Non-destructive Diagnostic of High Voltage Electrical Systems: Theoretical Analysis and Practical Applications

336 Pages·2023·28.742 MB·English

by  Josef Vedral

Non-destructive Diagnostic of High
Voltage Electrical Systems:
Theoretical Analysis and
Practical Applications
RIVER PUBLISHERS SERIES IN ENERGY ENGINEERING
AND SYSTEMS
Series Editors
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Non-destructive Diagnostic of High
Voltage Electrical Systems:
Theoretical Analysis and
Practical Applications
Josef Vedral
Czech Technical University in Prague, Czech Republic
River Publishers
Published 2023 by River Publishers
River Publishers

Alsbjergvej 10, 9260 Gistrup, Denmark

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Distributed exclusively by Routledge
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Non-destructive Diagnostic of High Voltage Electrical Systems: Theoretical
Analysis and Practical Applications / Josef Vedral.
©2023 River Publishers. All rights reserved. No part of this publication may

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ISBN 978-87-7022-802-2 (print)

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ISBN 978-1-003-39419-8 (ebook master)

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Contents

Preface xiii

List of Figures xv

List of Tables xxv
List of Abbreviations xxvii
1 Introduction 1

2 General View on Diagnostics of Electrical Machines 5

2.1 Diagnosed Object . . . . . . . . . . . . . . . . . . . . . . . 5

2.2 Online and Offline Diagnostic . . . . . . . . . . . . . . . . . 7

2.2.1 Offline diagnostic . . . . . . . . . . . . . . . . . . . 8

2.2.2 Online diagnostic . . . . . . . . . . . . . . . . . . . 9

2.3 Forecast of the Condition of the Diagnosed Device . . . . . . 10

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

3 Diagnostics of Mechanical Parts of HV Machines 13

3.1 Measuring Machine Vibration . . . . . . . . . . . . . . . . . 13

3.1.1 Types of vibrations and vibrodiagnostic quantities . . 13

3.1.2 Vibrometer sensors . . . . . . . . . . . . . . . . . . 15

3.1.2.1 Deflection sensors . . . . . . . . . . . . . . 17

3.1.2.2 Speed sensors . . . . . . . . . . . . . . . . 18

3.1.2.3 Acceleration sensors . . . . . . . . . . . . . 19

3.1.3 Analysis of vibrometric signals . . . . . . . . . . . . 24

3.1.3.1 Analysis of vibrometric signals in the time

domain . . . . . . . . . . . . . . . . . . . . 24

3.1.3.2 Analysis of vibrometric signals in the

frequency domain . . . . . . . . . . . . . . 25

3.2 Torsional Oscillation of Shafts . . . . . . . . . . . . . . . . 33

3.2.1 Causes of shaft torsional oscillation . . . . . . . . . . 33

3.2.2 Measurement of shaft torsional oscillation . . . . . . 35

v
vi Contents
3.3 Measurement of Temperature Images of Electrical Machines 37

3.3.1 Contact temperature sensors . . . . . . . . . . . . . . 39

3.3.2 Non-contact temperature sensors . . . . . . . . . . . 45

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

Author Queries . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

4 Insulation Systems of HV Electric Machines 49

4.1 Electrical Properties of Insulators . . . . . . . . . . . . . . . 49

4.1.1 Electrical strength of insulators . . . . . . . . . . . . 49

4.1.1.1 Electrical strength of gaseous insulators . . 49

4.1.1.2 Electrical strength of liquid insulators . . . . 54

4.1.1.3 Electrical strength of solid insulators . . . . 57

4.1.2 Electrical conductivity of insulators . . . . . . . . . . 59

4.1.2.1 Electrical conductivity of gaseous

insulators. . . . . . . . . . . . . . . . . . . 60

4.1.2.2 Electrical conductivity of liquid

insulators. . . . . . . . . . . . . . . . . . . 60

4.1.2.3 Electrical conductivity of solid

insulators. . . . . . . . . . . . . . . . . . . 63

4.1.3 Polarization of insulators . . . . . . . . . . . . . . . 64

4.1.4 Dielectric losses in insulators . . . . . . . . . . . . . 66

4.1.4.1 Dielectric losses in gaseous insulators . . . 67

4.1.4.2 Dielectric losses in liquid insulators . . . . . 68

4.1.4.3 Dielectric losses in solid insulators . . . . . 68

4.2 Types of Insulators . . . . . . . . . . . . . . . . . . . . . . 69

4.2.1 Gaseous insulators . . . . . . . . . . . . . . . . . . . 70

4.2.2 Liquid insulators . . . . . . . . . . . . . . . . . . . . 71

4.2.3 Solid insulators . . . . . . . . . . . . . . . . . . . . 74

4.3 Electrical Stress on Insulators . . . . . . . . . . . . . . . . . 76

4.3.1 Stress on plate insulators . . . . . . . . . . . . . . . 77

4.3.2 Stress on cylindrical insulators . . . . . . . . . . . . 78

4.4 Degradation of Isolators . . . . . . . . . . . . . . . . . . . . 80

4.4.1 Mechanical aging . . . . . . . . . . . . . . . . . . . 81

4.4.2 Thermal aging . . . . . . . . . . . . . . . . . . . . . 81

4.4.3 Electrical aging . . . . . . . . . . . . . . . . . . . . 84

4.4.4 Combined aging . . . . . . . . . . . . . . . . . . . . 86

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
Contents vii

5 Measurement of Properties of Insulation Systems of

HV Electrical Machines 91

5.1 Measurement of Insulation Current and Resistance . . . . . . 91

5.2 Measurement of Capacity and Loss Factor . . . . . . . . . . 93

5.2.1 Measurement of capacity and loss factor by the

HV Schering bridge . . . . . . . . . . . . . . . . . . 95

5.2.2 Measurement of capacitance and loss factor of

HV impedance meters . . . . . . . . . . . . . . . . . 97

5.2.3 Measurement of frequency dependence of

capacity and loss factor . . . . . . . . . . . . . . . . 102

5.3 Measurement of Dielectric Absorption of Insulation

Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107

6 Partial Discharges in Insulating Systems of

HV Electric Machines 109

6.1 Formation and Types of Partial Discharges . . . . . . . . . . 109

6.2 Partial Discharge Parameters . . . . . . . . . . . . . . . . . 112

6.3 Partial Discharge Models . . . . . . . . . . . . . . . . . . . 117

6.3.1 Model of external and surface partial discharges . . . 117

6.3.2 Gemant–Philippoff model of internal partial

discharges . . . . . . . . . . . . . . . . . . . . . . . 118

6.3.3 Bönings model of internal partial discharges . . . . . 121

6.4 Effect of Partial Discharges on the Insulation Systems of

HV Machines . . . . . . . . . . . . . . . . . . . . . . . . . 123

6.4.1 Electro-erosive effects of partial discharges . . . . . . 124

6.4.2 Chemical effects of partial discharges . . . . . . . . . 124

6.4.3 Thermal effects of partial discharges . . . . . . . . . 125

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125

7 Measurement and Detection of Partial Discharges 129

7.1 Electrical Methods Measurement and Detection of Partial

Discharges . . . . . . . . . . . . . . . . . . . . . . . . . . . 129

7.1.1 Properties of partial discharge current pulses . . . . . 129

7.1.2 Galvanic methods for measuring partial

discharges . . . . . . . . . . . . . . . . . . . . . . . 131

7.1.2.1 Coupling capacitors . . . . . . . . . . . . . 134

7.1.2.2 Coupling impedance . . . . . . . . . . . . . 134
viii Contents
7.1.3 Measurement of partial discharges . . . . . . . . . . 138

7.1.3.1 Measurement of partial discharges with

oscilloscope . . . . . . . . . . . . . . . . . 139

7.1.3.2 Measurement of partial discharges by a

peak detector . . . . . . . . . . . . . . . . . 139

7.1.3.3 Partial discharge meters with direct signal

digitization . . . . . . . . . . . . . . . . . . 142

7.1.4 Charge calibration . . . . . . . . . . . . . . . . . . . 149

7.1.5 Measurement of partial discharges by

current transformers . . . . . . . . . . . . . . . . . . 151

7.1.6 Measurement of partial discharges by inductive

probes . . . . . . . . . . . . . . . . . . . . . . . . . 153

7.1.7 Measurement of partial discharges by capacitive

probes . . . . . . . . . . . . . . . . . . . . . . . . . 156

7.2 Non-electrical Methods for the Detection of Partial

Discharges . . . . . . . . . . . . . . . . . . . . . . . . . . . 159

7.2.1 Ultrasonic detection of partial discharges . . . . . . . 159

7.2.2 High-frequency detection of partial discharges . . . . 162

7.2.3 Optical partial discharges detection . . . . . . . . . . 166

7.2.4 Chemical detection of partial discharges . . . . . . . 167

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170

8 Voltage Tests of HV Electric Machines 173

8.1 DC Voltage Tests . . . . . . . . . . . . . . . . . . . . . . . 173

8.2 AC Voltage Tests . . . . . . . . . . . . . . . . . . . . . . . . 173

8.3 Voltage Tests by Long-term Induced Voltage . . . . . . . . . 174

8.4 Impulse Voltage Tests . . . . . . . . . . . . . . . . . . . . . 174

8.4.1 Course of impulse voltage tests . . . . . . . . . . . . 175

8.4.2 Test pulses . . . . . . . . . . . . . . . . . . . . . . . 175

8.4.3 Generation of test voltage pulses . . . . . . . . . . . 178

8.4.3.1 Single-stage voltage shock generators . . . . 178

8.4.3.2 Multi-stage voltage shock generators . . . . 179

8.4.4 Voltage level impulse tests . . . . . . . . . . . . . . 181

8.4.4.1 Tests with a constant number of voltage

levels . . . . . . . . . . . . . . . . . . . . 182

8.4.4.2 Up–down tests . . . . . . . . . . . . . . . 182

8.4.4.3 Phased stress tests . . . . . . . . . . . . . . 184

8.4.4.4 Statistical methods for the evaluation of

level tests . . . . . . . . . . . . . . . . . . 186

8.5 Shock Wave Tests . . . . . . . . . . . . . . . . . . . . . . . 189

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
Contents ix

9 Diagnostics of Power Transformers 193

9.1 Types of Power Transformers . . . . . . . . . . . . . . . . . 193

9.2 Properties of Transformers . . . . . . . . . . . . . . . . . . 194

9.3 Diagnostics of Electrical Properties of Power

Transformers . . . . . . . . . . . . . . . . . . . . . . . . . . 197

9.3.1 Measurement of active winding resistance . . . . . . 198

9.3.2 Checking the sequence and rotation of the phases . . 200

9.3.3 Measurement of transmission, voltage, and

no-load losses . . . . . . . . . . . . . . . . . . . . . 202

9.3.4 Measurement of short-circuit voltages and losses . . . 204

9.3.5 Measuring the efficiency of transformers . . . . . . . 205

9.3.6 Measurement of insulation resistance, polarization

index, and transformer time constant . . . . . . . . . 210

9.3.7 Measurement of loss factor and winding capacity . . 211

9.3.8 Winding fault detection . . . . . . . . . . . . . . . . 215

9.4 Diagnostics of Transformer Oil Properties . . . . . . . . . . 220

9.4.1 Measurement of electrical properties of

transformer oils . . . . . . . . . . . . . . . . . . . . 221

9.4.1.1 Measurement of breakdown voltage at

mains frequency . . . . . . . . . . . . . . . 221

9.4.1.2 Measurement of relative permittivity and

loss factor . . . . . . . . . . . . . . . . . . 222

9.4.1.3 Measurement of internal resistivity of

transformer oils . . . . . . . . . . . . . . . 224

9.4.2 Measurement of physical properties of

transformer oils . . . . . . . . . . . . . . . . . . . . 225

9.4.2.1 Transformer oil color measurement . . . . . 225

9.4.2.2 Transformer oil density measurement . . . . 225

9.4.2.3 Measuring the viscosity of transformer oils . . 227

9.4.2.4 Measurement of flash and combustion

temperatures . . . . . . . . . . . . . . . . . 228

9.4.2.5 Freezing temperature measurement . . . . . 228

9.4.3 Measurement of chemical properties of

transformer oils . . . . . . . . . . . . . . . . . . . . 229

9.4.3.1 Water content measurement . . . . . . . . . 229

9.4.3.2 Oil acid measurement . . . . . . . . . . . . 231

9.4.3.3 Measurement of the presence of sulfur . . . 232

9.4.3.4 Content of polycyclic aromatics and

polychlorinated biphenyls . . . . . . . . . . 232

9.4.3.5 Gas content measurement . . . . . . . . . . 232

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233