Protection of Electricity Distribution Networks (Energy Engineering)

Description

High quality electrical service is key to power systems around the world, particularly in utilities and industrial facilities. Both voltage and grid frequency must be kept within tight limits to maintain functioning of critical infrastructure. The growing use of renewable power of intermittent character is adding to that challenge. One of the keys to achieving quality service is the protection system, which needs to be reliable, fast and with a good cost/benefit ratio. It consists of various components, including relays, circuit breakers and fuses. An understanding of the different behaviours of these components in the face of malfunctions, and of countermeasures, is needed. This book has established itself as a classic work in its field, allowing the reader to easily follow the ideas explored. It provides an overview of most aspects of electrical protections, with emphasis on distribution systems; but protection of generation and transmission systems are also addressed. For this 4th edition, new topics have been added, such as protection of renewable power plants and transient stability analysis. It offers a thorough revision of the material, particularly the numerical type of relays, protective functions, control, measurement, communications and oscillography features. Most chapters have illustrative examples using MATLAB or PSAT (Power System Analysis Tools). This work remains essential reading for researchers, utility engineers, design, maintenance and consulting engineers as well as for instructors and senior students. Title Copyright Contents About the authors Preface and acknowledgements Preface to second edition Preface to third edition Preface to fourth edition 1 Introduction 1.1 General 1.2 Basic principles of electrical systems 1.3 Protection requirements 1.4 Protection zones 1.5 Primary and backup protection 1.5.1 Primary protection 1.5.2 Backup protection 1.6 Directional protection 1.7 Relay models 1.8 Adaptive protection 2 Calculation of short circuit currents 2.1 Modelling for short circuit current calculations 2.1.1 Effect of the system impedance 2.1.2 Effect of rotating machinery 2.1.3 Types of fault duty 2.1.4 Calculation of fault duty values 2.2 Fault calculation for symmetrical faults 2.3 Symmetrical components 2.3.1 Importance and construction of sequence networks 2.3.2 Calculation of asymmetrical faults using symmetrical components 2.3.3 Equivalent impedances for a power system 2.4 Supplying the current and voltage signals to protection systems 2.5 General considerations of fault currents from DERs 2.6 Analysis tools for short circuit current calculation 3 Classification and function of relays 3.1 Classification 3.1.1 Construction 3.1.2 Incoming signal 3.1.3 Function 3.1.4 International identification of electrical devices 3.2 Electromechanical relays 3.2.1 Attraction relays 3.2.2 Relays with moveable coils 3.2.3 Induction relays 3.3 Evolution of protection relays 3.4 Numerical protection 3.4.1 General 3.4.2 Characteristics of numerical relays 3.4.3 Typical architectures of numerical relays 3.4.4 Standard functions of numerical relays 3.5 Supplies to the relay circuits 4 Current and voltage transformers 4.1 Voltage transformers 4.1.1 Equivalent circuit 4.1.2 Errors 4.1.3 Burden 4.1.4 Selection of VTs 4.1.5 Capacitor VTs 4.2 Current transformers 4.2.1 Equivalent circuit 4.2.2 Errors 4.2.3 AC saturation 4.2.4 Burden 4.2.5 Selection of CTs 4.2.6 Accuracy classes established by the ANSI standards 4.2.7 DC saturation 4.2.8 Precautions when working with CTs 5 Overcurrent protection 5.1 General 5.2 Types of overcurrent relay 5.2.1 Definite-current relays 5.2.2 Definite-time/current or definite-time relay 5.2.3 Inverse-time relays 5.3 Setting overcurrent relays 5.3.1 Setting instantaneous units 5.3.2 Coverage of instantaneous units protecting lines between substations 5.3.3 Setting the parameters of time-delay overcurrent relays 5.4 Constraints of relay coordination 5.4.1 Minimum short circuit levels 5.4.2 Thermal limits 5.4.3 Pickup values 5.5 Coordination across Dy transformers 5.5.1 Three-phase fault 5.5.2 Phase-to-phase fault 5.5.3 Phase-to-earth fault 5.6 Coordination with fuses 5.7 Coordination of negative-sequence units 5.8 Overcurrent relays with voltage control 5.9 Setting overcurrent relays using software techniques 5.10 Use of digital logic in numerical relaying 5.10.1 General 5.10.2 Principles of digital logic 5.10.3 Logic schemes 5.11 Adaptive protection with group settings change 5.12 Exercises 6 Fuses, reclosers and sectionalisers 6.1 Equipment 6.1.1 Reclosers 6.1.2 Sectionalisers 6.1.3 Fuses 6.2 Criteria for coordination of time/current devices in distribution systems 6.2.1 Fuse–fuse coordination 6.2.2 Recloser–fuse coordination 6.2.3 Recloser–recloser coordination 6.2.4 Recloser–relay coordination 6.2.5 Recloser–sectionaliser coordination 6.2.6 Recloser–sectionaliser–fuse coordination 6.2.7 Current-limiting fuses 6.3 Criteria for coordination of time/current devices under automated feeder reconfiguration 6.4 Criteria for coordination of time/current devices with DG intermittent sources 7 Directional overcurrent relays 7.1 Construction 7.2 Principle of operation 7.3 Relay connections 7.3.1 30° Connection (0° AMT) 7.3.2 60° Connection (0° AMT) 7.3.3 90° Connection (30° AMT) 7.3.4 90 Connection (45 AMT) 7.4 Directional earth-fault relays 7.5 Coordination of instantaneous units 7.6 Setting of time-delay directional overcurrent units 7.6.1 Pickup setting 7.6.2 Time dial setting 7.7 Importance of the directional protection 7.8 Exercises 8 Differential protection 8.1 General 8.2 Classification of differential protection 8.3 Transformer differential protection 8.3.1 Basic considerations 8.3.2 Selection and connection of CTs 8.3.3 Inrush restraint 8.3.4 Percentage of winding protected by the differential relay during an earth fault 8.3.5 Determination of the slope 8.3.6 Distribution of fault current in power transformers 8.3.7 Dual slope setting 8.3.8 Overexcitation (V/Hz) 8.3.9 High setting (this defeats the differential protection) 8.4 Differential protection for generators and rotating machines 8.5 Line differential protection 8.6 Busbar differential protection 8.6.1 Differential system with multiple restraint 8.6.2 High-impedance differential system 8.7 Exercises 9 Distance protection 9.1 General 9.2 Types of distance relays 9.2.1 Impedance relay 9.2.2 Directional relay 9.2.3 Reactance relay 9.2.4 Mho relay 9.2.5 Completely polarised mho relay 9.2.6 Relays with lens characteristics 9.2.7 Relays with polygonal characteristics 9.2.8 Relays with combined characteristics 9.3 Setting the reach and operating time of distance relays 9.4 The effect of infeeds on distance relays 9.5 The effect of arc resistance on distance protection 9.6 Residual compensation 9.7 Impedances seen by distance relays 9.7.1 Phase units 9.7.2 Earth-fault units 9.8 Power system oscillations 9.9 The effective cover of distance relays 9.10 Maximum load check 9.10.1 Mho relays 9.10.2 Relays with a polygonal characteristic 9.11 Drawing relay settings 9.11.1 Starting unit settings 9.11.2 Residual compensation constant setting 9.11.3 Time setting 9.11.4 Load check 9.11.5 Determination of the effective cover 9.12 Intertripping schemes 9.12.1 Underreach with direct tripping 9.12.2 Permissive underreach intertripping 9.12.3 Permissive overreach intertripping 9.13 Distance relays on series-compensated lines 9.14 Technical considerations of distance protection in tee circuits 9.14.1 Tee connection with infeeds at two terminals 9.14.2 Tee connection with infeeds at all three terminals 9.15 Use of distance relays for the detection of the loss of excitation in generators 9.16 Exercises 10 Protection of low-voltage systems 10.1 Protection devices 10.1.1 Overcurrent relays 10.1.2 Direct-acting devices in power breakers and MCCBs 10.1.3 Combined thermal relay contactor and fuse 10.1.4 MCCBs with numerical protection 10.2 Criteria for setting overcurrent protection devices associated with motors 10.2.1 Thermal relays 10.2.2 Low-voltage breakers 10.3 Arc flash 10.3.1 Arc flash calculation methods 10.3.2 Arc flash and approach boundary 10.3.3 Hazard study methodology 10.3.4 Electrode configurations 10.3.5 Selection of PPE 10.3.6 Arc thermal performance value 10.3.7 Energy break-open threshold 10.3.8 DC arc flash calculations 11 Industrial plant load shedding 11.1 Power system operation after loss of generation 11.2 Design of an automatic load shedding system 11.2.1 Simple machine model 11.2.2 Considerations of implementing a load shedding system 11.3 Criteria for setting frequency relays 11.3.1 Operating times 11.3.2 Determination of the frequency variation 11.4 Example of calculating and setting frequency relays in an industrial plant 11.4.1 Calculation of overload 11.4.2 Load to be shed 11.4.3 Frequency levels 11.4.4 Load shedding stages 11.4.5 Determination of the frequency relay settings 11.4.6 Verification of operation 11.5 Load shedding using logic schemes 12 Protection schemes and substation design diagrams 12.1 Protection schemes 12.1.1 Generator protection 12.1.2 Motor protection 12.1.3 Transformer protection 12.1.4 Line protection 12.2 Types of substations 12.3 Substation design diagrams 12.3.1 Single-line diagrams 12.3.2 Substation layout diagrams 12.3.3 Diagrams of AC connections 12.3.4 Diagrams of DC connections 12.3.5 Wiring diagrams 12.3.6 Digital substations 12.3.7 Logic diagrams 12.3.8 Cabling lists 13 Communication networks for power systems automation 13.1 IEC 61850 overview 13.2 Standard documents and features of IEC 61850 13.3 System Configuration Language 13.4 Challenges facing the testing of IEC 61850 devices 13.5 Configuration and verification of GOOSE messages 13.5.1 Configuration of the system 13.5.2 System verification test 13.6 Substation IT network 13.7 Process bus 14 Installation, testing and maintenance of protection systems 14.1 Installation of protection equipment 14.2 Testing protection schemes 14.2.1 Factory acceptance test 14.2.2 Commissioning tests 14.2.3 Maintenance test 14.2.4 Troubleshooting 14.3 Commissioning numerical protection 14.3.1 Setting the parameters 14.3.2 Performance tests 14.4 Protection relay testing considering IEC 61850 standard 14.4.1 Testing control and protection IEC 61850 GOOSE-based schemes 14.4.2 Testing protection IEC 61850 SV-based schemes 15 Protection of distributed generation systems 15.1 Types of distributed generation 15.1.1 Nonrenewable energy sources 15.1.2 Renewable energy sources 15.2 Protection of solar and wind facilities 15.2.1 Protective schemes for solar facilities 15.2.2 Protective schemes for wind facilities 15.3 Protection of distribution systems with DG penetration 16 Impact of stability conditions on protective relaying 16.1 Concepts and methods for analyses of power system stability 16.1.1 Rotor angle stability 16.1.2 Voltage stability 16.1.3 Frequency stability 16.2 Simplified model of the distribution system and transferred power 16.3 Power swings in a simple system 16.4 Solving the swing equation 16.5 Effect of a fault in the transient stability 16.6 Effect of the excitation system 16.7 Effect of load imbalance 16.8 Effect of high integration of renewables 16.9 Effect of high initial response excitation systems 16.10 Overview of system-dependent protection 16.10.1 Out-of-step (OOS) protection (78) 16.10.2 Loss of field (LOF) 16.10.3 Setting procedures for LOF and OOS protection 16.11 Exercises References Appendix: Solutions to exercises Index