Optical Sensing in Power Transformers

A cutting-edge, advanced level, exploration of optical sensing application in power transformers

Optical Sensing in Power Transformers is filled with the critical information and knowledge on the optical techniques applied in power transformers, which are important and expensive components in the electric power system. Effective monitoring of systems has proven to decrease the transformer lifecycle cost and increase a high level of availability and reliability. It is commonly held that optical sensing techniques will play an increasingly significant role in online monitoring of power transformers.

In this comprehensive text, the authors—noted experts on the topic—present a scholarly review of the various cutting-edge optical principles and methodologies adopted for online monitoring of power transformers. Grounded in the authors' extensive research, the book examines optical techniques and high-voltage equipment testing and provides the foundation for further application, prototype, and manufacturing. The book explores the principles, installation, operation, condition detection, monitoring, and fault diagnosis of power transformers. This important text:

• Provides a current exploration of optical sensing application in power transformers
• Examines the critical balance and pros and cons of cost and quality of various optical condition monitoring techniques
• Presents a wide selection of techniques with appropriate technical background
• Extends the vision of condition monitoring testing and analysis
• Treats condition monitoring testing and analysis tools together in a coherent framework

Written for researchers, technical research and development personnel, manufacturers, and frontline engineers, Optical Sensing in Power Transformers offers an up-to-date review of the most recent developments of optical sensing application in power transformers.

Jun Jiang, PhD, is Associate Professor, Department of Electrical Engineering, Nanjing University of Aeronautics and Astronautics, China.   

Guoming Ma, PhD, is Professor, State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources, North China Electric Power University, China.   

Foreword xiii

Preface xiv

Acknowledgments xv

About the Authors

Acronyms xvii

List of Figures vi

List of Tables xi

1 Power Transformer in Power Grid 1

1.1 Typical structure of power transformer 2

1.2 Insulation oil in power transformer 3

1.3 Condition monitoring of oil-immersed power transformer 6

1.3.1 Temperature 7

1.3.2 Moisture 8

1.3.3 Dissolved gases analysis 8

1.3.4 Partial discharge 9

1.3.5 Combined online monitoring 10

1.4 Conclusion 10

References 12

2 Temperature Detection with Optical Methods 16

2.1 Thermal Analysis in Power Transformer 16

2.1.1 Heat Source in Power Transformer 16

2.1.2 Heat transfer in power transformer 17

2.2 Fluorescence-Based Temperature Detection 19

2.2.1 Detection principle 19

2.2.2 Fabrication and application 21

2.2.3 Merits and Drawbacks 22

2.3 FBG-based temperature detection 23

2.3.1 Detection principle 23

2.3.2 Fabrication and application 24

2.3.3 Merits and drawbacks 26

2.4 Distribution Measurement 26

2.4.1 Quasi-distributed temperature sensing 26

2.4.2 Distribute temperature sensing 27

2.3.4 Merits and drawbacks 32

2.5 Conclusion 33

References 35

3 Moisture Detection with Optical Methods 41

3.1 Online monitoring of moisture-in-transformer 41

3.1.1 Distribution of moisture in power transformer 41

3.1.2 Typical moisture detection techniques 44

3.2 FBG-based moisture detection 46

3.2.1 Detection principle 46

3.2.2 Fabrication and application 49

3.2.3 Merits and drawbacks 52

3.3 Evanescent wave based moisture detection 53

3.3.1 Detection principle 53

3.3.2 Fabrication of MNF 57

3.3.3 MNF moisture detection 59

3.3.4 Merits and drawbacks 61

3.4 Fabry-Perot based moisture detection 61

3.4.1 Detection principle 61

3.4.2 Fabrication and application 63

3.4.3 Merits and drawbacks 64

3.5 Conclusion 64

References 66

4 Dissolved Gases Detection with Optical Methods 75

4.1 Online Dissolved gases analysis 75

4.1.1 General quantitive requirements of online DGA 77

4.1.2 Advantages of optical techniques in DGA 79

4.2 Photoacoustic spectrum technique 80

4.2.1 Detection principle of PAS 80

4.2.2 Application of PAS-based technique 82

4.2.3 Merits and drawbacks 84

4.3 Fourier Transform Infrared Spectroscopy (FTIR) technique 85

4.3.1 Detection principle of FTIR 85

4.3.2 Application of FTIR-based technique 90

4.3.3 Merits and drawbacks 98

4.4 TDLAS-based technique 99

4.4.1 Detection principle of TDLAS 99

4.4.2 Application of TDLAS-based technique 101

4.4.3 Merits and drawbacks 113

4.5 Laser Raman spectroscopy technique 113

4.5.1 Detection principle of Raman spectroscopy 113

4.5.2 Application of Laser Raman spectroscopy 114

4.5.3 Merits and drawbacks 117

4.6 Fiber Bragg Grating (FBG) technique 117

4.6.1 Detection principle of FBG 117

4.6.2 Application of FBG technique 118

4.6.3 Merits and drawbacks 131

4.7 Discussion and prediction 132

4.7.1 Comparison of optical fiber techniques 132

4.7.2 Future prospects of optic-based diagnosis 134

4.8 Conclusions 135

Reference 137

5 Partial Discharge Detection with Optical Methods 157

5.1 PD activities in power transformers 157

5.1.1 Online PD detection techniques 158

5.1.2 PD induced acoustic emission 159

5.2 FBG-based detection 161

5.2.1 FBG PD detection principle 161

5.2.2 PS-FBG PD detection 163

5.2.3 High-Resolution FBG PD detection 167

5.2.4 Merits and drawbacks 169

5.3 FP-based PD Detection 170

5.3.1 FP-based principle 170

5.3.2 Application of FP PD detection 172

5.3.3 Sensitivity of FP-based sensor 174

5.3.4 Merits and drawbacks 176

5.4 Dual-beam Interference-based PD Detection 177

5.4.1 Principle of different interference structures 177

5.4.2 Application cases 181

5.4.3 Sensitivity of Interference-based Sensor 185

5.4.4 Merits and drawbacks 190

5.5 Multiplexing technology of optical sensor 190

5.5.1 Multiplexing technique with the same structure 190

5.5.2 Multiplexing technique with the different structures 194

5.5.3 Distributed optical sensing technique 195

5.6 Conclusion 198

References 200

References 222

6 Other Parameters with Optical Methods 223

6.1 Winging deformation and vibration detection in optical techniques 223

6.1.1 Wingding deformation detection 223

6.1.2 Vibration detection 226

6.1.3 Merits and drawbacks 232

6.2 Voltage and current measurement with optical techniques 232

6.2.1 Current measurement with optical technique 233

6.2.2 Voltage measurement with optical technique 235

6.2.3 Merits and drawbacks 237

6.3 Electric field measurement 238

6.4 Conclusion 240

6.5 Outlook 240

References 245

Index 252

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