Optical Sensing 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 ixPreface xiAcknowledgments xiiiAbout the Authors xvAcronyms xviiList of Figures xxiList of Tables xxix1 Power Transformer in a Power Grid 11.1 Typical Structure of a Power Transformer 21.2 Insulation Oil in a Power Transformer 31.3 Condition Monitoring of an Oil-Immersed Power Transformer 71.3.1 Temperature 71.3.2 Moisture 81.3.3 Dissolved Gases Analysis 91.3.4 Partial Discharge 101.3.5 Combined Online Monitoring 111.4 Conclusion 11References 122 Temperature Detection with Optical Methods 152.1 Thermal Analysis in a Power Transformer 152.1.1 Heat Source in a Power Transformer 152.1.2 Heat Transfer in a Power Transformer 162.2 Fluorescence-Based Temperature Detection 182.2.1 Detection Principle 182.2.2 Fabrication and Application 202.2.3 Merits and Drawbacks 212.3 FBG-Based Temperature Detection 222.3.1 Detection Principle 222.3.2 Fabrication and Application 242.3.3 Merits and Drawbacks 252.4 Distribution Measurement 272.4.1 Quasi-Distributed Temperature Sensing 272.4.2 Distribute Temperature Sensing 282.4.2.1 Light Scattering 282.4.2.2 Raman Based Distributed Temperature Sensing 282.4.2.3 Rayleigh-Based Distributed Temperature Sensing 322.4.3 Merits and Drawbacks 332.5 Conclusion 33References 343 Moisture Detection with Optical Methods 373.1 Online Monitoring of Moisture in a Transformer 373.1.1 Distribution of Moisture in the Power Transformer 383.1.2 Typical Moisture Detection Techniques 403.2 FBG-Based Moisture Detection 423.2.1 Detection Principle 423.2.2 Fabrication and Application 453.2.3 Merits and Drawbacks 483.3 Evanescent Wave-Based Moisture Detection 493.3.1 Detection Principle 493.3.2 Fabrication of MNF 533.3.2.1 Chemical Etching Method 533.3.2.2 Fused Biconical Taper Method 543.3.3 MNF Moisture Detection 563.3.4 Merits and Drawbacks 573.4 Fabry–Perot-Based Moisture Detection 583.4.1 Detection Principle 583.4.2 Fabrication and Application 593.4.3 Merits and Drawbacks 613.5 Conclusion 61References 624 Dissolved Gases Detection with Optical Methods 654.1 Online Dissolved Gases Analysis 654.1.1 General Quantitive Requirements of Online DGA 674.1.2 Advantages of Optical Techniques in DGA 704.2 Photoacoustic Spectrum Technique 704.2.1 Detection Principle of PAS 704.2.2 Application of a PAS-Based Technique 734.2.3 Merits and Drawbacks 744.3 Fourier Transform Infrared Spectroscopy (FTIR) Technique 764.3.1 Detection Principle of FTIR 764.3.2 Application of the FTIR-Based Techniques 804.3.2.1 FTIR Technique 804.3.2.2 Online FTIR Application 854.3.2.3 Combination of FTIR and PAS 864.3.3 Merits and Drawbacks 884.4 TDLAS-Based Technique 894.4.1 Detection Principle of TDLAS 894.4.2 Application of the TDLAS-Based Technique 924.4.2.1 Optical Lasers 944.4.2.2 Multi-pass Gas Cell 954.4.2.3 Topology of Multi-gas Detection 964.4.2.4 Laboratory Tests 994.4.2.5 Field Application 1034.4.3 Merits and Drawbacks 1054.5 Laser Raman Spectroscopy Technique 1064.5.1 Detection Principle of Raman Spectroscopy 1064.5.2 Application of Laser Raman Spectroscopy 1074.5.3 Merits and Drawbacks 1094.6 Fiber Bragg Grating (FBG) Technique 1104.6.1 Detection Principle of FBG 1104.6.2 Application of the FBG Technique 1104.6.2.1 Standard FBG Sensor 1104.6.2.2 Etched FBG Sensor 1144.6.2.3 Side-Polished FBG Sensor 1184.6.3 Merits and Drawbacks 1214.7 Discussion and Prediction 1234.7.1 Comparison of Optical Fiber Techniques 1234.7.2 Future Prospects of Optic-Based Diagnosis 1254.8 Conclusions 127References 1285 Partial Discharge Detection with Optical Methods 1375.1 PD Activities in Power Transformers 1375.1.1 Online PD Detection Techniques 1385.1.2 PD Induced Acoustic Emission 1395.2 FBG-Based Detection 1425.2.1 FBG PD Detection Principle 1425.2.2 PS-FBG PD Detection 1445.2.3 High Resolution FBG PD Detection 1485.2.4 Merits and Drawbacks 1495.3 FP-Based PD Detection 1505.3.1 FP-Based Principle 1505.3.2 Application of FP PD Detection 1525.3.3 Sensitivity of an FP-Based Sensor 1555.3.3.1 The Diaphragm Thickness 1555.3.3.2 The Diaphragm Material 1565.3.3.3 The Diaphragm Shape 1565.3.4 Merits and Drawbacks 1575.4 Dual-Beam Interference-Based PD Detection 1585.4.1 Principle of Different Interference Structures 1585.4.1.1 Mach-Zehnder Interference 1585.4.1.2 Michelson Interference 1595.4.1.3 Sagnac Interference 1605.4.2 Application Cases 1625.4.2.1 PD Detection Based on Mach-Zehnder 1625.4.2.2 PD Detection Based on Michelson 1625.4.2.3 PD Detection Based on Sagnac 1635.4.3 Sensitivity of an Interference-Based Sensor 1665.4.3.1 Sensor Parameter Variation 1665.4.3.2 Phase Modulation and Demodulation Techniques 1685.4.4 Merits and Drawbacks 1715.5 Multiplexing Technology of an Optical Sensor 1715.5.1 Multiplexing Technique with the Same Structure 1715.5.2 Multiplexing Technique with the Different Structures 1755.5.3 Distributed Optical Sensing Technique 1765.6 Conclusion 179References 1826 Other Parameters with Optical Methods 1896.1 Winding Deformation and Vibration Detection in Optical Techniques 1896.1.1 Winding Deformation Detection 1896.1.1.1 Winding Deformation in Power Transformer 1896.1.1.2 Winding Deformation Detection with an Optical Technique 1906.1.2 Vibration Detection 1926.1.2.1 Vibration in Power Transformers 1926.1.2.2 Vibration Detection with Optical Techniques 1946.1.3 Merits and Drawbacks 1976.2 Voltage and Current Measurement with Optical Techniques 1986.2.1 Current Measurement with Optical Technique 1996.2.1.1 Principle of Optical Current Transducer 1996.2.1.2 All-Fiber Optical Current Transducer 2006.2.2 Voltage Measurement with the Optical Technique 2006.2.2.1 Principle of the Optical Voltage Transducer 2006.2.2.2 All-Fiber Optical Voltage Transducer 2026.2.3 Merits and Drawbacks 2026.3 Electric Field Measurement 2036.4 Conclusion 2056.5 Outlook 2076.5.1 Profound and Extensive Interdisciplinary Combinations 2086.5.2 Mature Scheme and Low Cost Manufacturing 2086.5.3 Reliable Measurement and Long-Term Stability 2086.5.4 Pre-factory Installation and Integration into a Monitoring System 2096.5.5 Rapid Expansion and Development 2096.5.6 Advanced Algorithms and Novel Diagnosis 210References 210Index 213