HIGH VOLTAGE CIRCUIT BREAKERS

Design and Applications

Second Edition, Revised and Expanded

RUBEN D. GARZON Square D Co.

Smyrna, Tennessee

M A R C E L

Ш D E К К E R

MARCEL DEKKER, INC. N E W YORK • BASEL

CONTENTS

Preface to the Second Edition v

Preface to the First Edition vii

1 Electric Arc Fundamentals 1 1.0 Introduction 1 1.1 Basic Theory of Electrical Discharges 2

1.1.1 Non-Self-Sustaining Discharges 2 1.1.2 Self-Sustaining Discharges 4

1.2 The Electric Arc 5 1.2.1 High-Pressure Arcs 5 1.2.2 Low-Pressure (Vacuum) Arcs 8

1.3 The Alternating Current Arc 9 1.4 The Current Interruption Process 10

1.4.1 Interruption of Direct Current 11 1.4.2 Interruption of Alternating Currents 13

1.5 Review of Main Theories of AC Interruption 18 1.5.1 Slepian's Theory 19 1.5.2 Prince's Theory 20 1.5.3 Cassie's Theory 21 1.5.4 Mayr's Theory 22 1.5.5 Browne's Combined Theory 23 1.5.6 Modern Theories 24

References 25

2 Short Circuit Currents 27 2.0 Introduction 27 2.1 Characteristics of the Short Circuit Current 27

2.1.1 Transient Direct Current Component 28 2.1.2 The Volt-Time Area Concept 30 2.1.3 Transient Alternating Current Components 32 2.1.4 Asymmetry of Three-Phase Short Circuit Currents 34 2.1.5 Measuring Asymmetrical Currents 36

2.2 Calculation of Short Circuit Currents 40

xi

xii Contents

2.2.1 The Per Unit Method 40 2.2.2 The MVA Method 48

2.3 Unbalanced Faults 50 2.3.1 Introduction to Symmetrical Components 51

2.4 Forces Produced by the Short Circuit Currents 55 2.4.1 Direction of the Forces Between Current Carrying Conductors 56 2.4.2 Calculation of Electrodynamic Forces Between Conductors 63 2.4.3 Forces on Conductors Produced by Three-Phase Currents 69

References 72

3 Transient Recovery Voltage 75 3.0 Introduction 75 3.1 Transient Recovery Voltage: General Concepts 76

3.1.1 Basic Assumptions for TRV Calculations 78 3.1.2 Current Injection Technique 78 3.1.3 Traveling Waves and the Lattice Diagram 79

3.2 Calculation of Transient Recovery Voltages 83 3.2.1 Single Frequency Recovery Voltage 83 3.2.2 Double Frequency Recovery Voltage: General Case 88 3.2.3 Particular Case of Double Frequency Recovery Voltage 97 3.2.4 Short-Line Fault Recovery Voltage 101 3.2.5 Initial Transient Recovery Voltage 104

References 106

4 Switching Overvoltages 107 4.0 Introduction 107 4.1 Contacts Closing 108

4.1.1 Closing of a Line 109 4.1.2 Reclosingof a Line 112 4.1.3 Energizing Unloaded Transformers 113

4.2 Contact Opening 114 4.2.1 Interruption of Small Capacitive Currents 115 4.2.2 Interruption of Inductive Load Currents 117 4.2.3 Current Chopping 119 4.2.4 Virtual Current Chopping 122 4.2.5 Temporary Overvoltages 124 4.2.6 Controlling Overvoltages 125

References 126

5 Types of Circuit Breakers 129 5.0 Introduction 129 5.1 Circuit Breaker Classifications 130

5.1.1 Circuit Breaker Types by Voltage Class 130 5.1.2 Circuit Breaker Types by Installations 130

Contents xiii

5.1.3 Circuit Breaker Types by External Design 132 5.1.4 Circuit Breaker Types by Interrupting Mediums 132

5.2 Air Magnetic Circuit Breakers 134 5.2.1 Arc Chute Type Circuit Breakers 135 5.2.2 Air Magnetic Circuit Breaker Typical Applications 141

5.3 Air Blast Circuit Breakers 141 5.3.1 Blast Direction and Nozzle Types 142 5.3.2 Series Connection of Interrupters 145 5.3.3 Basic Interrupter Arrangements 146 5.3.4 Parameters Influencing Air Blast Circuit Breaker Performance 146

5.4 Oil Circuit Breakers 149 5.4.1 Properties of Insulating Oil 150 5.4.2 Current Interruption in Oil 150 5.4.3 Types of Oil Circuit Breakers 152 5.4.4 Bulk Oil Circuit Breakers 156 5.4.5 Minimum Oil Circuit Breakers 159

5.5 Sulfurhexafluoride 161 5.5.1 Properties of SF6 162 5.5.2 Arc Decomposed By-Products 164 5.5.3 SF6 Environmental Considerations 165 5.5.4 Recycling of SF6 167 5.5.5 Current Interruption in SF6 168 5.5.6 Two Pressure SF6 Circuit Breakers 170 5.5.7 Single Pressure SF6 Circuit Breakers 172 5.5.8 Pressure Increase of SF6 Produced by an Electric Arc 176 5.5.9 Parameters Influencing SF6 Circuit Breaker Performance 179 5.5.10 SF6-Nitrogen Gas Mixture 182

5.6 Vacuum Circuit Breakers 183 5.6.1 Current Interruption in Vacuum Circuit Breakers 184 5.6.2 Vacuum Interrupter Construction 190 5.6.3 Vacuum Interrupter Contact Materials 191 5.6.4 Interrupting Capability of Vacuum Interrupters 193

References 193

6 Mechanical Design 197 6.0 Introduction 197 6.1 Contact Theory 198

6.1.1 Contact Resistance 198 6.1.2 Insulating Film Coatings on Contacts 200 6.1.3 Contact Fretting 202 6.1.4 Temperature at the Point of Contact 202 6.1.5 Short Time Heating of Copper 203 6.1.6 Electromagnetic Forces on Contacts 205 6.1.7 Contact Erosion 210

XIV Contents

6.2 Mechanical Operating Characteristics 212 6.2.1 Circuit Breaker Opening Requirements 212 6.2.2 Closing Speed Requirements 216

6.3 Operating Mechanisms 217 6.3.1 Cam Versus Linkage 218 6.3.2 Weld Break and Contact Bounce 219 6.3.3 Spring Mechanisms 220 6.3.4 Pneumatic Mechanisms 222 6.3.5 Hydraulic Mechanisms 223 6.3.6 Magnetic Mechanism 226

References 227

7 Dielectric Design 229 7.0 Introduction 229 7.1 Fundamentals of Dielectric Theory 230

7.1.1 Electric Fields 230 7.2 Types of Insulation 239

7.2.1 Gaseous Insulation General Principles 239 7.2.2 Paschen'sLaw 240 7.2.3 Factors Influencing Dielectric Strength 241

7.3 Air Insulation 243 7.4 SF6 Insulation 244

7.4.1 Simplified Design Approach 246 7.5 Vacuum Insulation 247 7.6 Solid Insulation 248

7.6.1 Solid Insulation: Basic Concepts 249 7.6.2 Dielectric Loss 250 7.6.3 Layered Insulation 251 7.6.4 Partial Discharges 252 7.6.5 Insulating Materials 253 7.6.6 Solid Insulation Design Guidelines 256

References 257

8 A Comparison of High Voltage Circuit Breaker Standards 259 8.0 Introduction 259 8.1 Recognized Standards Organizations 260

8.1.1 ANSHEEE/NEMA 260 8.1.2 International Electrotechnical Commission (IEC) 264

8.2 Circuit Breaker Standards and Ratings Comparisons 266 8.2.1 Normal Operating Conditions 266 8.2.2 Rated Power Frequency 267

8.3 Voltage Related Ratings 267 8.3.1 Maximum Operating Voltage 267 8.3.2 Rated Voltage Range Factor К 269

Contents xv

8.3.3 Rated Dielectric Strength 8.3.4 Rated Transient Recovery Voltage

8.4 Current Related Ratings and Requirements 8.4.1 Preferred Number Series 8.4.2 Rated Continuous Current 8.4.3 Rated Short Circuit Current

8.5 Additional Switching Duties 8.5.1 Capacitance Switching

8.6 Mechanical Requirements 8.6.1 Mechanical Operating Life

References

9 Short Circuit Testing 9.0 Introduction 9.1 Test Methodology

9.1.1 Direct Tests 9.1.2 Indirect Tests 9.1.3 Single Phase Tests 9.1.4 Unit Tests 9.1.5 Two Part Tests 9.1.6 Synthetic Tests

9.2 Test Measurements and Procedures 9.2.1 Measured Parameters and Test Set-Up 9.2.2 Test Sequences

References

10 Circuit Breaker Applications 10.0 Introduction 10.1 Overload Currents and Temperature Rise

10.1.1 Effects of Solar Radiation 10.1.2 Continuous Overload Capability 10.1.3 Short Time Overloads 10.1.4 Maximum Continuous Current at High Altitude Applications

10.2 Interruption of Current from High X/R Circuits 10.3 Generator Circuit Breaker Applications

10.3.1 Short Circuit Current Ratings 10.3.2 Generator Asymmetrical Short Circuit Current Calculation 10.3.3 Transient Recovery Voltage

10.4 Application Frequencies Other Than 50 or 60 Hertz 10.5 Capacitance Switching Applications

10.5.1 Open Line 10.5.2 Isolated Cable 10.5.3 Back-to-Back Cables 10.5.4 Isolated Shunt Capacitor Bank

269 276 282 282 282 285 290 290 292 292 293

295 295 297 301 302 302 304 305 306 311 312 314 327

329 329 330 331 332 333 335 335 345 345 351 352 353 354 356 358 358 360

xvi Contents

10.5.5 Back-to-Back Capacitor Banks 363 10.5.6 General Application Guidelines 363 10.5.7 Circuit Breaker Characteristics 357

10.6 Reactor Current Switching, High TRV Applications 368 10.7 Ferroresonance 369 10.8 High Altitude Dielectric Considerations 370 10.9 Reclosing Duty Derating Factors 372 10.10 Vacuum Circuit Breaker Applications 373

10.10.1 Transformer Circuits 375 10.10.2 Applications in Motor Circuits 376 10.10.3 Review of Surge Protection Methods 378

10.11 Choosing Between Vacuum or SF6 379 References 379

11 Synchronous Switching and Condition Monitoring 381 11.0 Introduction 381 11.1 Synchronous Switching 382

11.1.1 Mechanical Performance Considerations 382 11.1.2 Contact Gap Voltage Withstand 385 11.1.3 Synchronous Capacitance Switching 386 11.1.4 Synchronous Reactor Switching 391 11.1.5 Synchronous Transformer Switching 393 11.1.6 Synchronous Short Circuit Current Switching 394

11.2 Condition Monitoring of Circuit Breakers 398 11.2.1 Choice of Monitored Parameters 400 11.2.2 Mechanical Parameters 401 11.2.3 Electrical Parameters 407

11.3 Monitored Parameters Selection Analysis 410 11.4 Monitored Signals Management 413 11.5 Cost-Benefit Analysis 414 References 417

Appendix: Conversion Tables 419

Index 425