Voltage Control and Protection in Electrical Power Systems (eBook)

Dr. Sandro Corsi, is a senior scientist and project manager at CESI S.p.A.. Formerly, he has been manager and head of the voltage control office at ENEL Research Department. His main interests are in studies, consultancies, specifications, design and applications in real power systems of grid voltage controls, generator controls, power electronics, HVDC systems, substation automation, grid security and protection systems, advanced control and communication methods and technologies. He has a wide experience in field applications, in Italy and further afield, of grid support control systems. His international experience also includes projects related to SCADA/EMS, tailored energy markets and grids integration to UCTE/ETNSO pool. He pioneered the studies and applications of the “Transmission Network Automatic Voltage Regulation and Wide Area Protection Systems”. On renewable energy, he has a long experience of studies and field applications of special control systems in photovoltaic, wind and fuel cells generators and power stations. Member of: CIGRE, IEEE-PES and CEI WGs and SCs. Member of IREP Board of Directors and IET-GTD; IJRET Editorial Boards. Author of more than 100 technical papers in the main Conferences Proceedings and Reviews on power system stability, control and protection. Reviewer of IEEE-Transactions, and for IET, Elsevier, EPSR , IJRET and International Conference papers.

Series Editors’ Foreword 7
Preface 9
Acknowledgements 12
Contents 14
Abbreviations and Acronyms 20
Introduction 22
References 26
Part I 28
Voltage Control Resources 28
Chapter-1 29
Relationship Between Voltage and Active and Reactive Powers 29
1.1 Grid Short Lines 29
1.1.1 Reactive Power Transfer 31
1.1.2 Losses 32
1.2 Reactive Loads 33
1.3 Grid Medium-Long Length Lines 34
1.4 Grid as a Combination of Loads and Lines 36
References 37
Chapter-2 38
Equipment for Voltage and Reactive Power Control 38
2.1 Introduction 38
2.2 Reactive Power Compensation Devices 39
2.2.1 Shunt Capacitors 39
2.2.2 Mechanically Switched Capacitors (MSC) 40
2.2.3 Shunt Reactors 41
2.2.4 Mechanically Switched Reactors (MSR) 42
2.2.5 Multiple Compensation Device Operating Point 43
2.3 Voltage and Reactive Power Continuous Control Devices 45
2.3.1 Synchronous Generators 45
ECS with Exciting Dynamo 46
ECS with Alternator and Rotating Diodes 47
ECS with Static Exciter 48
ECS Model Parameters 49
Synchronous Generator as Reactive Power Source 49
2.3.2 Synchronous Compensators 55
2.3.3 SVG: Static VAR Generators 57
Thyristor-Controlled Reactor (TCR) 58
Thyristor-Switched Capacitor (TSC) 59
Fixed Capacitor and Thyristor Controlled Reactor (FC-TCR) 61
Thyristor-Switched Capacitor, Thyristor-Controlled Reactor (TSC-TCR) 63
2.3.4 Static VAR Compensators (SVCs) 66
SVC Voltage Control Requirements 67
SVC Regulation Slope 68
2.3.5 Static Compensators (STATCOMs) 69
STATCOM Voltage Control Requirements 72
STATCOM Regulation Slope 74
2.3.6 Unified Power Flow Control (UPFC) 74
Fundamentals of the Shunt Voltage Source Converter 76
Fundamentals of the Series Voltage Source Converter 77
Fundamentals of the UPFC 80
UPFC Voltage Control Requirements 85
2.4 Voltage and Reactive Power Discrete Control Devices: On-load Tap-changing Transformers 87
2.4.1 Generalities 87
2.4.2 Output Voltage Dependence on Current Turns Ratio 88
2.4.3 Static Characteristic of the Transformer 90
2.4.4 Link of Voltage, Reactive Power and Turns Ratio in OLTC Transformer Applications 95
Combined Use of OLTC and Reactive Power Injections in Transmission Networks 95
Radial Transmission/Distribution System with Two Cascaded OLTC Transformers 99
2.4.5 Regulating Transformers 101
In-Phase Regulating Transformer (IPRT) 101
Phase-Shifting Transformers (PSTs) 101
2.5 Conclusion 103
References 104
Chapter-3 106
Grid Voltage and Reactive Power Control 106
3.1 General Considerations 106
3.2 Voltage-Reactive Power Manual Control 110
3.2.1 Manual Voltage Control by Reactive Power Flow 111
3.2.2 Manual Voltage Control by Network Topology Modification 111
3.3 Voltage-Reactive Power Automatic Control 111
3.3.1 Automatic Voltage Control by OLTC Transformer 112
3.3.2 Automatic Voltage Control (AVR) of Generator Stator Edges 115
Linear Analysis of Generator Voltage Control Loop 117
3.3.3 Automatic Voltage Control by Generator Line Drop Compensation (Compounding) 124
Objective of Compounding 124
Link Between Voltage and Reactive Power 125
Line Drop Compensation (Compounding) 126
Line Drop Compensation and Stability 128
Line Drop Compensation Simplified Feedback 130
3.3.4 Generalities on Automatic High Side Voltage Control at a Substation 131
Voltage Control at a Substation 132
3.3.5 Automatic High Side Voltage Control at a Power Plant 133
Principal Scheme 133
Model of the Power Plant 133
High Side Voltage Regulator 137
3.3.6 Automatic Voltage-Reactive Power Control by SVC 143
SVC Voltage Regulation 143
SVC Voltage Control Drop 146
Dynamic Behaviour of SVC 149
Dynamic Behaviour of SVC Reactive Power Control 153
3.3.7 Automatic Voltage-Reactive Power Control by STATCOM 158
STATCOM Grid Voltage Regulation 159
STATCOM Voltage Control Drop 161
Dynamic Behaviour of the STATCOM 165
Dynamic Behaviour of the STATCOM Reactive Power Control 168
3.3.8 Automatic Voltage-Reactive Power Control by UPFC 173
UPFC Control Schemes 173
UPFC Shunt Converter Control 174
UPFC Series Converter Control 174
UPFC Dynamic Behaviour 176
3.4 Conclusion 181
References 182
Part II 184
Wide Area Voltage Control 184
Introduction to Part II 184
Chapter-4 185
Grid Hierarchical Voltage Regulation 185
4.1 Structure of the Hierarchy 185
4.1.1 Generalities 185
4.1.2 Basic SVR and TVR Concepts 189
4.1.3 Primary Voltage Regulation 190
4.1.4 Secondary Voltage Regulation: Architecture and Modelling 194
Principle of Secondary Voltage Regulation 194
Dynamic Model of Secondary Voltage Control System 197
SVR Control Structure 200
Reference Transients 206
4.1.5 Tertiary Voltage Regulation 210
4.2 SVR Control Areas 214
4.2.1 Procedure to Select Pilot Nodes and Define Control Areas 214
Analytical Procedure for Selecting Pilot Nodes 214
4.2.2 Procedure to Select Control Generators 217
Analytical Procedure for Selecting Control Generators 218
4.2.3 Power Flow and Optimal Power Flow Computation in the Presence of Secondary Voltage Regulation 219
4.2.4 Examples of Pilot Node and Control Power Station Selection 220
Pilot Nodes and Control Power Stations in Italy 221
Pilot Nodes and Control Power Stations in the Taiwan Grid 223
Pilot Nodes and Control Power Stations in South Korea 226
Pilot Nodes and Control Power Stations in South Africa 226
4.2.5 Examples of Control Apparatuses Required by SVR 234
The SQR Apparatus: Functional Design and Technological Issues 234
RVR Apparatus: Functional Design and Technological Issues 237
NVR Apparatus: Functional Design and Technological Issues 243
4.2.6 SVR Dynamic Performance During Tests in Real Grids 245
4.2.6.1 Verified Performance and Field Tests 245
4.2.7 General Considerations on Practical Issues 252
4.3 Conclusion 253
References 254
Chapter-5 257
Examples of Hierarchical Voltage Control Systems Throughout the World 257
5.1 French Hierarchical Voltage Control System 257
5.1.1 General Overview 257
5.1.2 Original Secondary Voltage Regulation and Its Limits 258
5.1.3 Coordinated Secondary Voltage Control (CSVC) 261
5.1.4 Performance and Results of Simulations 264
Voltage Control in Case of Failure and Load Variation 264
5.1.5 Final Comments on French Hierarchical Voltage Control Power System 264
5.2 Italian Hierarchical Voltage Control System 266
5.2.1 General Overview 266
5.2.2 Power System Operation Improvement 268
Voltage Control System Dynamics 268
Voltage Stability Limit Increase 269
Network Loss Reduction 270
5.2.3 Final Remarks on Italian Hierarchical Voltage Control System 272
5.3 Brazilian Hierarchical Voltage Control System 272
5.3.1 General Overview 272
5.3.2 Results of Study Simulations 274
SVR Step Response 274
Load Variation 275
Single Contingency Case 276
Loading the Light Subsystem 276
5.3.3 Conclusions on the Brazilian Voltage Control System 278
5.4 Romanian Hierarchical Voltage Control System 279
5.4.1 Characteristics of the Studied System 279
5.4.2 SVR Area Selection 279
Line Outage 281
Generator Outage 283
5.5 Chinese Hierarchical Voltage Control System 284
References 285
Chapter-6 287
SVR Dynamic Tests with Contingencies 287
6.1 Tests Without Contingencies in Large Power Systems 287
6.1.1 Tests on Italian Hierarchical Voltage Control System 288
6.1.2 Tests on South Korean Hierarchical Voltage Control System 291
6.1.3 Tests on South African Hierarchical Voltage Control System 291
Test on SVR with Load Variation in One Area Only 294
Test Like § 6.1.3.1, But with PVR Alone. Load Steps at Pegasus Area 299
Test on SVR with Step Variation at All the Pilot Nodes Voltage Set-Points 302
6.2 Tests with Contingencies in Large Power Systems 306
6.2.1 Tests on Line-Opening 306
Performance Comparison Between SVR with PVR in South Korean Hierarchical Voltage Control System 306
Performance Comparison Between SVR with PVR in Taiwan Hierarchical Voltage Control System 308
Performance Comparison Between SVR with PVR in South African Hierarchical Voltage Control System 310
6.2.2 Tests on Generator Tripping 314
Performance Comparison Between SVR with PVR in South African Hierarchical Voltage Control System 314
Performance Comparison Between SVR with PVR in Taiwan Hierarchical Voltage Control System 318
References 320
Chapter-7 321
Economics of Voltage Ancillary Service 321
7.1 General Overview 321
7.2 Cost/Benefit Analysis of Voltage Service 323
7.2.1 Generation Costs 323
Capital Costs 324
Operation Costs 324
7.2.2 Transmission Costs 325
Capital Costs 325
Operation Costs 325
7.2.3 Voltage-VAR Control Benefits 326
Example of Economic Benefits on South African Transmission Grid 327
Reduction of Switching Manoeuvres by SVR-TVR in South African Grid 328
Loss Reduction Example Due to SVR benefits in South Korean Grid 329
Example of economic benefit evaluation for a large power system (50-GW peak load) 331
7.2.4 SVR-TVR Cost/Benefit Illustrative Case 331
7.3 Economic Performance Recognition of Voltage Service 332
7.3.1 Voltage Service with SVR: Role Played by Power Plant Voltage and Reactive Power Regulator (SQR) 334
7.3.2 Voltage Service Indicators 335
Index of Generator Available Capability 336
Index of Generator Available Voltage Field 337
New Power Plant Meter For Voltage Service 338
7.3.3 Simplicity, Correctness and Indubitableness of Proposed Indicators 339
Final Remarks On New Voltage Service Meter 340
References 340
Chapter-8 342
Voltage Stability 342
8.1 General Overview on Stability 342
8.2 Electrical Power System Stability 344
8.2.1 Transient Stability 345
8.2.2 Steady-State Stability 349
8.2.3 Generator AVR Contribution to Steady-State Stability 351
Electromechanical Oscillation Damping Through Additional Feedbacks on Generator Voltage Control Loop 353
8.2.4 SVR Contribution to Angle Stability 357
8.3 Voltage Stability: Introduction 364
8.3.1 Relationship Between Load Power and Network Voltage 366
V-P Curve Basics 369
Proposed Equivalent System 373
Analysis of V-P Curves of the Test System 376
V-P Curve Analysis for a More Realistic Generic Load Representation 388
V-P Curve Analysis for The Italian System 389
Understanding and Modeling Voltage Instability 398
V-P Curve in Presence of Grid Automatic Voltage Regulation 400
8.3.2 Distinguishing Voltage Instability from Voltage Collapse 405
Further Examples of Voltage Instability and Collapse 408
8.3.3 Voltage Instability and Bifurcation Analysis 412
Equilibrium and Stability of Dynamic Systems 412
Equilibrium Points and Trajectories with Saddle-Node Bifurcation 417
References 422
Chapter-9 424
Voltage Instability Indicators 424
9.1 Introduction 425
9.2 Off-line Voltage Instability Indicators 427
9.2.1 Basics of Off-line Indices Based on Jacobian Singular Values 429
9.2.2 Basics of Off-line Indices Based on Load Margin 432
9.2.3 Final Comment 433
9.3 Real-time PMU-based Voltage Instability Indicators 434
9.3.1 Introduction 434
9.3.2 Thevenin Equivalent Identification Algorithm 436
9.3.3 Description of Proposed Real-time Identification Algorithm 441
9.3.4 Sensitivity Analysis of the Identification Method 444
9.3.5 Algorithm Application to Dynamic Thevenin Equivalent 449
9.3.6 Algorithm Application to the Italian 380/20-kV Network 453
9.4 Real-time Voltage Instability Indicators V-WAR–based 462
9.4.1 The Real-time and On-line Index 463
9.4.2 Voltage Stability Index Definition 464
9.4.3 Voltage Stability Index Computation and Meaning 464
9.4.4 Crucial Role Played by Tertiary Voltage Regulation 465
9.4.5 Voltage Stability Index Control Function 466
9.4.6 Functional Performances 466
9.4.7 Comparison with Off-line Voltage Stability Indices 471
9.5 Real-time Voltage Instability Indicators Based on Grid Area Reactive Power Injection 473
9.6 A Variety of Real-time Voltage Instability Indicators Based on Phasor Measurements Units Data 474
9.6.1 Real-time Indices Based on the Thevenin Equivalent Identification Method 475
9.6.2 Index Performance in Front of Load Increase 478
9.6.3 Index Performance in Front of Large Perturbations 482
9.7 Final Remarks 485
References 486
Chapter-10 488
Voltage Control on Distribution Smart Grids 488
10.1 Introduction 488
10.1.1 Generalities 489
Generality of PC Voltage Regulation 489
Generality of PC Frequency Regulation 489
Generality of PC Power Flow Regulation at the HV Bus Bar 490
Generality of PC Back-Up Feeding by Neighbouring MV Network 490
10.1.2 Chapter Objective 490
10.2 Generalities on Medium Voltage Grid and Primary Cabin Schemes 491
10.3 Generalities of Primary Cabin Voltage Control 493
10.4 PCVR Basic Control Schemes 496
10.4.1 OLTC Operation in Presence of PCVR 496
10.4.2 Islanded Grid Voltage Regulation 498
10.4.3 Automatic Voltage Regulation of HV or MV PC Bus Bars 498
10.4.4 Block Diagrams of PCVR Control Functions 500
10.5 Automatic Reactive Power Flow Regulation on the PC HV Bus Bar 502
10.6 Analysis of PCVR and PCQR Control Logicsand Results 504
10.6.1 Case of Reactive Power Flow Entering Feederby HV Bus Bar 507
10.6.2 Case of Reactive Power Flow Sent by Feeder into PC HV Bus Bar 510
10.6.3 OLTC Tap Control by PC-CC Operating as PCVR 512
Low Voltage in the Feeder with VMV < ?Vref
High Voltage in the Feeder with VMV < ?Vref
10.6.4 OLTC Control by PC-CC During PCQR Operation 514
10.7 Conclusions 516
References 517
Chapter-11 519
Wide Area Voltage Protection 519
11.1 Introduction 520
11.2 Area Voltage Protection Based on SVR-TVR and Real-Time Indicators 523
11.2.1 Basics of Real-time SVR-TVR VSIj(t) Index Computing 524
11.2.2 Basics of Real-time V-WAR and V-WAP Coordination 525
Use of VSIj(t) Indicator by V-WAR 525
11.2.3 Wide Area Voltage Stability Protection Philosophy Based on SVR-TVR VSIj(t) 527
Use of VSIj(t) Indicator by the V-WAP 527
11.2.4 Simulation Results of V-WAP Based on SVR-TVR VSIj(t) 530
11.3 Area Voltage Protection Based on Reactive Power Inflow Real-time Voltage Stability Indicator 534
11.3.1 Basics of Real-time VSIi(t) Index Linked to V-WAP Referring to a Power System Area-i: 539
11.3.2 Wide Area Voltage Stability Protection Philosophy Based on dQin_tot(t) Indicator 540
Load Shedding 540
11.3.3 Simulation Results of V-WAP Based on dQin_tot(t) 542
11.4 Area Voltage Protection Based on PMU and Related Real-time Voltage Stability Indicator 550
11.4.1 Basics of Real-time VSI-PMU(t) Index Linked to V-WAP 551
Synthetic Description of Proposed Algorithm 551
11.4.2 Wide Area Voltage Stability Protection Philosophy Based on VSI-PMU(t) 553
Voltage Instability Risk Prediction 553
Prediction Modulation by Tuning Control Parameter of Identification Algorithm 554
11.4.3 V-WAP Based on VSI-PMU(t) Simulation Results 555
Wide Area VSI Warning 555
11.5 Area Voltage Protection Based on System Jacobian Computing Combined with OEL and OLTC Real-time Information 559
11.6 Conclusions 561
References 563
Appendix 565
Appendix A 565
Synchronous Machine Ideal Model 565
Generator Operating on a Large Power System 568
Reference 576
Index 577