The continuity and quality of electricity delivered safely and economically by today's and future's electrical power networks are important for both developed and developing economies. The correct modelling of power system equipment and correct fault analysis of electrical networks are pre-requisite to ensuring safety and they play a critical role in the identification of economic network investments. Environmental and economic factors require engineers to maximise the use of existing assets which in turn require accurate modelling and analysis techniques. The technology described in this book will always be required for the safe and economic design and operation of electrical power systems.
The book describes relevant advances in industry such as in the areas of international standards developments, emerging new generation technologies such as wind turbine generators, fault current limiters, multi-phase fault analysis, measurement of equipment parameters, probabilistic short-circuit analysis and electrical interference.
*A fully up-to-date guide to the analysis and practical troubleshooting of short-circuit faults in electricity utilities and industrial power systems
*Covers generators, transformers, substations, overhead power lines and industrial systems with a focus on best-practice techniques, safety issues, power system planning and economics.
*North American and British / European standards covered
This book provides a comprehensive practical treatment of the modelling of electrical power systems, and the theory and practice of fault analysis of power systems covering detailed and advanced theories as well as modern industry practices.The continuity and quality of electricity delivered safely and economically by today's and future's electrical power networks are important for both developed and developing economies. The correct modelling of power system equipment and correct fault analysis of electrical networks are pre-requisite to ensuring safety and they play a critical role in the identification of economic network investments. Environmental and economic factors require engineers to maximise the use of existing assets which in turn require accurate modelling and analysis techniques. The technology described in this book will always be required for the safe and economic design and operation of electrical power systems. The book describes relevant advances in industry such as in the areas of international standards developments, emerging new generation technologies such as wind turbine generators, fault current limiters, multi-phase fault analysis, measurement of equipment parameters, probabilistic short-circuit analysis and electrical interference.*A fully up-to-date guide to the analysis and practical troubleshooting of short-circuit faults in electricity utilities and industrial power systems*Covers generators, transformers, substations, overhead power lines and industrial systems with a focus on best-practice techniques, safety issues, power system planning and economics*North American and British / European standards covered
Front cover 1
Power systems modelling and fault analysis 4
Copyright page 5
Contents 8
List of electrical symbols 18
Foreword 20
Preface 22
Biography 25
Chapter 1 Introduction to power system faults 26
1.1 General 26
1.2 Structure of power systems 26
1.3 Need for power system fault analysis 27
1.3.1 General 27
1.3.2 Health and safety considerations 28
1.3.3 Design, operation and protection of power systems 28
1.3.4 Design of power system equipment 29
1.4 Characteristics of power system faults 29
1.4.1 Nature of faults 29
1.4.2 Types of faults 29
1.4.3 Causes of faults 30
1.4.4 Characterisation of faults 31
1.5 Terminology of short-circuit current waveform and current interruption 33
1.6 Effects of short-circuit currents on equipment 37
1.6.1 Thermal effects 37
1.6.2 Mechanical effects 37
1.7 Per-unit analysis of power systems 40
1.7.1 General 40
1.7.2 Single-phase systems 40
1.7.3 Change of base quantities 43
1.7.4 Three-phase systems 44
1.7.5 Mutually coupled systems having different operating voltages 45
1.7.6 Examples 50
Chapter 2 Theory of symmetrical components and connection of phase sequence networks during faults 53
2.1 General 53
2.2 Symmetrical components of a three-phase power system 54
2.2.1 Balanced three-phase voltage and current phasors 54
2.2.2 Symmetrical components of unbalanced voltage or current phasors 56
2.2.3 Apparent power in symmetrical component terms 59
2.2.4 Definition of phase sequence component networks 59
2.2.5 Sequence components of unbalanced three-phase impedances 61
2.2.6 Sequence components of balanced three-phase impedances 64
2.2.7 Advantages of symmetrical components frame of reference 65
2.2.8 Examples 65
2.3 Analysis of balanced and unbalanced faults in the sequence reference frame 68
2.3.1 General 68
2.3.2 Balanced three-phase to earth short-circuit faults 68
2.3.3 Balanced three-phase clear of earth short-circuit faults 70
2.3.4 Unbalanced one-phase to earth short-circuit faults 72
2.3.5 Unbalanced phase-to-phase or two-phase short-circuit faults 74
2.3.6 Unbalanced two-phase to earth short-circuit faults 76
2.3.7 Unbalanced one-phase open-circuit faults 80
2.3.8 Unbalanced two-phase open-circuit faults 81
2.3.9 Example 83
2.4 Fault analysis and choice of reference frame 84
2.4.1 General 84
2.4.2 One-phase to earth short-circuit faults 85
2.4.3 Two-phase to earth short-circuit faults 86
2.5 Analysis of simultaneous faults 88
2.5.1 General 88
2.5.2 Simultaneous short-circuit faults at the same location 88
2.5.3 Cross-country faults or simultaneous faults at different locations 90
2.5.4 Simultaneous open-circuit and short-circuit faults at the same location 91
2.5.5 Simultaneous faults caused by broken and fallen to earth conductors 93
2.5.6 Simultaneous short-circuit and open-circuit faults on distribution transformers 94
Further reading 98
Chapter 3 Modelling of multi-conductor overhead lines and cables 99
3.1 General 99
3.2 Phase and sequence modelling of three-phase overhead lines 99
3.2.1 Background 99
3.2.2 Overview of the calculation of overhead line parameters 101
3.2.3 Untransposed single-circuit three-phase lines with and without earth wires 114
3.2.4 Transposition of single-circuit three-phase lines 121
3.2.5 Untransposed double-circuit lines with earth wires 127
3.2.6 Transposition of double-circuit overhead lines 133
3.2.7 Untransposed and transposed multiple-circuit lines 148
3.2.8 Examples 152
3.3 Phase and sequence modelling of three-phase cables 165
3.3.1 Background 165
3.3.2 Cable sheath bonding and earthing arrangements 167
3.3.3 Overview of the calculation of cable parameters 170
3.3.4 Series phase and sequence impedance matrices of single-circuit cables 179
3.3.5 Shunt phase and sequence susceptance matrices of single-circuit cables 189
3.3.6 Three-phase double-circuit cables 193
3.3.7 Examples 195
3.4 Sequence & #960
3.4.1 Background 198
3.4.2 Sequence & #960
3.4.3 Sequence & #960
3.4.4 Sequence & #960
3.5 Sequence & #960
3.6 Three-phase modelling of overhead lines and cables (phase frame of reference) 207
3.6.1 Background 207
3.6.2 Single-circuit overhead lines and cables 208
3.6.3 Double-circuit overhead lines and cables 209
3.7 Computer calculations and measurements of overhead line and cable parameters 211
3.7.1 Computer calculations of overhead line and cable parameters 211
3.7.2 Measurement of overhead line parameters 212
3.7.3 Measurement of cable parameters 218
3.8 Practical aspects of phase and sequence parameters of overhead lines and cables 222
3.8.1 Overhead lines 222
3.8.2 Cables 222
Further reading 223
Chapter 4 Modelling of transformers, static power plant and static load 225
4.1 General 225
4.2 Sequence modelling of transformers 225
4.2.1 Background 225
4.2.2 Single-phase two-winding transformers 227
4.2.3 Three-phase two-winding transformers 238
4.2.4 Three-phase three-winding transformers 249
4.2.5 Three-phase autotransformers with and without tertiary windings 255
4.2.6 Three-phase earthing or zig-zag transformers 267
4.2.7 Single-phase traction transformers connected to three-phase systems 268
4.2.8 Variation of transformer's PPS leakage impedance with tap position 270
4.2.9 Practical aspects of ZPS impedances of transformers 271
4.2.10 Measurement of sequence impedances of three-phase transformers 274
4.2.11 Examples 279
4.3 Sequence modelling of QBs and PS transformers 286
4.3.1 Background 286
4.3.2 PPS, NPS and ZPS modelling of QBs and PSs 288
4.3.3 Measurement of QB and PS sequence impedances 293
4.4 Sequence modelling of series and shunt reactors and capacitors 297
4.4.1 Background 297
4.4.2 Modelling of series reactors 298
4.4.3 Modelling of shunt reactors and capacitors 300
4.4.4 Modelling of series capacitors 303
4.5 Sequence modelling of static variable compensators 308
4.5.1 Background 308
4.5.2 PPS, NPS and ZPS modelling 309
4.6 Sequence modelling of static power system load 310
4.6.1 Background 310
4.6.2 PPS, NPS and ZPS modelling 311
4.7 Three-phase modelling of static power plant and load in the phase frame of reference 311
4.7.1 Background 311
4.7.2 Three-phase modelling of reactors and capacitors 311
4.7.3 Three-phase modelling of transformers 312
4.7.4 Three-phase modelling of QBs and PSs 322
4.7.5 Three-phase modelling of static load 324
Further reading 325
Chapter 5 Modelling of ac rotating machines 326
5.1 General 326
5.2 Overview of synchronous machine modelling in the phase frame of reference 327
5.3 Synchronous machine modelling in the dq0 frame of reference 329
5.3.1 Transformation from phase ryb to dq0 frame of reference 329
5.3.2 Machine dq0 equations in per unit 331
5.3.3 Machine operator reactance analysis 333
5.3.4 Machine parameters: subtransient and transient reactances and time constants 335
5.4 Synchronous machine behaviour under short-circuit faults and modelling in the sequence reference frame 339
5.4.1 Synchronous machine sequence equivalent circuits 339
5.4.2 Three-phase short-circuit faults 340
5.4.3 Unbalanced two-phase (phase-to-phase) short-circuit faults 349
5.4.4 Unbalanced single-phase to earth short-circuit faults 353
5.4.5 Unbalanced two-phase to earth short-circuit faults 357
5.4.6 Modelling the effect of initial machine loading 362
5.4.7 Effect of AVRs on short-circuit currents 364
5.4.8 Modelling of synchronous motors/compensators/condensers 367
5.4.9 Examples 368
5.5 Determination of synchronous machines parameters from measurements 373
5.5.1 Measurement of PPS reactances, PPS resistance and d-axis short-circuit time constants 373
5.5.2 Measurement of NPS impedance 377
5.5.3 Measurement of ZPS impedance 378
5.5.4 Example 378
5.6 Modelling of induction motors in the phase frame of reference 382
5.6.1 General 382
5.6.2 Overview of induction motor modelling in the phase frame of reference 383
5.7 Modelling of induction motors in the dq frame of reference 387
5.7.1 Transformation to dq axes 387
5.7.2 Complex form of induction motor equations 388
5.7.3 Operator reactance and parameters of a single-winding rotor 388
5.7.4 Operator reactance and parameters of double-cage or deep-bar rotor 389
5.8 Induction motor behaviour under short-circuit faults and modelling in the sequence reference frame 393
5.8.1 Three-phase short-circuit faults 393
5.8.2 Unbalanced single-phase to earth short-circuit faults 400
5.8.3 Modelling the effect of initial motor loading 402
5.8.4 Determination of motor's electrical parameters from tests 403
5.8.5 Examples 408
5.9 Modelling of wind turbine generators in short-circuit analysis 410
5.9.1 Types of wind turbine generator technologies 410
5.9.2 Modelling of fixed speed induction generators 413
5.9.3 Modelling of small speed range wound rotor induction generators 413
5.9.4 Modelling of doubly fed induction generators 414
5.9.5 Modelling of series converter-connected generators 418
Further reading 421
Chapter 6 Short-circuit analysis techniques in ac power systems 422
6.1 General 422
6.2 Application of Thévenin's and superposition's theorems to the simulation of short-circuit and open-circuit faults 423
6.2.1 Simulation of short-circuit faults 423
6.2.2 Simulation of open-circuit faults 425
6.3 Fixed impedance short-circuit analysis techniques 427
6.3.1 Background 427
6.3.2 Passive short-circuit analysis techniques 427
6.3.3 The ac short-circuit analysis techniques 428
6.3.4 Estimation of dc short-circuit current component variation with time 428
6.3.5 Estimation of ac short-circuit current component variation with time 429
6.4 Time domain short-circuit analysis techniques in large-scale power systems 429
6.5 Analysis of the time variation of ac and dc short-circuit current components 430
6.5.1 Single short-circuit source connected by a radial network 430
6.5.2 Parallel independent short-circuit sources connected by radial networks 433
6.5.3 Multiple short-circuit sources in interconnected networks 437
6.6 Fixed impedance short-circuit analysis of large-scale power systems 442
6.6.1 Background 442
6.6.2 General analysis of balanced three-phase short-circuit faults 442
6.6.3 General analysis of unbalanced short-circuit faults 453
6.6.4 General analysis of open-circuit faults 460
6.7 Three-phase short-circuit analysis of large-scale power systems in the phase frame of reference 463
6.7.1 Background 463
6.7.2 Three-phase models of synchronous and induction machines 463
6.7.3 Three-phase analysis of ac current in the phase frame of reference 466
6.7.4 Three-phase analysis and estimation of X/R ratio of fault current 470
6.7.5 Example 473
Further reading 475
Chapter 7 International standards for short-circuit analysis in ac power systems 476
7.1 General 476
7.2 International Electro-technical Commission 60909-0 Standard 476
7.2.1 Background 476
7.2.2 Analysis technique and voltage source at the short-circuit location 477
7.2.3 Impedance correction factors 478
7.2.4 Asynchronous motors and static converter drives 481
7.2.5 Calculated short-circuit currents 483
7.2.6 Example 487
7.3 UK Engineering Recommendation ER G7/4 488
7.3.1 Background 488
7.3.2 Representation of machines and passive load 489
7.3.3 Analysis technique 490
7.3.4 Calculated short-circuit currents 491
7.3.5 Implementation of ER G7/4 in the UK 492
7.4 American IEEE C37.010 Standard 494
7.4.1 Background 494
7.4.2 Representation of system and equipment 494
7.4.3 Analysis technique 495
7.4.4 Calculated short-circuit currents 496
7.5 Example calculations using IEC 60909, UK ER G7/4 and IEEE C37.010 498
7.6 IEC 62271-100-2001 and IEEE C37.04-1999 circuit-breaker standards 504
7.6.1 Short-circuit ratings 504
7.6.2 Assessment of circuit-breakers short-circuit duties against ratings 506
Further reading 508
Chapter 8 Network equivalents and practical short-circuit current assessments in large-scale ac power systems 510
8.1 General 510
8.2 Power system equivalents for large-scale system studies 510
8.2.1 Theory of static network reduction 510
8.2.2 Need for power system equivalents 512
8.2.3 Mathematical derivation of power system equivalents 514
8.3 Representation of power systems in large-scale studies 521
8.3.1 Representation of power generating stations 521
8.3.2 Representation of transmission, distribution and industrial networks 522
8.4 Practical analysis to maximise short-circuit current predictions 523
8.4.1 Superposition analysis and initial ac loadflow operating conditions 523
8.4.2 Effect of mutual coupling between overhead line circuits 524
8.4.3 Severity of fault types and substation configuration 526
8.5 Uncertainties in short-circuit current calculations: precision versus accuracy 528
8.6 Probabilistic short-circuit analysis 532
8.6.1 Background 532
8.6.2 Probabilistic analysis of ac short-circuit current component 532
8.6.3 Probabilistic analysis of dc short-circuit current component 534
8.6.4 Example 540
8.7 Risk assessment and safety considerations 541
8.7.1 Background 541
8.7.2 Relevant UK legislation 542
8.7.3 Theory of quantified risk assessment 542
8.7.4 Methodology of quantified risk assessment 543
Further reading 544
Chapter 9 Control and limitation of high short-circuit currents 545
9.1 General 545
9.2 Limitation of short-circuit currents in power system operation 545
9.2.1 Background 545
9.2.2 Re-certification of existing plant short-circuit rating 546
9.2.3 Substation splitting and use of circuit-breaker autoclosing 546
9.2.4 Network splitting and reduced system parallelism 548
9.2.5 Sequential disconnection of healthy then faulted equipment 549
9.2.6 Increasing short-circuit fault clearance time 549
9.2.7 De-loading circuits 550
9.2.8 Last resort generation disconnection 550
9.2.9 Example 550
9.3 Limitation of short-circuit currents in power system design and planning 552
9.3.1 Background 552
9.3.2 Opening of unloaded delta-connected transformer tertiary windings 552
9.3.3 Specifying higher leakage impedance for new transformers 553
9.3.4 Upgrading to higher nominal system voltage levels 553
9.3.5 Uprating and replacement of switchgear and other substation equipment 554
9.3.6 Wholesale replacement of switchgear and other substation equipment 554
9.3.7 Use of short-circuit fault current limiters 554
9.3.8 Examples 554
9.4 Types of short-circuit fault current limiters 556
9.4.1 Background 556
9.4.2 Earthing resistor or reactor connected to transformer neutral 556
9.4.3 Pyrotechnic-based fault current limiters 557
9.4.4 Permanently inserted current limiting series reactor 558
9.4.5 Series resonant current limiters using a bypass switch 559
9.4.6 Limiters using magnetically coupled circuits 559
9.4.7 Saturable reactor limiters 561
9.4.8 Passive damped resonant limiter 561
9.4.9 Solid state limiters using power electronic switches 563
9.4.10 Superconducting fault current limiters 564
9.4.11 The ideal fault current limiter 568
9.4.12 Applications of fault current limiters 568
9.4.13 Examples 571
Further reading 574
Chapter 10 An introduction to the analysis of short-circuit earth return current, rise of earth potential and electrical interference 575
10.1 Background 575
10.2 Electric shock and tolerance of the human body to ac currents 576
10.2.1 Step, touch, mesh and transferred potentials 576
10.2.2 Electrical resistance of the human body 577
10.2.3 Effects of ac current on the human body 578
10.3 Substation earth electrode system 580
10.3.1 Functions of substation earth electrode system 580
10.3.2 Equivalent resistance to remote earth 580
10.4 Overhead line earthing network 586
10.4.1 Overhead line earth wire and towers earthing network 586
10.4.2 Equivalent earthing network impedance of an infinite overhead line 586
10.5 Analysis of earth fault ZPS current distribution in overhead line earth wire, towers and in earth 588
10.6 Cable earthing system impedance 592
10.7 Overall substation earthing system and its equivalent impedance 592
10.8 Effect of system earthing methods on earth fault current magnitude 593
10.9 Screening factors for overhead lines 594
10.10 Screening factors for cables 596
10.10.1 General 596
10.10.2 Single-phase cable with metallic sheath 596
10.10.3 Three-phase cable with metallic sheaths 598
10.11 Analysis of earth return currents for short-circuits in substations 601
10.12 Analysis of earth return currents for short circuits on overhead line towers 602
10.13 Calculation of rise of earth potential 604
10.14 Examples 605
10.15 Electrical interference from overhead power lines to metal pipelines 609
10.15.1 Background 609
10.15.2 Electrostatic or capacitive coupling from power lines to pipelines 610
10.15.3 Electromagnetic or inductive coupling from power lines to pipelines 613
10.15.4 Resistive or conductive coupling from power systems to pipelines 620
10.15.5 Examples 620
Further reading 628
Appendices 630
A.1 Theory and analysis of distributed multi-conductor lines and cables 630
A.2 Typical data of power system equipment 633
A.2.1 General 633
A.2.2 Data 634
Index 644
A 644
B 644
C 644
D 645
E 645
F 646
G 646
H 646
I 646
L 647
M 647
N 647
O 647
P 647
Q 648
R 648
S 648
T 649
U 650
V 650
W 650
X 650
Z 650
1 Introduction to power system faults
1.1 General
In this introductory chapter, we introduce the important terminology of fault current waveform, discuss the need for power system fault analysis and the effects of fault currents in power systems. Per-unit analysis concept of single-phase and three-phase power systems is presented including the base and per-unit equations of self and mutual impedances and admittances.
1.2 Structure of power systems
Electrical ac power systems consist of three-phase generation systems, transmission and distribution networks, and loads. The networks supply large three-phase industrial loads at various distribution and transmission voltages as well as single-phase residential and commercial loads. In some countries, e.g. North America, the term subtransmission is used to denote networks with voltage classes between transmission and distribution. Distribution voltages are typically 10–60 kV, subtransmission voltages are typically 66–138 kV and transmission voltages are typically above 138 kV. Generated voltages are up to 35 kV for generators used in large electrical power stations. Power station auxiliary supply systems and industrial power systems supply a significant amount of induction motor load. Residential and commercial loads include a significant amount of single-phase induction motor loads.
For over a century, electric power systems used synchronous machines for the generation of electricity. However, in the twenty-first century, the generation of electricity from renewable energy sources such as wind has begun to expand at a large pace. Generally, such generation systems use a variety of asynchronous machines as well as machines interfaced to the three-phase network through a low voltage direct current link or a power electronics converter. Typical ratings of wind turbine generators are currently up to 5 MW and typical generated voltage range from 0.4 to 5 kV. The mix of synchronous, asynchronous and converter isolated electrical generation systems is expected to change the behaviour of three-phase power systems following disturbances such as short-circuit faults. Figure 1.1 illustrates a typical structure and components of a generation, transmission and distribution power system and Figure 1.2 illustrates a typical auxiliary electrical supply system for a large power station representing box A in Figure 1.1.
Figure 1.1 Typical structure and components of a generation, transmission and distribution power system
Figure 1.2 Typical structure and components of a power station auxiliary electrical supply system
1.3 Need for power system fault analysis
1.3.1 General
Short-circuit analysis is carried out in electrical power utility systems, industrial power systems, commercial power systems and power station auxiliary systems. Other special applications are in concentrated power system installations on board military and commercial ships and aircraft. Short-circuit calculations are generally performed for a number of reasons. These are briefly described in the next sections.
1.3.2 Health and safety considerations
Short-circuit fault analysis is carried out to ensure the safety of workers as well as the general public. Power system equipment such as circuit-breakers can fail catastrophically if they are subjected to fault duties that exceed their rating. Other equipment such as busbars, transformers and cables can fail thermally or mechanically if subjected to fault currents in excess of ratings. In addition, to ensure safety, short-circuit fault analysis is carried out and used in the calculation of rise of earth potential at substations and overhead line towers. Other areas where fault analysis is carried out are for the calculation of induced voltages on adjacent communication circuits, pipelines, fences and other metallic objects.
1.3.3 Design, operation and protection of power systems
Short-circuit current calculations are made at the system design stage to determine the short-circuit ratings of new switchgear and substation infrastructure equipment to be procured and installed. System reinforcements may be triggered by network expansion and/or the connection of new generating plant to the power system. Routine calculations are also made to check the continued adequacy of existing equipment as system operating configurations are modified. In addition, calculations of minimum short-circuit currents are made and these are used in the calculation of protection relay settings to ensure accurate and coordinated relay operations. In transmission systems, short-circuit currents must be quickly cleared to avoid loss of synchronism of generation plant and major power system blackouts. Maximum short-circuit current calculations are carried out for the design of substation earth electrode systems. Short-circuit analysis is also carried out as part of initial power quality assessments for the connection of disturbing loads to electrical power networks. These assessments include voltage flicker, harmonic analysis and voltage unbalance. Other areas where short-circuit analysis is carried out is in the modification of an existing system or at the design stage of new electrical power installations such as a new offshore oil platform, new petrochemical process plant or the auxiliary electrical power system of a new power station. The aim is to determine the short-circuit rating of new switchgear and other substation infrastructure equipment that will be procured and installed.
1.3.4 Design of power system equipment
Switchgear manufacturers design their circuit-breakers to ensure that they are capable of making, breaking and carrying, for a short time, the specified short-circuit current. Equipment with standardised short-circuit ratings are designed and produced by manufacturers. Also, manufacturers of substation infrastructure equipment and other power system plant, e.g. transformers and cables, use the short-circuit current ratings specified by their customers to ensure that the equipment is designed to safely withstand the passage of these currents for the duration specified.
1.4 Characteristics of power system faults
1.4.1 Nature of faults
A fault on a power system is an abnormal condition that involves an electrical failure of power system equipment operating at one of the primary voltages within the system. Generally, two types of failure can occur. The first is an insulation failure that results in a short-circuit fault and can occur as a result of overstressing and degradation of the insulation over time or due to a sudden overvoltage condition. The second is a failure that results in a cessation of current flow or an open-circuit fault.
1.4.2 Types of faults
Short-circuit faults can occur between phases, or between phases and earth, or both. Short circuits may be one-phase to earth, phase to phase, two-phase to earth, three-phase clear of earth and three-phase to earth. The three-phase fault that symmetrically affects the three phases of a three-phase circuit is the only balanced fault whereas all the other faults are unbalanced. Simultaneous faults are a combination of two or more faults that occur at the same time. They may be of the same or different types and may occur at the same or at different locations. A broken overhead line conductor that falls to earth is a simultaneous one-phase open-circuit and one-phase short-circuit fault at one location. A short-circuit fault occurring at the same time on each circuit of a double-circuit overhead line, where the two circuits are strung on the same tower, is a simultaneous fault condition. A one-phase to earth short-circuit fault in a high impedance earthed distribution system may cause a sufficient voltage rise on a healthy phase elsewhere in the system that a flashover and short-circuit fault occurs. This is known as a cross-country fault. Most faults do not change in type during the fault period but some faults do change and evolve from say a one-phase to earth short circuit to engulf a second phase where it changes to a two-phase to earth short circuit fault. This can occur on overhead lines or in substations where the flashover arc of the faulted phase spreads to other healthy phases. Internal short circuits to earth and open-circuit faults can also occur on windings of transformers, reactors and machines as well as faults between a number of winding turns of the same phase.
1.4.3 Causes of faults
Open-circuit faults may be caused by the failure of joints on cables or overhead lines or the failure of all the three phases of a circuit-breaker or disconnector to open or close. For example, two phases of a circuit-breaker may close and latch but not the third phase or two phases may properly open but the third remains stuck in the closed position. Except on mainly underground systems, the vast majority of short-circuit faults are weather related followed by equipment failure. The weather factors that usually cause short-circuit faults are: lightning strikes, accumulation of snow or ice, heavy rain, strong winds or gales, salt pollution depositing on insulators on overhead lines and...
| Erscheint lt. Verlag | 30.11.2007 |
|---|---|
| Sprache | englisch |
| Themenwelt | Sachbuch/Ratgeber |
| Technik ► Elektrotechnik / Energietechnik | |
| Technik ► Maschinenbau | |
| ISBN-10 | 0-08-055427-X / 008055427X |
| ISBN-13 | 978-0-08-055427-3 / 9780080554273 |
| Haben Sie eine Frage zum Produkt? |
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