Disturbance analysis for power systems Case Study 7.4 Troubleshooting a 345 kV Phase to Ground Fault Using Relay Targets Only 595 Case Study 7.5 Failure of a 345 kV Cable Connection Between a 300 MW Generator and a 345 kV Switchyard Causing a Phase to Ground Fault 603 Case Study 7.6 138 kV Cable Pot Head Failure Analysis Using Numerical Current Differential Relay Oscillography and Event Records 607 8 CASE STUDIES RELATED TO BREAKER FAILURE PROTECTION SYSTEM DISTURBANCES 615 8.1 Breaker Failure Protection Basics 616 Case Studies 626 Case Study 8.1 Tripping of a Combined Cycle 150 MW Plant by Undesired Operation of a Solid State Breaker Failure Relaying System 626 Case Study 8.2 115 kV Dual Breaker Failures Resulting in the Loss of a 1000 MW Plant and Associated Substations 634 Case Study 8.3 230 kV Substation Outage Due to Circuit Breaker Problems During the Clearing of a Close in Phase to Ground Fault 640 Case Study 8.4 Failure of a 230 kV Circuit Breaker Leading to Isolation of a 1000 MW Plant and Associated Substations 646 Case Study 8.5 Generator CB Failure During Automatic Synchronization of the Circuit Breaker 654 Case Study 8.6 Circuit Breaker Re strikes While Clearing Simultaneous Phase to Ground Faults on a 230 kV Double Circuit Tower 660 Case Study 8.7 345 kV Capacitor Bank Breaker Fault Coupled with an Additional Failure of a Dual SF6 Pressure 345 kV Breaker During the Clearing of the Fault 664 Case Study 8.8 Oil Circuit Breaker Failure Following the Clearing of a Failed 230 kV Surge Arrester 671 Case Study 8.9 Detection of a Remote Circuit Breaker Problem from Analysis of a Local Oscillogram Monitoring Line Currents and Voltages 676 Case Study 8.10 Blackout of a 138 kV Load Area Due to a Primary Relay System Failure and the Lack of DC Control Power for the Secondary Relay System Circuit 678 Case Study 8.11 Installation of Two 345 kV Breakers in Series Within a Ring Substation Configuration to Mitigate the Loss of Critical Lines During Breaker Failure Events 682 Case Study 8.12 Design of Two 138 kV Circuit Breakers in Series to Fulfill the Need of Breaker Failure Protection 682 9 PROBLEMS 685 Index 715 Case Study 4.7 Undesired Tripping of a Numerical Differential Relay During Manual Synchronization of a Hydro Unit 231 Case Study 4.8 Tripping of a 500 MW Combined Cycle Plant Triggered by a High Side 138 kV Phase to Ground Fault 236 Case Study 4.9 Tripping of a 110 MW Combustion Turbine Unit in a Combined Cycle Plant During a Power Swing 244 Case Study 4.10 Analysis of an 800 MW Generating Plant DFR Record for a Normally Cleared 345 kV Phase to Ground Fault 247 Case Study 4.11 Tripping of a 150 MW Combined Cycle Plant Due to a Failed Lead of One Generator Terminal Surge Capacitor 250 Case Study 4.12 Generator Stator Ground Fault in an 800 MW Fossil Unit 260 Case Study 4.13 Three Phase Fault at the Terminal of an 800 MW Generator Unit 265 Case Study 4.14 Three Phase Fault at the Terminal of a 50 MW Generator Due to a Cable Connection Failure 271 Case Study 4.15 Generator Stator Phase to Phase to Ground Fault Caused by Failure of the Rotor Fan Blade 276 Case Study 4.16 Undesired Tripping of a Pump Storage Plant During a Close in Phase to Ground 345 kV Line Fault 286 Case Study 4.17 Tripping of an 800 MW Plant and the Associated EHV Lines During a 345 kV Bus Fault 293 Case Study 4.18 Tripping of a 150 MW Combined Cycle Plant During an External 138 kV Three Phase Fault 296 Case Study 4.19 Tripping of a 150 MW Combined Cycle Plant During a Disturbance in the 138 kV Transmission System 303 Case Study 4.20 Undesired Tripping of a 150 MW Combined Cycle Plant Following Successful Clearing of a 138 kV Double Phase to Ground Fault 308 Case Study 4.21 Undesired Tripping of an Induction Generator by a Differential Relay Having a Capacitor Bank Within the Protection Zone 311 Case Study 4.22 Undesired Tripping of a Steam Unit Upon Its First Synchronization to the System During the Commissioning Phase of a Combined Cycle Plant 314 Case Study 4.23 Sequential Shutdown of a Steam Driven Generating Unit as Part of a 500 MWCombined Cycle Plant 318 3.34 Shunt Capacitor Bank Outrush into Close in System Faults 149 3.35 SCADA Closing into a Three Phase Fault 153 3.36 Automatic Reclosing into a Permanent Line to Ground Fault 154 3.37 Successful High Speed Reclosing Following a Line to Ground Fault 155 3.38 Zero Sequence Mutual Coupling–Induced Voltage 156 3.39 Mutual Coupling Phenomenon Causing False Tripping of a High Impedance Bus Differential Relay During a Line Phase to Ground Fault 159 3.40 Appearance of Nonsinusoidal Neutral Current During the Clearing of Three Phase Faults 162 3.41 Current Reversal on Parallel Lines During Faults 164 3.42 Ferranti Voltage Rise 166 3.43 Voltage Oscillation on EHV Lines Having Shunt Reactors at their Ends 168 3.44 Lightning Strike on an Adjacent Line Followed by a C g Fault Caused by a Separate Lightning Strike on the Monitored Line 172 3.45 Spill Over of a 345 kV Surge Arrester Used to Protect a Cable Connection Prior to its Failure 173 3.46 Scale Saturation of an A D Converter Caused by a Calibration Setting Error 174 3.47 Appearance of Subsidence Current at the Instant of Fault Interruption 176 3.48 Energizing of a Medium Voltage Motor that has an Incorrect Formation of the Stator Winding Neutral 177 3.49 Phase Angle Change from Loading Condition to Fault Condition 179 4 CASE STUDIES RELATED TO GENERATOR SYSTEM DISTURBANCES 183 4.1 Generator Protection Basics 184 Case Studies 186 Case Study 4.1 Appearance of Double Frequency (120 Hz) Current in a Hydrogenerator Rotor Due to Stator Negative Sequence Current Flow During a 115 kV Phase to Ground Fault 186 Case Study 4.2 Inadvertent (Accidental) Energization of a 170 MW Hydro Unit 193 Case Study 4.3 Loss of Excitation for a 200 MW Generating Unit Caused by Human Error 204 Case Study 4.4 Loss of Excitation Trip in an 1100 MW Unit 212 Case Study 4.5 Mis synchronization of a 50 MW Steam Unit for a Combined Cycle Plant 214 Case Study 4.6 Mis synchronization of a 200 MW Hydro Unit 222 Case Study 5.12 Phase to Phase Fault Evolving into a Three Phase Fault at the High Side of a 5 MVA 13.8 4.16 kV Station Service Transformer 414 Case Study 5.13 Phase to Phase Fault Evolving into a Three Phase Fault at the 13.8 kV Bus Connection of a 2 MVA 13.8 0.480 kV Station Service Enclosure 420 Case Study 5.14 Phase to Phase Fault in a 13.8 kV Switchgear Caused by Heavy Rain Evolving into a Three Phase Fault 426 Case Study 5.15 Undesired Operation of a Numerical Transformer Differential Relay Due to a Missing CT Cable Connection as an Input to the Relay Wiring 430 Case Study 5.16 Phase to Ground Fault Caused by Flashover of a Transformer 115 kV Bushing Due to a Bird Droppings 434 Case Study 5.17 Using a Transformer Numerical Relay Oscillography Record to Analyze Phase to Ground Faults in a 4.16 kV Low Resistance Grounding Supply 439 Case Study 5.18 Phase to Phase Fault Caused by a Squirrel in a 13.8 kVCable Bus Which Evolves into a Three Phase Fault 447 Case Study 5.19 13.8 kV Transformer Lead Phase to Phase Fault Due to Animal Contact Evolving into a 115 kV Transformer Bushing Fault 451 Case Study 5.20 Undesired Tripping of a Numerical Multifunction Transformer Relay by Assertion of a Digital Input Wired to the Buchholz Relay Trip Output 456 6 CASE STUDIES RELATED TO OVERHEAD TRANSMISSION LINE SYSTEM DISTURBANCES 461 6.1 Line Protection Basics 463 6.2 Case Studies 466 Case Study 6.1 Using a DFR Record From One End Only to Determine Local and Remote End Clearing Times for a Line to Ground Fault 466 Case Study 6.2 Analysis of Clearing Times for a Phase to Ground Fault from Both Ends of a 345 kV Transmission Line Using Oscillograms from One End Only 469 Case Study 6.3 Analysis of a Three Phase Fault Caused by Lightning 471 Case Study 6.4 Analysis of a Double Phase to Ground 765 kV Fault Caused by Lightning 473 Case Study 6.5 Assessment of Transmission Tower Footing Resistance by Analyzing a Three Phase to Ground Fault Caused by Lightning 476 Case Study 4.24 Wiring Errors Leading to Undesired Generator Numerical Differential Relay Operation During the Commissioning Phase of a New Unit 320 Case Study 4.25 Phasing a New Generator into the System Prior to Commissioning 324 Case Study 4.26 Third Harmonic Undervoltage Element Setting Procedure for 100% Stator Ground Fault Protection 327 Case Study 4.27 Basis for Setting the Generator Relaying Elements to Provide System Backup Protection 330 5 CASE STUDIES RELATED TO TRANSFORMER SYSTEM DISTURBANCES 335 5.1 Transformer Basics 336 5.2 Transformer Differential Protection Basics 344 5.3 Case Studies 347 Case Study 5.1 Energization of a 5 MVA 13.8 4.16 kV Station Service Transformer with a 13.8 kV Phase to Phase Bus Fault Within the Transformer Differential Protection Zone 347 Case Study 5.2 Lack of Protection Redundancy for a Generator Step up Transformer Leads to Interruption of a 230 kV Area 353 Case Study 5.3 Undesired Operation of a Numerical Transformer Differential Relay Due to a Relay Setting Error in the Winding Configuration 357 Case Study 5.4 Location of a 13.8 kV Switchgear Phase to Phase Fault Using Transformer Differential Numerical Relay Fault Records 363 Case Study 5.5 Operation of a Unit Step Up Transformer with an Open Phase on the 13.8 kV Delta Winding 370 Case Study 5.6 Using a Transformer Phasing Diagram Digital Fault Recorder Record and Relay Targets to Confirm the Damaged Phase of a Unit Auxiliary Transformer Failure 375 Case Study 5.7 Failure of a 450 MVA 345 138 13.2 kV Autotransformer 381 Case Study 5.8 Failure of a 750 kVA 13.8 0.480 kV Station Service Transformer Due to a Possible Ferroresonance Condition 387 Case Study 5.9 Undesired Tripping of a Numerical Transformer Differential Relay During an External Line to Ground Fault 394 Case Study 5.10 Undesired Operation of Numerical Transformer Differential Relays During Energization of Two 75 MVA 138 13.8 kV GSU Transformers 407 Case Study 5.11 Undesired Operation of a Numerical Transformer Differential Relay During Energization of a 5 MVA 13.8 4.16 kV Station Service Transformer 411 Preface xvii 1 POWER SYSTEM DISTURBANCE ANALYSIS FUNCTION 1 1.1 Analysis Function of Power System Disturbances 2 1.2 Objective of DFR Disturbance Analysis 4 1.3 Determination of Power System Equipment Health Through System Disturbance Analysis 5 1.4 Description of DFR Equipment 6 1.5 Information Required for the Analysis of System Disturbances 7 1.6 Signals to be Monitored by a Fault Recorder 8 1.7 DFR Trigger Settings of Monitored Voltages and Currents 10 1.8 DFR and Numerical Relay Sampling Rate and Frequency Response 11 1.9 Oscillography Fault Records Generated by Numerical Relaying 11 1.10 Integration and Coordination of Data Collected from Intelligent Electronic Devices 12 1.11 DFR Software Analysis Packages 12 1.12 Verification of DFR Accuracy in Monitoring Substation Ground Currents 21 1.13 Using DFR Records to Validate Power System Short Circuit Study Models 24 1.14 COMTRADE Standard 31 2 PHENOMENA RELATED TO SYSTEM FAULTS AND THE PROCESS OF CLEARING FAULTS FROM A POWER SYSTEM 33 2.1 Shunt Fault Types Occurring in a Power System 33 2.2 Classification of Shunt Faults 34 2.3 Types of Series Unbalance in a Power System 39 2.4 Causes of Disturbance in a Power System 39 2.5 Fault Incident Point 40 2.6 Symmetric and Asymmetric Fault Currents 41 2.7 Arc Over or Flashover at the Voltage Peak 44 2.8 Evolving Faults 48 2.9 Simultaneous Faults 51 2.10 Solid or Bolted (RF1 40) Close in Phase to Ground Faults 52 2.11 Sequential Clearing Leading to a Stub Fault that Shows a Solid (RF1 40) Remote Line to Ground Fault 53 2.12 Sequential Clearing Leading to a Stub Fault that Shows a Resistive Remote Line to Ground Fault 54 2.13 High Resistance Tree Line to Ground Faults 56 2.14 High Resistance Line to Ground Fault Confirming the Resistive Nature of the Fault Impedance When Fed from One Side Only (Stub) 58 2.15 Phase to Ground Faults on an Ungrounded System 59 2.16 Current in Unfaulted Phases During Line to Ground Faults 60 3.8 Appearance of Third Harmonic Voltage at Generator Neutral 104 3.9 Variations of Generator Neutral Third Harmonic Voltage Magnitude During System Faults 106 3.10 Generator Active and Reactive Power Outputs During a GSU High Side L g Fault 107 3.11 Loss of Excitation of a 200 MW Unit 108 3.12 Generator Trapped (Decayed) Energy 110 3.13 Nonzero Current Crossing During Faults and Mis Synchronization Events 112 3.14 Generator Neutral Zero Sequence Voltage Coupling Through Step Up Transformer Interwinding Capacitance During a High Side Ground Fault 113 3.15 Energizing a Transformer with a Fault on the High Side within the Differential Zone 115 3.16 Transformer Inrush Currents 118 3.17 Inrush Currents During Energization of the Grounded Wye Side of a YG Delta Transformer 120 3.18 Inrush Currents During Energization of a Transformer Delta Side 121 3.19 Two Phase Energization of an Autotransformer with a Delta Winding Tertiary During a Simultaneous L g Fault and an Open Phase 124 3.20 Phase Shift of 30Across the Delta Wye Transformer Banks 127 3.21 Zero Sequence Current Contribution from a Remote Two Winding Delta YG Transformer 128 3.22 Conventional Power Regulating Transformer Core Type Acting as a Zero Sequence Source 129 3.23 Circuit Breaker Re Strikes 130 3.24 Circuit Breaker Pole Disagreement During a Closing Operation 132 3.25 Circuit Breaker Opening Resistors 133 3.26 Secondary Current Backfeeding to Breaker Failure Fault Detectors 134 3.27 Magnetic Flux Cancellation 136 3.28 Current Transformer Saturation 138 3.29 Current Transformer Saturation During an Out of Step System Condition Initiated by Mis Synchronization of a Generator Breaker 141 3.30 Capacitive Voltage Transformer Transient 143 3.31 Bushing Potential Device Transient During Deenergization of an EHV Line 144 3.32 Capacitor Bank Breaker Re Strike Following Interruption of a Capacitor Normal Current 146 3.33 Capacitor Bank Closing Transient 147 2.17 Line to Ground Fault on the Grounded Wye (GY) Side of a Delta GY Transformer 63 2.18 Line to Line Fault on the Grounded Wye Side of a Delta GY Transformer 65 2.19 Line to Line Fault on the Delta Side of a Delta GY Transformer with No Source Connected to the Delta Winding 66 2.20 Subcycle Relay Operating Time During an EHV Double Phase to Ground Fault 68 2.21 Self Clearing of a C g Fault Inside an Oil Circuit Breaker Tank 69 2.22 Self Clearing of a B g Fault Caused by a Line Insulator Flashover 70 2.23 Delayed Clearing of a Pilot Scheme Due to a Delayed Communication Signal 71 2.24 Sequential Clearing of a Line to Ground Fault 72 2.25 Step Distance Clearing of an L g Fault 74 2.26 Ground Fault Clearing in Steps by an Instantaneous Ground Element at One End and a Ground Time Overcurrent Element at the Other End 76 2.27 Ground Fault Clearing by Remote Backup Following the Failures of Both Primary and Local Backup (Breaker Failure) Protection Systems 78 2.28 Breaker Failure Clearing of a Line to Ground Fault 79 2.29 Determination of the Fault Incident Point and Classification of Faults Using a Comparison Method 81 3 POWER SYSTEM PHENOMENA AND THEIR IMPACT ON RELAY SYSTEM PERFORMANCE 85 3.1 Power System Oscillations Leading to Simultaneous Tripping of Both Ends of a Transmission Line and the Tripping of One End Only on an Adjacent Line 86 3.2 Generator Oscillations Triggered by a Combination of L g Fault Loss of Generation and Undesired Tripping of Three 138 kV Lines 91 3.3 Stable Power Swing Generated During Successful Synchronization of a 200 MW Unit 95 3.4 Major System Disturbance Leading to Different Oscillations for Different Transmission Lines Emanating from the Same Substation 96 3.5 Appearance of 120 Hz Current at a Generator Rotor During a High Side Phase to Ground Fault 98 3.6 Generator Negative Sequence Current Flow During Unbalanced Faults 101 3.7 Inadvertent (Accidental) Energization of a 170 MW Hydro Generating Unit 102 Case Study 6.6 115 kV Phase to Ground Fault Cleared First from a Solidly Grounded System Then Connected and Cleared from an Ungrounded System 478 Case Study 6.7 345 kV Phase to Ground Fault (C g) Caused by an Act of Vandalism 485 Case Study 6.8 345 kV Phase to Ground (A g) Fault Due to an Accident Along the Line Right of Way 489 Case Study 6.9 False Tripping of a 138 kV Current Differential Relaying System During an External Phase to Ground Fault 495 Case Study 6.10 Undesired Operation of a 13.8 kV Feeder Ground Relay During a Three Phase Fault Due to an Extra CT Circuit Ground 502 Case Study 6.11 Correction of a System Model Error from Analysis of a Failure of a Post Insulator Associated with a 115 kV Disconnect Switch 512 Case Study 6.12 Location of a 345 kV Line Fault Protected by Electromechanical Distance Relays Using Information from a DFR Record 519 Case Study 6.13 Location of an Outdoor 13.8 kV Switchgear Fault at a Cogeneration Facility Using a DFR Fault Record from a Remote Substation 524 Case Study 6.14 Breakage (Failure) of a 345 kV Subconductor Bundle During a High Resistance Tree Fault Due to the Heavily Loaded Line Sagging to a Tree 529 Case Study 6.15 115 kV Phase to Phase Fault Caused by Failure of a Circuit Switcher 536 Case Study 6.16 Undesired Tripping of a 115 kV Feeder Due to a Setting Application Error in the Time Overcurrent Element for a Numerical Line Protection Relay 539 Case Study 6.17 Mitigation of Mutual Coupling Effects on the Reach of Ground Distance Relays Protecting Highand Extrahigh Voltage Transmission Lines 544 7 CASE STUDIES RELATED TO CABLE TRANSMISSION FEEDER SYSTEM DISTURBANCES 571 Case Studies 572 Case Study 7.1 Optimum Design of Relaying Protection Zones Leads to Quick Identification of a Faulted 345 kV Submarine Cable Section 572 Case Study 7.2 Undesired Operation of a 138 kV Cable Feeder Differential Relay During the Commissioning Phase of a 500 MW Plant 578 Case Study 7.3 Phase to Ground Fault Caused by Failure of a 345 kV Cable Connection Between the Generator and the Switchyard Accompanied by Mechanical Failure of One of the Cable Pot Head Phases 588