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 Analog–Digital 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 (Q IEC) 180
8.8.2 Peak PD Magnitude (Q m) 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
