Introduction to ELECTRICAL

POWER and POWER

ELECTRONICS

MUKUND R PATEL

( c J * CRC Press Taylor & Francis Group

Boca Raton London New York

CRC Press is an imprint of the Taylor & Francis Croup, an informa business

Contents Preface xv Acknowledgments xvii The Author xix About This Book xxi Systems of Units and Conversion Factors xxiii

PART A Power Generation, Distribution, and Utilization

Chapter 1 AC Power Fundamentals 3

1.1 Current Voltage Power and Energy 3 1.2 Alternating Current 4

1.2.1 RMS Value and Average Power 5 1.2.2 Polarity Marking in AC 6

1.3 ACPhasor 7 1.3.1 Operator; for 90° Phase Shift 9 1.3.2 Three Ways of Writing aPhasor 10 1.3.3 Phasor Form Conversion 11

1.4 Phasor Algebra Review 11 1.5 Single-Phase AC Power Circuit 14

1.5.1 Series R-L-C Circuit 15 1.5.2 Impedance Triangle 19 1.5.3 Circuit Laws and Theorems 21

1.6 AC Power in Complex Form 23 1.7 Reactive Power 27 1.8 Three-Phase AC Power System 28

1.8.1 Balanced Y- and A-Connected Systems 28 1.8.2 Y-A Equivalent Impedance Conversion 31

Further Reading 37

Chapter 2 Common Aspects of Power Equipment 39

2.1 Faraday's Law and Coil Voltage Equation 39 2.2 Mechanical Force and Torque 41 2.3 Electrical Equivalent of Newton's Third Law 43 2.4 Power Losses in Electrical Machines 43 2.5 Maximum Efficiency Operating Point 44 2.6 Thevenin Equivalent Source Model 46

vii

viii Contents

2.7 Voltage Drop and Regulation 48 2.8 Load Sharing among Sources 51

2.8.1 Static Sources in Parallel 51 2.8.2 Load Adjustment 54

2.9 Power Rating of Equipment 54 2.9.1 Temperature Rise under Load 55 2.9.2 Service Life under Overload 55

2.10 Temperature Effect on Resistance 56 Further Reading 60

Chapter 3 AC Generator 61

3.1 Terminal Performance 62 3.2 Electrical Model 63 3.3 Electrical Power Output 64

3.3.1 Field Excitation Effect 68 3.3.2 Power Capability Limits 69 3.3.3 Round and Salient Pole Rotors 70

3.4 Transient Stability Limit 72 3.5 Equal Area Criteria of Transient Stability 74 3.6 Speed and Frequency Regulations 78 3.7 Load Sharing among AC Generators 80 3.8 Isosynchronous Generator 82 3.9 Excitation Methods 84 3.10 Short Circuit Ratio 86 3.11 Automatic Voltage Regulator 86 Further Reading 90

Chapter 4 AC and DC Motors 91

4.1 Induction Motor 92 4.1.1 Performance Characteristics 96 4.1.2 Starting Inrush Kilovolt-Ampere Code 100 4.1.3 Torque-Speed Characteristic Matching 102 4.1.4 Motor Control Center 104 4.1.5 Performance at Different Frequency and Voltage.... 104

4.2 Synchronous Motor 106 4.3 Motor Horsepower and Line Current 110 4.4 Dual-Use Motors Ill 4.5 Unbalanced Voltage Effect 113 4.6 DC Motor 116 4.7 Universal (Series) Motor AC or DC 118 4.8 Torque versus Speed Comparison 119 Further Reading 122

Contents ix

Chapter 5 Transformer 123

5.1 Transformer Categories 124 5.2 Types of Transformer 125 5.3 Selection of Kilovolt-Ampere Rating 128 5.4 Transformer Cooling Classes 129 5.5 Three-Phase Transformer Connections 130 5.6 Full-A and Open-A Connections 131 5.7 Magnetizing Inrush Current 132 5.8 Single-Line Diagram Model 134 5.9 Three-Winding Transformer 136 5.10 Percent and Perunit Systems 137 5.11 Equivalent Impedance at Different Voltage 141 5.12 Continuous Equivalent Circuit through Transformer 143 5.13 Influence of Transformer Impedance 145 Further Reading 149

Chapter 6 Power Cable 151

6.1 Conductor Gage 151 6.2 Cable Insulation 153 6.3 Conductor Ampacity 155 6.4 Cable Electrical Model 158 6.5 Skin and Proximity Effects 160 6.6 Cable Design 162 6.7 Cable Routing and Installation 171 Further Reading 173

Chapter 7 Power Distribution 175

7.1 Typical Distribution Scheme 175 7.2 Grounded and Ungrounded Systems 176 7.3 Ground Fault Detection Schemes 179 7.4 Distribution Feeder Voltage Drop 180

7.4.1 Voltage Drop during Motor Starting 181 7.4.2 Voltage Boost by Capacitors 182 7.4.3 System Voltage Drop Analysis 184

7.5 Bus Bar Electrical Parameters 185 7.6 High Frequency Distribution 186 7.7 Switchboard and Switchgear 190

7.7.1 Automatic Bus Transfer 191 7.7.2 Disconnect Switch 192

Further Reading 194

x Contents

Chapter 8 Fault Current Analysis 195

8.1 Types and Frequency of Faults 195 8.2 Fault Analysis Model 196 8.3 Asymmetrical Fault Transient 198

8.3.1 Simple Physical Explanation 199 8.3.2 Rigorous Mathematical Analysis 200

8.4 Fault Current Offset Factor 200 8.5 Fault Current Magnitude 202

8.5.1 Symmetrical Fault Current 202 8.5.2 Asymmetrical Fault Current 203 8.5.3 Transient and Subtransient Reactance 207 8.5.4 Generator Terminal Fault Current 212 8.5.5 Transformer Terminal Fault Current 212

8.6 Motor Contribution to Fault Current 213 8.7 Current-Limiting Series Reactor 215 8.8 Unsymmetrical Faults 215 8.9 Circuit Breaker Selection Simplified 216 Further Reading 220

Chapter 9 System Protection 221

9.1 Fuse 222 9.1.1 Fuse Selection 223 9.1.2 Types of Fuse 224

9.2 Overload Protection 227 9.3 Electromechanical Relay 228 9.4 Circuit Breaker 230

9.4.1 Types of Circuit Breaker 232 9.4.2 Circuit Breaker Selection 236 9.4.3 Standard Ratings of LV Breaker 238

9.5 Differential Protection of Generator 238 9.6 Differential Protection of Bus and Feeders 239 9.7 Ground Fault Current Interrupter 240 9.8 Transformer Protection 241 9.9 Motor Branch Circuit Protection 241 9.10 Lightning and Switching Voltage Protection 243 9.11 Surge Protection for Small Sensitive Loads 247 9.12 Protection Coordination 249 9.13 Health Monitoring 249 9.14 Arc Flash Analysis 250 Further Reading 253

Contents xi

Chapter 10 Economical Use of Power 255

10.1 Economic Analysis 255 10.1.1 Cashflow with Borrowed Capital 255 10.1.2 Payback of Self-Financed Capital 256

10.2 Power Loss Capitalization 259 10.3 High-Efficiency Motor 260 10.4 Power Factor Improvement 263

10.4.1 Capacitor Size Determination 267 10.4.2 Parallel Resonance with Source 270 10.4.3 Safety with Capacitors 271 10.4.4 Difference between PF and Efficiency 272

10.5 Energy Storage 273 10.6 Variable-Speed Motor Drives 273 10.7 Regenerative Braking 274

10.7.1 Induction Motor Torque versus Speed Curve 275 10.7.2 Induction Motor Braking 276 10.7.3 DC Motor Braking 279 10.7.4 New York and Oslo Metro Trains 281

Further Reading 285

Chapter 11 Electrochemical Battery 287

11.1 Major Rechargeable Batteries 289 11.1.1 Lead-Acid 289 11.1.2 Nickel-Cadmium 290 11.1.3 Nickel-Metal Hydride 291 11.1.4 Lithium Ion 291 11.1.5 Lithium Polymer 292 11.1.6 Sodium Battery 292

11.2 Electrical Circuit Model 292 11.3 Performance Characteristics 293

11.3.1 Charge/Discharge Voltages 294 11.3.2 c/d Ratio and Charge Efficiency 294 11.3.3 Round-Trip Energy Efficiency 294 11.3.4 Self-Discharge and Trickle Charge 296 11.3.5 Memory Effect in NiCd 297 11.3.6 Temperature Effects 297

11.4 Battery Life 297 11.5 Battery Types Compared 300 11.6 More on Lead-Acid Battery 300 11.7 Battery Design Process 301 11.8 Safety and Environment 303 Further Reading 306

xii Contents

PART B Power Electronics and Motor Drives

Chapter 12 Power Electronics Devices 309

12.1 Diode 314 12.2 Thyristor (SCR) 318 12.3 Power Transistor 320 12.4 Hybrid Devices 323 12.5 di/dt and dv/dt Snubber Circuit 324 12.6 Switching Power Loss 327 12.7 Device Application Trends 330 12.8 Device Cooling and Rerating 331 Further Reading 333

Chapter 13 DC-DC Converters 335

13.1 Buck Converter 335 13.2 Boost Converter 342 13.3 Buck-Boost Converter 343 13.4 Flyback Converter (Buck or Boost) 345 13.5 Transformer Coupled Forward Converter 346 13.6 Push-Pull Converter 347 13.7 Inductor Coupled Buck Converter 347 13.8 Duty Ratio Control Circuit 348 13.9 Load Power Converter 349 13.10 Power Supply 350 Further Reading 353

Chapter 14 AC-DC-AC Converters 355

14.1 AC-DC Rectifier 355 14.1.1 Single-Phase Full-Wave Rectifier 355 14.1.2 Ripples in DC and Ripple Factor 360 14.1.3 Harmonics in AC and Root Sum Square 360 14.1.4 Harmonic Distortion Factor 361 14.1.5 Three-Phase Six-Pulse Rectifier 364

14.2 AC-AC Voltage Converter 368 14.2.1 Single-Phase Voltage Converter 368 14.2.2 Three-Phase Voltage Converter 369

14.3 DC-AC Inverter 370 14.3.1 Single-Phase Voltage Source Inverter 370 14.3.2 Single-Phase Pulse with Modulated Inverter 374 14.3.3 Three-Phase Six-Pulse Voltage Source Inverter 377 14.3.4 Three-Phase Six-Pulse Current Source Inverter 378

14.4 Frequency Converter 380 14.4.1 DC-Link Frequency Converter 381

Contents xiii

14.4.2 Single-Phase Cycloconverter 382 14.4.3 Three-Phase Cycloconverter 384

14.5 Thyristor Turnoff (Commutation) Circuits 385 14.5.1 Line Commutation 385 14.5.2 Forced (Capacitor) Commutation 385 14.5.3 Resonant Commutation 386 14.5.4 Load Commutation 386 14.5.5 ZCSandZVS 387

14.6 Other Power Electronics Applications 387 14.6.1 Uninterruptible Power Supply 387 14.6.2 Static WAR Control 387 14.6.3 Static Switch and Relay 389

14.7 Common Converter Terms 389 14.8 Notes on Converter Design 390 Further Reading 395

Chapter 15 Variable-Frequency Drives 397

15.1 Pump Performance Characteristics 398 15.2 Pump Energy Savings with VFD 400 15.3 VFD on Ships and in Oil Refineries 404 15.4 VFD for Medium-Size Motor 404 15.5 Constant W/Ratio Operation 407 15.6 Commutation and Control Methods 413 15.7 Open-Loop Control System 414 15.8 Vector Control Drives 415 15.9 Twelve-Pulse VFD Design 417 15.10 Special VFD Cables 417 15.11 Variable-Voltage DC Motor Drive 423 15.12 VSD in Metro Trains 424 15.13 VFD as Large Motor Starter 424 15.14 Converter Topologies Compared 426 15.15 Notes on VFDs 427 Further Reading 429

Chapter 16 Quality of Power 431

16.1 Power Quality Terminology 431 16.2 Electrical Bus Model 433 16.3 Harmonics 436

16.3.1 Harmonic Power 438 16.3.2 THD and Power Factor 440 16.3.3 ^-Rated Transformer 443 16.3.4 Motor Torque Pulsations 445 16.3.5 Harmonic-Sensitive Loads 448

16.4 Power Quality Studies 449

xiv Contents

16.5 Harmonic Reduction 451 16.5.1 Harmonic Filter Design 451 16.5.2 Very Clean Power Bus 456 16.5.3 A-Connected Transformer 457 16.5.4 Cable Shielding and Twisting 458 16.5.5 Isolation Transformer 459

16.6 IEEE Standard 519 460 16.7 International Standards 461 Further Reading 464

Chapter 17 Power Converter Cooling 465

17.1 Heat Transfer by Conduction 465 17.2 Multiple Conduction Paths 467 17.3 Convection and Radiation 470 17.4 Thermal Transient 471 17.5 Water Cooling 473

17.5.1 Cooling Tube Design 474 17.5.2 Pressure Drop 475 17.5.3 Cooling Water Quality 480

Further Reading 482

Appendix: Symmetrical Components 483

Index 491