Preface
Continuous change in protective relaying has been caused by two different influences. One is the fact that the requirements imposed by power systems are in a constant state of change, and our understanding of the basic concepts has sharpened considerably over the years. The other is that the means of implementing the fundamental concepts of fault location and removal and system restoration are constantly growing more sophisticated. It is primarily because of these changing constraints that this text has been revised and expanded. It began with contributions from two giants of the industry, J. Lewis Blackburn and George D. Rockefeller. From the nucleus of their extensive analyses and writings, and the desire to cover each new contingency with new relaying concepts, this volume has evolved. New solutions to age-old problems have become apparent as greater experience has been gained. No problem is without benefit in the solution found. This new edition weeds out those relaying concepts that have run their course and have been replaced by more perceptive methods of implementation using new solid-state or microprocessor-based devices. No single technological breakthrough has been more influential in generating change than the microprocessor. Initia Initially lly,, the method methodss of transl translati ating ng a collec collectio tion n of instan instantan taneou eouss sample sampless of sine sine waves waves into into useful useful curren current, t, direction, and impedance measurements were not obvious. Diligent analysis and extensive testing allowed these useful functions to be obtained and to be applied to the desired protective functions. This text attempts to describe, in the simplest possible terms, the manner in which these digital measurements are accomplished in present-day devices. In addition to those already mentioned, huge contributions were made in the development and refinement of the concepts described in this book by Hung Jen Li, Walter Hinman, Roger Ray, James Crockett, Herb Lensner, Al Regott Regotti, i, Fernan Fernando do Calero Calero,, Eric Eric Udren, Udren, James James Greene Greene,, Lianch Liancheng eng Wang, Wang, Elmo Elmo Price, Price, Solvei Solveig g Ward, Ward, John John McGowan, and Cliff Downs. Some of these names may not be immediately recognizable, but all have made an impact with their thoughtful, accurate, well-reasoned writings, and they all deserve the gratitude of the industry for the wealth of knowledge they have contributed to this book. I am keenly aware of the high quality of the technical offerings of these people, and I am particularly grateful for the warmth and depth of their friendship. Walter A. Elmore
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Contents
Preface
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1 Introduction and General Philosophies Revised by W. A. Elmore
1
1 Introduction 2 Classification of Relays 2.1 Analog/Digital/Numerical 3 Protective Relaying Systems and Their Design 3.1 Design Criteria 3.2 Factors Influencing Relay Performance 3.3 Zones of Protection 4 Applying Protective Relays 4.1 System Configuration 4.2 Existing System Protection and Procedures 4.3 Degree of Protection Required 4.4 Fault Study 4.5 Maximum Loads, Transformer Data, and Impedances 5 Relays and Application Data 5.1 Switchboard Relays 5.2 Rack-Mounted Relays 6 Circuit-Breaker Control 7 Comparison of Symbols 2 Tech Techn nical ical Tool Toolss of the Relay elay Engi Engine neer er:: Phas Phasor ors, s, Pol Polarit arity y, and and Symme ymmettrica ricall Compo ompon nents ents Revised by W. A. Elmore
1 Introduction 2 Phasors 2.1 Circuit Diagram Notation for Current and Flux 2.2 Circuit Diagram Notation for Voltage
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1 1 2 2 3 4 4 4 5 5 5 5 6 6 6 7 8 9 11
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Chapter 1
also have a higher initial cost. The higher performance and cost cannot always be justified. Consequently, both low- and high-speed relays are used to protect power systems. Both types have high reliability records. Records on protective relay operations consistently show 99.5% and better relay performance.
3.1.4 Simplicity As in any other engineering discipline, simplicity in a protective relay system is always the hallmark of good design. The simplest relay system, however, is not always the most economical. As previously indicated, major economies may be possible with a complex relay system that uses a minimum number of circuit breakers. Other factors being equal, simplicity of design improves system reliability—if only because there are fewer elements that can malfunction.
3.2 Factors Influencing Relay Performance Relay performance is generally classed as (1) correct, (2) no conclusion, or (3) incorrect. Incorrect operation may be either failure to trip or false tripping. The cause of incorrect operation may be (1) poor application, (2) incorrect settings, (3) personnel error, or (4) equipment malfunction. Equipment that can cause an incorrect operation includes current transformers, voltage transformers, breakers, cable and wiring, relays, channels, or station batteries. Incorrect tripping of circuit breakers not associated with the trouble area is often as disastrous as a failure to trip. Hence, special care must be taken in both application and installation to ensure against this. ‘‘No conclusion’’ is the last resort when no evidence is available for a correct or incorrect operation. Quite often this is a personnel involvement.
3.3 Zones of Protection The general philosophy of relay applications is to divide the power system into zones that can be protected adequately with fault recognition and removal producing disconnection of a minimum amount of the system. The power system is divided into protective zones for 1. Generators 2. Transformers 3. Buses
Figure 1-1 A typical system and its zones of protection.
4. Transmission and distribution circuits 5. Motors A typical power system and its zones of protection are shown in Figure 1-1. The location of the current transformers supplying the relay or relay system defines the edge of the protective zone. The purpose of the protective system is to provide the first line of protection within the guidelines outlined above. Since failures do occur, however, some form of backup protection is provided to trip out the adjacent breakers or zones surrounding the trouble area. Protection in each zone is overlapped to avoid the possibility of unprotected areas. This overlap is accomplished by connecting the relays to current transformers, as shown in Figure 1-2a. It shows the connection for ‘‘dead tank’’ breakers, and Figure 1-2b the ‘‘live tank’’ breakers commonly used with EHV circuits. Any trouble in the small area between the current transformers will operate both zone A and B relays and trip all breakers in the two zones. In Figure 1-2a, this small area represents the breaker, and in Figure 1-2b the current transformer, which is generally not part of the breaker.
4 APPLYING PROTECTIVE RELAYS The first step in applying protective relays is to state the protection problem accurately. Although developing a clear, accurate statement of the problem can often be the most difficult part, the time spent will pay dividends—particularly when assistance from others is
Contents
4 Protection Against Transients and Surges
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W. A. Elmore
1 Introduction 1.1 Electrostatic Induction 1.2 Electromagnetic Induction 1.3 Differential- and Common-Mode Classifications 2 Transients Originating in the High-Voltage System 2 .1 Capacitor Switching 2 .2 Bus Deenergization 2.3 Transmission Line Switching 2.4 C Co oupling Capacitor Voltage Transformer (CCVT) Switching 2 .5 Other Transient Sources 3 Transients Originating in the Low-Voltage System 3.1 Direct Current Coil Interruption 3.2 Direct Current Circuit Energization 3.3 Current Transformer Saturation 3.4 Grounding of Battery Circuit 4 Protective Measures 4 .1 Separation 4.2 Suppression at the Source 4.3 Suppression by Shielding 4 .4 Suppression by Twisting 4.5 Radial Routing of Control Cables 4 .6 Buffers 4 .7 Optical Isolators 4.8 Increased Energy Requirement 5 Instrument Transformers for Relaying
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W. A. Elmore
1 Introduction 2 Current Transformers 2.1 Saturation 2.2 Effect of dc Component 3 Equivalent Circuit 4 Estimation of Current Transformer Performance 4.1 Formula Method 4.2 Excitation Curve Method 4.3 ANSI Standard: Current Transformer Accuracy Classes 5 European Practice 5.1 TPX 5.2 TPY 5.3 TPZ 6 Direct Current Saturation 7 Residual Flux 8 MOCT 9 Voltage Transformers and Coupling Capacitance Voltage Transformers 9.1 Equivalent Circuit of a Voltage Transformer 9.2 Coupling Capacitor Voltage Transformers 9.3 MOVT/EOVT 10 Neutral Inversion
81 81 81 82 82 82 83 83 85 87 88 88 88 88 89 91 91 91 92 93 93
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Contents
6 Microprocessor Relaying Fundamentals W. A. Elmore
1 2 3 4
Introduction Sampling Problems Aliasing How to Overcome Aliasing 4.1 Antialiasing Filters 4.2 Nonsynchronous Sampling 5 Choice of Measurement Principle 5.1 rms Calculation 5.2 Digital Filters 5.3 Fourier-Notch Filter 5.4 Another Digital Filter 5.5 dc Offset Compensation 5.6 Symmetrical Component Filter 5.7 Leading-Phase Identification 5.8 Fault Detectors 6 Self-Testing 6.1 Dead-Man Timer 6.2 Analog Test 6.3 Check-Sum 6.4 RAM Test 6.5 Nonvolatile Memory Test 7 Conclusions 7 System Grounding and Protective Relaying Revised by W. A. Elmore
1 Introduction 2 Ungrounded Systems 2.1 Ground Faults on Ungrounded Systems 2.2 Ground Fault Detection on Ungrounded Systems 3 Reactance Grounding 3.1 High-Reactance Grounding 3.2 Resonant Grounding (Ground Fault Neutralizer) 3.3 Low-Reactance Grounding 4 Resistance Grounding 4.1 Low-Resistance Grounding 4.2 High-Resistance Grounding 5 Sensitive Ground Relaying 5.1 Ground Overcurrent Relay with Conventional Current Transformers 5.2 Ground Product Relay with Conventional Current Transformers 5.3 Ground Overcurrent Relay with Zero Sequence Current Transformers 6 Ground Fault Protection for Three-Phase, Four-Wire Systems 6.1 Unigrounded Four-Wire Systems 6.2 Multigrounded Four-Wire Systems 8 Generator Protection Revised by C. L. Downs
1 Introduction 2 Choice of Technology
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1 05 105 105 107 108 108 109 1 09 110 110 111 11 2 112 113 114 114 11 4 11 5 117
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Contents
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3 Phase Fault Detection 3.1 Percentage Differential Relays (Device 87) 3.2 High Impedance Differential Relays (Device 87) 3.3 Machine Connections 3.4 Split-Phase 4 Stator Ground Fault Protection 4.1 Unit-Connected Schemes 4.2 95% Ground Relays 4.3 Neutral-to-Ground Fault Detection (Device 87N3) 4.4 100% Winding Protection 5 Backup Protection 5.1 Unbalanced Faults 5.2 Balanced Faults 6 Overload Protection 6.1 RTD Schemes (Device 49) 6.2 Thermal Replicas (Device 49) 7 Volts per Hertz Protection 8 Overspeed Protection 9 Loss-of-Excitation Protection 9.1 Causes of Machine Loss of Field 9.2 Hazard 9.3 Loss-of-Field Relays 9.4 KLF and KLF-1 Curves 9.5 Two-Zone KLF Scheme 10 Protection Against Generator Motoring 10.1 Steam Turbines 10.2 Diesel Engines 10.3 Gas Turbines 10.4 Hydraulic Turbines 11 Inadvertent Energization 12 Field Ground Detection 12.1 Brush-Type Machine 12.2 Brushless Machines 12.3 Injection Scheme for Field Ground Detection 13 Alternating-Current Overvoltage Protection for Hydroelectric Generators 14 Generator Protection at Reduced Frequencies 15 Off-Frequency Operation 16 Recommended Protection 17 Out-of-Step Protection 18 Bus Transfer Systems for Station Auxiliaries 18.1 Fast Transfer 18.2 Choice of Fast Transfer Scheme 18.3 Slow Transfer 19 Microprocessor-Based Generator Protection
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Motor Protection
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Revised by C. L. Downs
1 Introduction 1 .1 General Requirements 1.2 Induction Motor Equivalent Circuit 1.3 Motor Thermal Capability Curves
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Phase-Fault Protection Ground-Fault Protection Locked-Rotor Protection Overload Protection Thermal Relays 6.1 RTD-Input-Type Relays 6.2 Thermal Replica Relays Low-Voltage Protection Phase-Rotation Protection Negative Sequence Voltage Protection Phase-Unbalance Protection Negative Sequence Current Relays Jam Protection Load Loss Protection Out-of-Step Protection Loss of Excitation Typical Application Co
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