Electric Power Distribution
A S Pabla
Consulting Engineerand
Former Chief Engineer Punjab State Electricity Board
McGraw-Hill
New York Chicago San Francisco Lisbon London Madrid Mexico City Milan New Delhi San Juan
Contents
Preface
1. Power System
1.1 General Concept 7 1.2 Distribution of Power 4 1.3 Quality of Supply 12 1.4 System Study 15 1.5 Benchmarking 16 1.6 Electricity Reforms 19
1.7 Future Distribution Systems 20
Problems 24 Bibliography 24
2. Electricity Forecasting
2.1 Power Loads 26 2.2 Connected Load 33 2.3 Load Forecasting 41
2.4 Definitions of Some Basic Concepts in Statistics 2.5 Regression Analysis 45
2.6 Correlation Theory 50 2.7 Analysis of Time Series 51
2.8 Factors in Power System Loading 56 2.9 Unloading the System 59
2.10 Forecast of System Peak 63 2.11 Strategic Forecasting (10) 66
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26
Contents
2.12 Spatial Load Forecasting 67 2.13 Technological Forecasting 69
2.14 Sources of Error: Regulating the Model 72 Problems 72
Bibliography 73
3. System Planning 74
3.1 Planning Process 743.2 Planning Criteria and Standards 81 3.3 System Development 83
3.4 Dispersed Generation 89
3.5 Distribution System Economics and Finance 92 3.6 Mapping 96
; 3.7 Enterprise Resource Planning (ERP) 100
3.8 Modelling 103
3.9 System Calculations 104 3.10 Introductory Methods 107 3.11 Network Elements 7 72 3.12 Load Flow 777
3.13 Automated Planning 123 3.14 Fault Studies 131
3.15 Effect of Abnormal Loads 139 3.16 line Circuits 140
3.17 Urban Distribution 742 3.18 Outsourcing 143
Problems 144 Bibliography 145
4. Design and Operation 147
4.1 Engineering Design 1474.2 Operation Criteria and Standards 757 4.3 Sub-transmission 153
4.4 Sub-station and Feeder 156
4.5 Low Voltage-Three-phase or Single-phase 162 4.6 Practices 164
4.7 Location of Sectionalizer 767 4.8 Voltage Control 168
4.9 Harmonics 178 4.10 Load Variations 189
Contents
ix
'4.11 Impact Loading of Transformer 4.12 Ferroresonance 197
4.13 System Losses 199 4.14 Energy Management 276" 4.15 Model Distribution System 218
Problems 220 Bibliography 221
197
5. Distribution Automation
223223
5.1 Distribution Automation (DA) 5.2 Project Planning 225 5.3 Definitions 227 5.4 Communication 232
/ ,5.5 Sensors 246
5.6 Supervisory Control and Data Acquisition (SCADA) 5.7 Consumer Information Service (CIS) 253
5.8 Geographical Information System (GIS) 254
5.9 Automatic Meter Reading (AMR) 254
5.10 Automation Systems 255 Problems 261
Bibliography 262
6. Optimization
6.1 Introduction 264 6.2 Costing of Schemes 265
Typical Network Configurations 277 Planning Terms 273
Network Cost Modelling 274 Voltage Levels 282
Synthesis of Optimum Line Networks 285 Applications of Linear Programming to Network Synthesis 292
Optimum Phasing Sequence 294
Economic Loading of Distribution Transformers 295 Worst-Case Loading of Distribution Transformers 303 Discussion 305 Problems 306 Bibliography 306 249 264 6.3 6.4 6.5 6.6 6.7 6.8 6.9 6.10 6.12
X Contents
7. Reliability and Quality 308
7.1 Introduction 3087.2 Definition of Reliability 310 7.3 Failure 310
7.4 Probability Concepts 312
7.5 Limitations of Distribution Systems 317 7.6 Power Quality 320
7.7 Reliability Measurement 326
7.8 Power Supply Quality Survey [3] 333 7.9 Reliability Aids 334
Problems 341 Bibliography 341
8. Consumer Services 343
8.1 Supply Industry 343 8.2 Natural Monopoly 343 8.3 Regulations 344
8.4 Other Legal Provisions 349 8.5 Distribution Code 351 8.6 Consumer Care 352 8.7 Standards 353
8.8 Consumer Load Requirements 354 8.9 Consumer Factors 354
8.10 Least Cost of Supply 358 8.11 Revenue and Return 358 8.12 Load Management [2] 359 8.13 Energy Audit 375
8.14 Theft of Electricity 382 8.15 Metering of Energy 386
8.16 Periodical Testing of Meters 357 8.17 Consumer Load Monitoring 399
Problems 399 Bibliography 400
9. Tariffs and Billing 402
9.1 Objectives 402 9.2 Costing 404
Contents XI 9.4 Classifications 412
9.5 Economically Efficient Tariff Structure 418 9.6 Electricity Market 420
9.7 Rational Tariffs 422 9.8 Tariff Applications 424 9.9 Billing 437
Problems 442 Bibliography 443
10. Grounding
10.1 Grounding System 444 10.2 Earth and Safety 446
10.3 Nature of an Earth Electrode System 449 10.4 Earth Conductor Sizes 452
10.5 Design of Earthing Electrodes 454 10.6 System Earthing 458
10.7 Earth Testing 472
Problems 476 Bibliography 477
11. Overhead Lines
11.1 Choice of the System 4 79
11.2 Optimum Design Considerations 481 11.3 Overhead Lines 482
11.4 Design of Overhead Power Lines 488 11.5 Overhead Line Construction 502 11.6 Vibrations 506
11.7 line Accessories 507
11.8 Installation of Distribution Transformer 516 11.9 Compact Lines 575
11.10 Aerial Bunched Cables (ABC) System 520 11.11 Service Line 521
Problems 522 Bibliography 522
12. Underground Cables
12.1 Circuit Design: Key to Reliability [6] 524 12.2 Determination of Cable Rating 536 12.3 Stress Grading 540
444
479
X I I Contents
12 A Thermo-Mechanical Effects in Cable Systems 541
12.5 Cable Materials 542 12.6 Cable Jointing 544 12.7 Installation of Cables 546
12.8 Principal Causes of Cable Failure 553 12.9 Selection of Cables 554
12.10 System Fault Location 556" Problems 562
Bibliography 563
13. System Overvoltages 564
13.1 Causes of Overvoltages 56413.2 Lightning 566
13.3 Protective Devices 569
13.4 Failure of Lightning Arresters 577
13.5 Detection of Arrester Failures in the Field 580 13.6 Allowable Maximum Distance of Separation 557
13.7 Travelling Waves 583 \ 13.8 Protection Schemes 585
13.9 Pole-Mounted Distribution Transformers 588 13.10 Cable Junction 589
13.11 Lightning Arresters: Earthing 590 Problems 592
Bibliography 592
14. Rural Supply 594
14.1 Rural System 59614.2 Reliability 601
14.3 Faults and Protection 602
14 A Improvement of Existing Distribution Systems 6*05
14.5 Single Wire Earth Return System 609 14.6 Fault Locating 610
14.7 Auto-Reclosers 672
14.8 Determination of Rating of Induction Motor (Cage Type) 613
14.9 Constructional Practices 616
14.10 Future Orientation of Rural System 629 Problems 643
Contents
xiii
15. Power Capacitors 646
15.1 Reactive Power 64615.2 Series and Shunt Capacitors 654 15.3 System Harmonics 665
, 15.4 HT Shunt Capacitors' Installation Requirements 6"67 15.5 Size of Capacitors for Power Factor Improvement 671 15.6 LT Capacitors 672
15.7 Construction Features 679 15.8 Failures [7, 6] 680
Problems 682 Bibliography 683
16. Insulation Measurements 685
16.1 Insulation Supervision 68516.2 Insulation Measurement-Non-Destructive Techniques [9] 686 16.3 Insulation Testing: Destructive Tests 697
16.4 Transformer Oil Testing 699 Problems 706
Bibliography 706
17. System Protection 708
17.1 Time Current Characteristics 70817.2 Fuses 709
17.3 Switching Devices 717
17A Circuit Breakers 720
17.5 Protective Relaying 729 17.6 Instrument Transformers 742
• 17.7 Overcurrent Schemes 746
17.8 Unit Protection 748 Problems 749 Bibliography 750
if* System Maintenance * 751
B.I Successful Maintenance 75116.2 Failures and Maintenance 757 18.3 Porcelain Insulators 764
18.4 Transformer Oil Maintenance 765 18.5 Transformer Drying 769
Contents
18.6 Maintenance Staff and Tools 772 18.7 Maintenance Costs 776
Problems 777 Bibliography 777
19. Electrical Services 779
19.1 Standards 779
19.2 Electrical Installations 779 19.3 Reception of Electric Supply 780 19.4 Supply Voltage 783
19.5 Consumer Supply Arrangement 785 19.6 Internal Wiring 790
19.7 Switchgear 796
19.8 Plug and Socket Outlets 798 19.9 Circuit Loading 798
19.10 Load Estimation 804 19.11 Earthing 506 19.12 Lighting 809 19.13 Lamps 570 19.14 Luminaires 572 19.15 Lighting Design 812 19.16 Road Lighting 814 19.17 Floodlighting 819
19.18 Automatic Fire Alarm System 527 19.19 Electrical Call Bell Services 824 19.20 Other Services 824
19.21 Lightning Protection 527 19.22 Standby Supplies 830 19.23 Voltage Stabilizers [5] 537
Problems 833 Bibliography 834
Appendix I: International Electricity Supplies 836 Appendix II: Conductors and Cable Data 841 Appendix III: Power Cable Laying Merits 852
Appendix IV: Village Electrification and Pumpset Energization 854 Appendix V: Electrical Accidents 856
Appendix VI: Illumination Levels 859
Appendix VII: Optimum Specific Energy Consumption 863 Appendix VIII: Tinned Copper Fuse Wire 865
Contents XV Appendix IX: Power Factors 867
Appendix X: Ambient Temperature and Average Altitude 869 Appendix XI: Transmission and Distribution Losses in States 577
