generator (in Complex Form) 6.39.5 Real Power Input to an AC Generator 6.39.6 Reactive Power Input to an AC Generator 6.39.7 Condition for Maximum Power Output 6.39.8 Condition for Maximum Power Input 6.39.9 Power Equations, when Armature Resistance is Neglected 6.40 Two-Reactance Concept for Salient Pole Synchronous Machines 6.40.1 Determination of Xd and Xq by Low Voltage Slip Test 6.41 Construction of Phasor Diagram for Two-Reaction Concept 6.42 Power Developed by a Salient Pole Synchronous Generator Section Practice Problems 6.43 Transients in Alternators 6.43.1 Sub-transient, Transient and Direct Reactance 6.44 Losses in a Synchronous Machine and Efficiency 6.45 Power Flow Diagram 6.46 Necessity of Cooling 6.47 Methods of Cooling 6.48 Preventive Maintenance Section Practice Problems Review Questions Multiple Choice Questions 7. Parallel Operation of Alternators Introduction 7.1 Necessity of Parallel Operation of Alternators 7.2 Requirements for Parallel Operation of Alternators 7.3 Synchronising Alternators 7.4 Conditions for Proper Synchronising 7.5 Synchronising Single-phase Alternators 7.5.1 Dark Lamp Method 7.5.2 Bright Lamp Method 7.6 Synchronising Three-phase Alternators 7.6.1 Three Dark Lamps Method 7.6.2 Two Bright and One Dark Lamp Method 7.7 Synchronising Three-phase Alternators using Synchroscope 7.8 Shifting of Load 7.9 Load Sharing between Two Alternators Section Practice Problems 7.10 Two Alternators Operating in Parallel 7.11 Synchronising Current, Power and Torque © in this web service Cambridge University Press xv 593 593 594 594 594 595 595 596 596 597 599 600 603 610 611 613 616 617 617 618 619 619 620 622 626 626 626 627 627 627 629 629 631 631 632 633 635 636 637 646 647 647 www.cambridge.org Cambridge University Press 978-1-108-43106-4 — Electrical Machines S. K. Sahdev Frontmatter More Information xvi Contents 7.12 Effect of Change in Input Power of One of the Alternators 7.13 Effect of Change in Excitation of One of the Alternators 7.14 Effect of Reactance 7.15 Effect of Governors’ Characteristics on Load Sharing 7.16 Hunting Section Practice Problems Review Questions Multiple Choice Questions 649 650 651 652 653 660 661 663 8. Synchronous Motors Introduction 8.1 Working Principle of a Three-Phase Synchronous Motor 8.2 Effect of Load on Synchronous Motor 8.3 Equivalent Circuit of a Synchronous Motor 8.4 Phasor Diagram of a Synchronous Motor (Cylindrical Rotor) 8.5 Relation between Supply Voltage V and Excitation Voltage E 8.6 Different Torques in a Synchronous Motor 8.7 Power Developed in a Synchronous Motor (Cylindrical Rotor) 8.8 Phasor Diagrams of a Salient-pole Synchronous Motor 8.9 Power Developed in a Salient-pole Synchronous Motor 8.10 Power Flow in a Synchronous Motor Section Practice Problems 8.11 Effect of Change in Excitation 8.12 V-Curves and Inverted V-Curves 8.13 Effect of Change in Load on a Synchronous Motor 8.14 Methods of Starting of Synchronous Motors 8.15 Synchronous Condenser 8.16 Characteristics of Synchronous Motor 8.17 Hunting 8.18 Applications of Synchronous Motors 8.19 Comparison between Three-phase Synchronous and Induction Motors 8.20 Merits and Demerits of Synchronous Motor Section Practice Problems Review Questions Multiple Choice Questions 665 665 666 667 669 669 671 673 673 676 679 679 700 701 703 704 706 707 710 711 712 712 713 713 716 717 9. Three-Phase Induction Motors Introduction 9.1 Constructional Features of a Three-Phase Induction Motor 9.2 Production of Revolving Field 9.3 Principle of Operation 9.4 Reversal of Direction of Rotation of Three-Phase Induction Motors 9.5 Slip 721 721 722 724 725 726 727 © in this web service Cambridge University Press www.cambridge.org Cambridge University Press 978-1-108-43106-4 — Electrical Machines S. K. Sahdev Frontmatter More Information Contents 9.6 Frequency of Rotor Currents 9.7 Speed of Rotor Field or mmf 9.8 Rotor emf 9.9 Rotor Resistance 9.10 Rotor Reactance 9.11 Rotor Impedance 9.12 Rotor Current and Power Factor 9.13 Simplified Equivalent Circuit of Rotor Section Practice Problems 9.14 Stator Parameters 9.15 Induction Motor on No-load 9.16 Induction Motor on Load 9.17 Induction Motor vs Transformer 9.18 Reasons of Low Power Factor of Induction Motors 9.19 Main Losses in an Induction Motor 9.20 Power Flow Diagram 9.21 Relation between Rotor Copper Loss, Slip and Rotor Input 9.22 Rotor Efficiency Section Practice Problems 9.23 Torque Developed by an Induction Motor 9.24 Condition for Maximum Torque and Equation for Maximum Torque 9.25 Starting Torque 9.26 Ratio of Starting to Maximum Torque 9.27 Ratio of Full Load Torque to Maximum Torque 9.28 Effect of Change in Supply Voltage on Torque 9.29 Torque-slip Curve 9.30 Torque-speed Curve and Operating Region 9.31 Effect of Rotor Resistance on Torque-slip Curve Section Practice Problems 9.32 Constant and Variable Losses in an Induction Motor 9.33 Main Tests Performed on an Induction Motor 9.33.1 Stator Resistance Test 9.33.2 Voltage-ratio Test 9.33.3 No-load Test 9.33.4 Blocked Rotor Test 9.33.5 Heat Run Test 9.34 Equivalent Circuit of an Induction Motor 9.35 Simplified Equivalent Circuit of an Induction Motor 9.36 Maximum Power Output 9.37 Circle Diagram 9.38 Circle Diagram for the Approximate Equivalent Circuit of an Induction Motor 9.39 Construction of a Circle Diagram for an Induction Motor © in this web service Cambridge University Press xvii 728 729 730 730 730 731 731 732 739 740 740 741 742 743 744 744 745 745 752 752 753 754 754 755 755 756 757 757 764 765 766 766 766 767 769 770 773 775 776 781 782 783 www.cambridge.org Cambridge University Press 978-1-108-43106-4 — Electrical Machines S. 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Sahdev Frontmatter More Information xviii Contents 9.40 Results Obtainable from Circle Diagram 9.41 Maximum Quantities 9.42 Significance of Some Lines in the Circle Diagram Section Practice Problems 9.43 Effect of Space Harmonies 9.43.1 Cogging in Three-phase Induction Motors 9.43.2 Crawling in Three-phase Induction Motors 9.44 Performance Curves of Induction Motors 9.45 Factors Governing Performance of Induction Motors 9.46 High Starting Torque Cage Motors 9.46.1 Deep Bar Cage Rotor Motors 9.46.2 Double Cage Induction Motor 9.47 Motor Enclosures 9.48 Standard Types of Squirrel Cage Motor 9.48.1 Class A Motors 9.48.2 Class B Motors 9.48.3 Class C Motors 9.48.4 Class D Motors 9.48.5 Class E Motors 9.48.6 Class F Motors 9.49 Advantages and Disadvantages of Induction Motors 9.49.1 Squirrel Cage Induction Motors 9.49.2 Slip-ring Induction Motors 9.50 Applications of Three-phase Induction Motors 9.51 Comparison of Squirrel Cage and Phase Wound Induction Motors 9.52 Comparison between Induction Motor and Synchronous Motor 9.53 Installation of Induction Motors 9.54 Preventive Maintenance of Three-phase Induction Motors Section Practice Problems Review Questions Multiple Choice Questions 10. Starting Methods and Speed Control of Three-phase Induction Motors Introduction 10.1 Necessity of a Starter 10.2 Starting Methods of Squirrel Cage Induction Motors 10.2.1 Direct on Line (D.O.L.) Starter 10.2.2 Stator Resistance (or Reactance) Starter 10.2.3 Star-Delta Starter 10.2.4 Auto-transformer Starter 10.3 Rotor Resistance Starter for Slip Ring Induction Motors Section Practice Problems 10.4 Speed Control of Induction Motors © in this web service Cambridge University Press 785 785 786 793 795 795 795 796 798 798 799 800 807 810 811 811 811 812 812 813 813 813 814 814 815 815 816 818 819 820 822 828 828 829 829 829 831 832 834 836 844 844 www.cambridge.org Cambridge University Press 978-1-108-43106-4 — Electrical Machines S. K. Sahdev Frontmatter More Information Contents 10.5 Speed Control by Changing the Slip 10.5.1 Speed Control by Changing the Rotor Circuit Resistance 10.5.2 Speed Control by Controlling the Supply Voltage 10.5.3 Speed Control by Injecting Voltage in the Rotor Circuit 10.6 Speed Control by Changing the Supply Frequency 10.7 Speed Control by Changing the Poles 10.8 Speed Control by Cascade Method 10.9 Speed Control by Injecting an emf in the Rotor Circuit 10.9.1 Kramer System of Speed Control 10.9.2 Scherbius System of Speed Control Section Practice Problems Review Questions Multiple Choice Questions xix 845 845 846 847 847 847 848 850 851 851 854 854 855 11. Single-Phase Motors Introduction 11.1 Classification of Single-phase Motors 11.2 Single-phase Induction Motors 11.3 Nature of Field Produced in Single Phase Induction Motors 11.4 Torque Produced by Single-phase Induction Motor 11.5 Equivalent Circuit of Single-phase Induction Motor 11.6 Rotating Magnetic Field from Two-phase Supply 11.7 Methods to make Single-phase Induction Motor Self-starting 11.8 Split Phase Motors 11.9 Capacitor Motors Section Practice Problems 11.10 Shaded Pole Motor 11.11 Reluctance Start Motor 11.12 Single-phase Synchronous Motors 11.13 Reluctance Motors 11.14 Hysteresis Motors 11.15 AC Series Motor or Commutator Motor 11.16 Universal Motor 11.17 Comparison of Single-phase Motors 11.18 Trouble Shooting in Motors Section Practice Problems Review Questions Multiple Choice Questions 857 857 857 858 859 860 861 866 870 871 875 878 879 880 881 882 884 885 886 888 889 890 891 892 12. Special Purpose Machines Introduction 12.1 Feedback Control System 12.2 Servomechanism 893 893 893 894 © in this web service Cambridge University Press www.cambridge.org Cambridge University Press 978-1-108-43106-4 — Electrical Machines S. K. Sahdev Frontmatter More Information xx Contents 12.3 Servomotors 12.4 DC Servomotors 12.4.1 Field-controlled DC Servomotors 12.4.2 Armature-controlled DC Servomotors 12.4.3 Series Split-field DC Servomotors 12.4.4 Permanent-magnet Armature-controlled DC Servomotor 12.5 AC Servomotors 12.6 Schrage motor Section Practice Problems 12.7 Brushless Synchronous Generator 12.7.1 Brushless DC Generator 12.8 Brushless Synchronous Motor 12.9 Three-brush (or Third-brush) Generator 12.10 Brushless DC Motors 12.11 Stepper Motors 12.11.1 Permanent-magnet (PM) Stepper Motor 12.11.2 Variable-reluctance (VR) Stepper Motor Section Practice Problems 12.12 Switched Reluctance Motor (SRM) 12.13 Linear Induction Motor (LIM) 12.14 Permanent Magnet DC Motors 12.15 Induction Generator 12.16 Submersible Pumps and Motors 12.17 Energy Efficient Motors Section Practice Problems Review Questions Multiple Choice Questions Open Book Questions Index © in this web service Cambridge University Press 894 895 895 895 896 896 897 898 903 903 905 905 906 907 908 909 912 913 914 915 917 920 922 926 929 929 930 933 949 www.cambridge.org Cambridge University Press 978-1-108-43106-4 — Electrical Machines S. K. Sahdev Frontmatter More Information Preface This book on ‘Electrical Machines’ has been written for under-graduate students of Electrical Engineering (EE) and Electrical & Electronics Engineering (EEE) belonging to various Indian and Foreign Universities. It will also be useful to candidates appearing for AMIE, IETE, GATE, UPSC Engineering Services and Civil Services Entrance Examinations. We know that electrical energy has a wide range of applications where electrical machines play a vital role in industrial production and many other areas of science and technology. Accordingly, this book has been designed so that it be useful not only to students pursuing courses in electrical engineering but also for practising engineers and technicians. ‘Electrical Machines’ is taught at various universities under different titles such as Electrical Machines-I, Electrical Machines-II, DC Machines and Transformers, Electromagnetic Energy Conversion Devices, Special Purpose Machines, etc. All the topics in such courses have been covered in this single unit. As such, the book covers the revised syllabi of all Indian and Foreign Universities. Generally, students find Electrical Machines to be one of the most difficult subjects to understand, despite the availability of a large number of text books in this field. Keeping this fact in mind, this text has been developed in a systematic manner giving more emphasis on basic concepts. Each chapter of the book contains much needed text, supported by neat and self-explanatory diagrams to make the subject self-speaking to a great extent. A large number of solved and unsolved examples have been added in various chapters to enable students to attempt different types of questions in examination without any difficulty. Section Practice Problems have been added in all the chapters to maintain regular study and understanding. At the end of each chapter sufficient objective type questions, short-answer questions, test questions and unsolved examples have been added to make the book a complete and comprehensive unit in all respects. The author lays no claim to original research in preparing the text. Materials available in the research work of eminent authors have been used liberally. But the author claims that he has organised the subject matter in very systematic manner. He also claims that the language of the text is lucid, direct and easy to understand. Although every care has been taken to eliminate errors, however it is very difficult to claim perfection. I hope this book will be useful to its users (students, teachers and professionals). I shall be very grateful to the readers (students and teachers) and users of this book if they point out any mistake that might have crept in. Suggestions for the improvement of the book will be highly appreciated. © in this web service Cambridge University Press www.cambridge.org Cambridge University Press 978-1-108-43106-4 — Electrical Machines S. K. Sahdev Frontmatter More Information Acknowledgements There are several people to whom I would like to express my sincere thanks. First of all, I would like to thank Mr Ashok Mittal (Hon’ble Chancellor), Mrs Rashmi Mittal (Hon’ble Pro-chancellor), Mr H. R. Singla (Director General) of Lovely Professional University, Jalandhar, who have inspired me to develop the text in the shape of a book. I would also like to thank Dr Lovi Raj Gupta, Executive Dean, (LFTS) of Lovely Professional University, who has encouraged and helped me in preparing the text. Secondly, I would like to thank the entire executive staff, faculty and students of Lovely Professional University and Punjab Technical University for their support, collaboration and friendship. I would like to thank all my friends, particularly Dr Manjo Kumar, Principal, DAV Institute of Engineering and Technology, Jalandhar; Dr Sudhir Sharma, HOD, Electrical, DAV Institute of Engineering and Technology, Jalandhar; Mr D. S. Rana, HOD, Electrical who have been involved, either directly or indirectly, in the successful completion of this book. I owe my family members, relatives, friends and colleagues (Professor Bhupinder Verma, Mr R. K. Sharma, Mr Satnam Singh, Mr Amit Dhir and Ms Meenakshi Gupta) a special word of thanks for their moral support and encouragement. I express my gratitude to the Publisher ‘Cambridge University Press’ and its Associate Commissioning Editor Ms Rachna Sehgal for guidance and support in bringing out the text in the shape of a book. © in this web service Cambridge University Press www.cambridge.org
