Foreword ix
Preface xi
Acknowledgments xiii
About the Authors xv
Acronyms xvii
List of Figures xxi
List of Tables xxix
1 Power Transformer in a Power Grid 1
1.1 Typical Structure of a Power Transformer 2
1.2 Insulation Oil in a Power Transformer 3
1.3 Condition Monitoring of an Oil-Immersed Power Transformer 7
1.3.1 Temperature 7
1.3.2 Moisture 8
1.3.3 Dissolved Gases Analysis 9
1.3.4 Partial Discharge 10
1.3.5 Combined Online Monitoring 11
1.4 Conclusion 11
References 12
2 Temperature Detection with Optical Methods 15
2.1 Thermal Analysis in a Power Transformer 15
2.1.1 Heat Source in a Power Transformer 15
2.1.2 Heat Transfer in a Power Transformer 16
2.2 Fluorescence-Based Temperature Detection 18
2.2.1 Detection Principle 18
2.2.2 Fabrication and Application 20
2.2.3 Merits and Drawbacks 21
2.3 FBG-Based Temperature Detection 22
2.3.1 Detection Principle 22
2.3.2 Fabrication and Application 24
2.3.3 Merits and Drawbacks 25
2.4 Distribution Measurement 27
2.4.1 Quasi-Distributed Temperature Sensing 27
2.4.2 Distribute Temperature Sensing 28
2.4.2.1 Light Scattering 28
2.4.2.2 Raman Based Distributed Temperature Sensing 28
2.4.2.3 Rayleigh-Based Distributed Temperature Sensing 32
2.4.3 Merits and Drawbacks 33
2.5 Conclusion 33
References 34
3 Moisture Detection with Optical Methods 37
3.1 Online Monitoring of Moisture in a Transformer 37
3.1.1 Distribution of Moisture in the Power Transformer 38
3.1.2 Typical Moisture Detection Techniques 40
3.2 FBG-Based Moisture Detection 42
3.2.1 Detection Principle 42
3.2.2 Fabrication and Application 45
3.2.3 Merits and Drawbacks 48
3.3 Evanescent Wave-Based Moisture Detection 49
3.3.1 Detection Principle 49
3.3.2 Fabrication of MNF 53
3.3.2.1 Chemical Etching Method 53
3.3.2.2 Fused Biconical Taper Method 54
3.3.3 MNF Moisture Detection 56
3.3.4 Merits and Drawbacks 57
3.4 Fabryâ"Perot-Based Moisture Detection 58
3.4.1 Detection Principle 58
3.4.2 Fabrication and Application 59
3.4.3 Merits and Drawbacks 61
3.5 Conclusion 61
References 62
4 Dissolved Gases Detection with Optical Methods 65
4.1 Online Dissolved Gases Analysis 65
4.1.1 General Quantitive Requirements of Online DGA 67
4.1.2 Advantages of Optical Techniques in DGA 70
4.2 Photoacoustic Spectrum Technique 70
4.2.1 Detection Principle of PAS 70
4.2.2 Application of a PAS-Based Technique 73
4.2.3 Merits and Drawbacks 74
4.3 Fourier Transform Infrared Spectroscopy (FTIR) Technique 76
4.3.1 Detection Principle of FTIR 76
4.3.2 Application of the FTIR-Based Techniques 80
4.3.2.1 FTIR Technique 80
4.3.2.2 Online FTIR Application 85
4.3.2.3 Combination of FTIR and PAS 86
4.3.3 Merits and Drawbacks 88
4.4 TDLAS-Based Technique 89
4.4.1 Detection Principle of TDLAS 89
4.4.2 Application of the TDLAS-Based Technique 92
4.4.2.1 Optical Lasers 94
4.4.2.2 Multi-pass Gas Cell 95
4.4.2.3 Topology of Multi-gas Detection 96
4.4.2.4 Laboratory Tests 99
4.4.2.5 Field Application 103
4.4.3 Merits and Drawbacks 105
4.5 Laser Raman Spectroscopy Technique 106
4.5.1 Detection Principle of Raman Spectroscopy 106
4.5.2 Application of Laser Raman Spectroscopy 107
4.5.3 Merits and Drawbacks 109
4.6 Fiber Bragg Grating (FBG) Technique 110
4.6.1 Detection Principle of FBG 110
4.6.2 Application of the FBG Technique 110
4.6.2.1 Standard FBG Sensor 110
4.6.2.2 Etched FBG Sensor 114
4.6.2.3 Side-Polished FBG Sensor 118
4.6.3 Merits and Drawbacks 121
4.7 Discussion and Prediction 123
4.7.1 Comparison of Optical Fiber Techniques 123
4.7.2 Future Prospects of Optic-Based Diagnosis 125
4.8 Conclusions 127
References 128
5 Partial Discharge Detection with Optical Methods 137
5.1 PD Activities in Power Transformers 137
5.1.1 Online PD Detection Techniques 138
5.1.2 PD Induced Acoustic Emission 139
5.2 FBG-Based Detection 142
5.2.1 FBG PD Detection Principle 142
5.2.2 PS-FBG PD Detection 144
5.2.3 High Resolution FBG PD Detection 148
5.2.4 Merits and Drawbacks 149
5.3 FP-Based PD Detection 150
5.3.1 FP-Based Principle 150
5.3.2 Application of FP PD Detection 152
5.3.3 Sensitivity of an FP-Based Sensor 155
5.3.3.1 The Diaphragm Thickness 155
5.3.3.2 The Diaphragm Material 156
5.3.3.3 The Diaphragm Shape 156
5.3.4 Merits and Drawbacks 157
5.4 Dual-Beam Interference-Based PD Detection 158
5.4.1 Principle of Different Interference Structures 158
5.4.1.1 Mach-Zehnder Interference 158
5.4.1.2 Michelson Interference 159
5.4.1.3 Sagnac Interference 160
5.4.2 Application Cases 162
5.4.2.1 PD Detection Based on Mach-Zehnder 162
5.4.2.2 PD Detection Based on Michelson 162
5.4.2.3 PD Detection Based on Sagnac 163
5.4.3 Sensitivity of an Interference-Based Sensor 166
5.4.3.1 Sensor Parameter Variation 166
5.4.3.2 Phase Modulation and Demodulation Techniques 168
5.4.4 Merits and Drawbacks 171
5.5 Multiplexing Technology of an Optical Sensor 171
5.5.1 Multiplexing Technique with the Same Structure 171
5.5.2 Multiplexing Technique with the Different Structures 175
5.5.3 Distributed Optical Sensing Technique 176
5.6 Conclusion 179
References 182
6 Other Parameters with Optical Methods 189
6.1 Winding Deformation and Vibration Detection in Optical Techniques 189
6.1.1 Winding Deformation Detection 189
6.1.1.1 Winding Deformation in Power Transformer 189
6.1.1.2 Winding Deformation Detection with an Optical Technique 190
6.1.2 Vibration Detection 192
6.1.2.1 Vibration in Power Transformers 192
6.1.2.2 Vibration Detection with Optical Techniques 194
6.1.3 Merits and Drawbacks 197
6.2 Voltage and Current Measurement with Optical Techniques 198
6.2.1 Current Measurement with Optical Technique 199
6.2.1.1 Principle of Optical Current Transducer 199
6.2.1.2 All-Fiber Optical Current Transducer 200
6.2.2 Voltage Measurement with the Optical Technique 200
6.2.2.1 Principle of the Optical Voltage Transducer 200
6.2.2.2 All-Fiber Optical Voltage Transducer 202
6.2.3 Merits and Drawbacks 202
6.3 Electric Field Measurement 203
6.4 Conclusion 205
6.5 Outlook 207
6.5.1 Profound and Extensive Interdisciplinary Combinations 208
6.5.2 Mature Scheme and Low Cost Manufacturing 208
6.5.3 Reliable Measurement and Long-Term Stability 208
6.5.4 Pre-factory Installation and Integration into a Monitoring System 209
6.5.5 Rapid Expansion and Development 209
6.5.6 Advanced Algorithms and Novel Diagnosis 210
References 210
Index 213
