Accessible reference dealing with (partial discharge) PD measurement in all types of high voltage equipment using modern digital PD detectors

Practical Partial Discharge Measurement on Electrical Equipmentis a timely update in the field of partial discharges (PD), covering both holistic concepts and specific modern applications in one volume. The first half of the book educates the reader on what PD is and the general principles of how it is measured and interpreted. The second half of the book is similar to a handbook, with a chapter devoted to PD measurements in each type of high voltage (HV) equipment. These chapters contain specific information of the insulation system design, causes of PD in that equipment, off-line and on-line measurement methods, interpretation methods, and relevant standards.

The work is authored by four well-known experts in the field of PD measurement who have published hundreds of technical papers on the subject and performed thousands of PD measurements on all the different types of HV equipment covered in the book. The authors have also had relationships with PD detector manufacturers, giving them key insights into test instruments and practical measurements.

Sample topics covered in the work include:Physics of PD, discharge phenomena (contact sparking and vibration sparking), and an introduction to PD measurement (electrical, optical, acoustic, and chemical)Electrical PD detection (types of sensors), RF PD detection (antenna, TEV), and PD instrumentation and displayOff-line and on-line PD measurements, general principles of PD interpretation, and laboratory PD testing of lumped test objectsPD in different types of HV equipment (power cables, power transformers, air insulated metal-clad switchgear, rotating machines, gas-insulated switchgear, and more)

For HV equipment OEMs, users of HV equipment, or employees of companies that provide PD testing services to clients,Practical Partial Discharge Measurement on Electrical Equipmentis an essential reference to help understand general concepts about the topic and receive expert guidance during specific practical applications.

Greg C. Stone has a PhD in electrical engineering with over 45-years experience in performing PD testing on rotating machines and other equipment for a large electric power utility; as well as with PD equipment manufacturer Iris Power L.P., which he co-founded. He has many technical awards for his work from the IEEE, CIGRE, IEC and EPRI, and is an IEEE Fellow.

Andrea Cavallini, PhD, is with the University of Bologna, Italy where he has researched PD theory and PD test methods for 24 years, particularly for power cables, stator windings and other HV equipment. He was also a co-founder of TechImp S.r.L, a manufacturer of PD test equipment. He has over 200 papers in the PD field, including the development of the TF map method for noise and PD source identification. He is an IEEE Fellow.

Glenn Behrmann worked for over 20 years on PD measurements for GIS and rotating machines at ABB in Switzerland and its successor companies. He has been active in creating CIGRE Technical Brochures in this area, written many papers in the field, as well as helping to lead the efforts to draft IEC 62478, and revise IEC 60270 and IEEE 454. He has a BSEE from Union College in the USA.

Claudio Angelo Serafino is head of the Test and Measurement Department for Terna S.p.A, the Italian transmission grid utility. He is an expert with 40-years' experience on power transformer condition assessment using PD and other technologies.

About the Authors xvii

Preface xix

Acknowledgments xx

Acronyms xxi

1 Introduction 1

1.1 Why Perform Partial Discharge Measurements? 1

1.2 Partial Discharge and Corona 2

1.3 Categories of PD Tests 3

1.3.1 Factory PD Testing 3

1.3.2 Onsite/Off line PD Tests 5

1.3.3 Online PD Testing and Continuous Monitoring 5

1.4 PD Test Standards 6

1.5 History of PD Measurement 7

1.5.1 RIV Test The First Era 7

1.5.2 Analog PD Detection Using Oscilloscopes The Second Era 9

1.5.3 Digitizing, Ultrahigh Frequency, and Post- Processing The Third Era 11

1.5.3.1 Transition to Digital Instruments 11

1.5.3.2 VHF and UHF PD Detection 12

1.5.3.3 Post- Processing of Signals 14

1.6 The Future 15

1.7 Roadmap for the Book 16

References 17

2 Electric Fields and Electrical Breakdown 21

2.1 Electric Fields in High- Voltage Equipment 21

2.1.1 Impact of Electric Field on Partial Discharges 21

2.1.2 Basic Quantities and Equations 21

2.1.3 Simple Electrode Configurations 22

2.1.3.1 Parallel Plates Capacitor 24

2.1.3.2 Coaxial Cylindrical Electrodes 24

2.1.3.3 Concentric Spheres 25

2.1.3.4 Point/Plane Electrodes 25

2.1.4 Multi- Dielectric Systems 25

2.1.4.1 Cavities (Voids) 26

2.1.4.2 Interfaces 28

2.1.4.3 Triple Point (Triple Junction) 29

2.1.5 Floating Metal Objects 30

2.2 Electrical Breakdown 30

2.3 Breakdown in Gases 31

2.3.1 Breakdown in Uniform Fields 31

2.3.2 Breakdown in Divergent Fields 36

2.3.3 Breakdown Under Impulse Voltages the V- t Characteristic 37

2.4 Breakdown in Solids 38

2.4.1 Electrical Treeing 40

2.5 Breakdown in Liquids 41

2.6 Dielectric Strength 43

References 45

3 Physics of Partial Discharge 47

3.1 Introduction 47

3.2 Classification of Partial Discharges 47

3.3 PD Current Pulse Characteristics 48

3.4 Effects of PD 53

3.5 Corona Due to Non- Uniform Electric Fields Around Conductors 55

3.5.1 PD and Corona Polarity 56

3.5.2 Corona AC Phase Position 57

3.5.3 Corona Current Pulse Characteristics 57

3.6 Partial Discharge in Voids 59

3.6.1 PD Inception 59

3.6.1.1 Inception Delay 61

3.6.2 Modified Field Due to Space Charge 62

3.7 PD on Insulation Surfaces 66

3.7.1 Triple Point Junction 66

3.7.2 Electrical Tracking 66

3.8 Effect of Ambient Conditions and Conditioning 67

3.8.1 Conditioning 67

3.8.2 Ambient/Operating Conditions 68

3.9 Summary of Measured PD Quantities 68

3.9.1 Magnitude 69

3.9.2 Pulse Count Rate 69

3.9.3 Phase Position 70

3.10 Understanding the PD Pattern with Respect to the AC Cycle 71

3.10.1 Polarity Analysis 71

3.10.2 Physical Basis for PRPD Patterns 71

3.10.3 PD Packets 80

References 82

4 Other Discharge Phenomena 85

4.1 Introduction 85

4.2 PD as Interference 86

4.3 Circuit Breaker Arcing 87

4.4 Contact Arcing and Intermittent Connections 87

4.5 Metal Oxide Layer Breakdown 89

4.6 Dry Band Arcing 89

4.7 Glow (or Pulseless) Discharge 89

References 90

5 PD Measurement Overview 93

5.1 Introduction 93

5.2 Charge- Based and Electromagnetic Measurement Methods 93

5.3 Optical PD Detection 95

5.4 Acoustic Detection of PD 97

5.4.1 Acoustic Detection of PD Through the Air 98

5.4.2 Acoustic PD Detection Within Enclosed HV Apparatus 102

5.4.2.1 Power Transformers 102

5.4.2.2 Gas- Insulated Switchgear and Isolated Phase Bus 104

5.5 Chemical Detection 105

5.5.1 Ozone in Air 105

5.5.2 Dissolved Gas Analysis (DGA) 106

5.5.3 SF 6 Decomposition Products in GIS 107

References 107

6 Charge- Based PD Detection 109

6.1 Introduction 109

6.2 Basic Electrical Detection Circuits Using Coupling Capacitors 109

6.2.1 Direct Circuit 110

6.2.2 Indirect Circuit 111

6.3 Measuring Impedances 111

6.3.1 Resistors and Quadripoles 111

6.3.2 AC Synchronization and Quadripoles 113

6.3.3 High- Frequency Current Transformers 113

6.4 Electrical PD Detection Models 115

6.4.1 ABC Model 115

6.4.1.1 Equivalent Circuit 117

6.4.1.2 Equivalent PD Current Generator 117

6.4.1.3 Coupling Capacitor 117

6.4.1.4 Under Estimation of Charge 118

6.4.2 Dipole Model 118

6.4.3 Comparing the ABC Model with the Dipole Model 120

6.4.4 Pulse Polarity 120

6.5 Quasi- integration in Charge- Based Measuring Systems 121

6.5.1 Quasi- integration Explained 121

6.5.2 Frequency Range of Charge- Based PD Detectors 122

6.5.2.1 Pros and Cons of the Narrowband vs Wideband Systems 123

6.6 Calibration into Apparent Charge 125

6.6.1 Capacitive Test Objects 125

6.6.2 Distributed Test Objects 126

6.6.2.1 PD Pulse Splitting and Reflections 127

6.6.2.2 Attenuation and Dispersion 129

6.6.3 Inductive- Capacitive Test Objects 132

6.6.4 Practical Calibrators 134

References 135

7 Electromagnetic (RF) PD Detection 137

7.1 Why Measure Electromagnetic Signals from PD 137

7.2 Terminology 139

7.3 Basic Electrical Detection Circuits 141

7.3.1 Transmission Path 141

7.3.2 Sensors 144

7.3.3 Time and Frequency Domain Measurement 145

7.4 Types of RF Sensors 148

7.4.1 Ferrite Antennas 148

7.4.2 Magnetic Loops 148

7.4.3 Transient Earth Voltage (TEV) Sensors 148

7.4.4 Internal or Tank- Mounted UHF Sensors 149

7.4.5 Antennas 150

7.4.5.1 Monopole 150

7.4.5.2 Patch (Microstrip) Antenna 151

7.4.5.3 Horn Antenna 152

7.4.5.4 Stator Slot Couplers 152

7.5 Measuring Instruments 153

7.6 Performance and Sensitivity Check 153

7.7 PD Source Location 155

References 156

8 PD Measurement System Instrumentation and Software 159

8.1 Introduction 159

8.2 Frequency Range Selection 160

8.3 PD Detector Hardware Configurations 160

8.3.1 Minimum Threshold and Processing Time 162

8.3.2 AC Voltage Measurement and Synchronization 163

8.3.3 Combined AnalogDigital Systems 164

8.3.4 Digital System to Measure Pulse Magnitude and Selected Pulse Characteristics 165

8.3.5 Systems to Facilitate Waveform Post- Processing 165

8.4 Hardware- Based Interference Suppression and PD Source Identification 166

8.4.1 Hardware- Based Gating 166

8.4.2 Time- of- Flight (or Time of Arrival) Method 167

8.4.3 Pulse Shape Analysis 169

8.5 PD Calibrator Hardware 170

8.6 Special Hardware Requirements for Continuous Monitors 171

8.6.1 Sensor Reliability 172

8.6.2 Instrument Robustness 173

8.6.3 Cybersecurity 173

8.7 PD System Output Charts 174

8.7.1 Pulse Magnitude Analysis (PMA) Plot 174

8.7.2 Phase- Magnitude- Number (Ø-q- n) Plot 175

8.7.3 Phase- Resolved PD (PRPD) Plot 176

8.7.4 Trend Plot 176

8.7.5 PDIV/PDEV Plot 178

8.7.6 Scatter Plot 179

8.8 PD Activity Indicators 179

8.8.1 Quasi- Peak PD Magnitude (QIEC) 180

8.8.2 Peak PD Magnitude (Qm) 181

8.8.3 Integrated PD Indicators 181

8.9 Post- Processing Software for Interference Suppression and PD Analysis 183

8.9.1 Statistical Post- Processing 183

8.9.2 Time- Frequency Maps 184

8.9.3 Three- Phase Synchronous Pattern Analysis 186

8.9.4 Software- Based Censoring 187

8.9.5 Artificial Intelligence (AI) and Expert Systems 188

References 190

9 Suppression of External Electrical Interference 193

9.1 Impact of External Electrical Interference 193

9.1.1 Factory Testing 193

9.1.2 Condition Assessment Testing 194

9.2 Typical Sources of Noise and External Electrical Interference 194

9.2.1 Electrical/Electronic Noise 194

9.2.2 External Electrical Interference (Disturbances) 195

9.2.2.1 PD and Corona from Connected Equipment 195

9.2.2.2 Arcing from Poorly Bonded Metal and Connections 196

9.2.2.3 Electronic Switching 196

9.2.2.4 Slip Ring/Brush Arcing 197

9.2.2.5 Lighting 197

9.3 Interference Suppression for Off line PD Testing 198

9.3.1 Electromagnetic Shielded Rooms 198

9.3.2 Good Practice for Test Set- Up 198

9.3.3 Power Supply Filtering 199

9.3.4 Signal Filtering 199

9.3.5 PD Measurement Bridges 200

9.3.6 Time- of- Flight 201

9.3.7 PRPD Pattern Recognition 202

9.3.8 Time- Frequency Map 202

9.3.9 Gating 202

9.4 Online Interference Suppression 203

References 203

10 Performing PD Tests and Basic Interpretation 205

10.1 Introduction 205

10.2 PDIV/PDEV Measurement 206

10.2.1 Test Procedure 206

10.2.2 Sensitivity 207

10.2.3 Interpretation 207

References 225

11 PD Testing of Lumped Capacitive Test Objects 227

11.1 Lumped Capacitive Objects 227

11.2 Test Procedures 228

11.3 Measures to Suppress Electrical Interference 230

11.4 Sensitivity Check 231

References 233

12 PD in Power Cables 235

12.1 Introduction 235

12.2 Cable System Structure 235

12.2.1 Cable Insulation 236

References 279

13 Gas-Insulated Switchgear (GIS) 283

13.1 Introduction 283

13.2 Relevant Standards and Technical Guidance 283

13.3 The GIS Insulation System 286

13.3.1 Insulation System Components 286

References 358

14 Air- Insulated Switchgear and Isolated Phase Bus 365

14.1 Introduction 365

14.2 AIS Insulation Systems 366

14.3 Insulation Failure Processes 368

14.3.1 Surface Electrical Tracking 368

References 379

15 Power Transformers 381

15.1 Introduction 381

15.2 Transformer Insulation Systems 382

15.2.1 Dry- Type Transformer 382

15.2.2 Materials Used in Liquid- Filled Paper- Insulated Power Transformers 384

References 452

16 Rotating Machine Stator Windings 457

16.1 Introduction 457

16.2 Relevant Standards 458

16.3 Stator Winding Insulation Systems 458

16.3.1 Insulation System Components 459

16.3.2 PD Suppression Coatings 461

16.3.3 Stator Winding Construction 462

References 501

17 PD Detection in DC Equipment 505

17.1 Why Is HVDC So Popular Now? 505

17.2 Insulation System Design in dc 506

17.3 The Reasons for PD Testing Using dc 507

17.4 Off line PD Testing with DC Excitation 510

17.5 Interpretation of PD Measurements Under DC Excitation 511

17.5.1 Time Series Interpretation 512

17.5.2 Magnitude Dispersion 513

17.5.3 Effect of Operating Conditions on PD 514

17.6 Perspective 517

References 517

18 PD Detection Under Impulse Voltage 519

18.1 Introduction 519

18.2 Insulation Failure Due to Short Risetime Impulse Voltages 520

18.2.1 High Peak Voltage 520

18.2.2 Short Risetime Causing High Turn Voltages in Windings 521

References 531

Index 533