Alternative Liquid Dielectrics for High Voltage Transformer Insulation Systems – Performance Analysis and Applications

Mohan Rao Ungarala, PhD, is a postdoctoral fellow at Universit du Qubec Chicoutimi (UQAC), Qubec, Canada with the Research Chair on the Aging of Power Network Infrastructure (ViAHT). He is a member of the IEEE DEIS Technical Committee on Liquid Dielectrics. Issouf Fofana, PhD, is a professor at Universit du Qubec Chicoutimi (UQAC), Quebec, Canada. He is the director of the MODELE laboratory and the International Research Centre on Atmospheric Icing and Power Network Engineering. Ramanujam Sarathi, PhD, is a professor in the Department of Electrical Engineering, IIT Madras, India. He is a senior IEEE member, chair of the IEEE Madras Section PES, a fellow of the Institution of Engineers, India, and a member of the International Reference Group for SweGRIDS, Sweden. Editor Biographies xv List of Contributors xvii Acknowledgments xxi Editorial xxiii 1 Liquid Insulation for Power Transformers 1 U. Mohan Rao, I. Fofana, and E. Rodriguez Celis 1.1 Background of Liquid-Filled Transformers 1 1.2 Insulation System in Liquid-Filled Transformers 3 1.3 Insulation Aging Phenomena in Transformers 4 1.4 Transformer Insulating Liquids 6 1.4.1 Conventional Liquid Dielectrics 6 1.4.1.1 Mineral Insulating Oils 6 1.4.1.2 Polychlorinated Biphenyl 6 1.4.1.3 High-Temperature Hydrocarbons 7 1.4.2 Alternative Liquid Dielectrics 7 1.4.2.1 Natural Ester Liquids 7 1.4.2.2 Vegetable Oils 7 1.4.2.3 Synthetic Ester Liquids 7 References 8 2 Processing and Evaluation of Natural Esters 11 Niharika Baruah, Rohith Sangineni, Mrutyunjay Maharana, and Sisir Kumar Nayak 2.1 Introduction 11 2.2 Significant Natural Ester Liquids 14 2.2.1 Soybean Oil 14 2.2.2 Pongamia Pinnata Oil 14 2.2.3 Jatropha Curcas Oil 15 2.2.4 Palm Oil 15 2.2.5 Rapeseed Oil (Canola Oil) 16 2.3 Processing and Pretreatment 16 2.3.1 Extraction of Oil 16 2.3.1.1 Mechanical Extraction 17 2.3.1.2 Chemical Extraction 17 2.3.2 Transesterification 17 2.4 Properties and Evaluation of Natural Esters 20 2.4.1 Electrical Properties 20 2.4.1.1 AC Breakdown Voltage (ACBDV) 20 2.4.1.2 Dielectric Dissipation Factor (DDF) 21 2.4.1.3 Dielectric Constant 23 2.4.2 Chemical Properties 23 2.4.2.1 Water Content 23 2.4.2.2 Sulphur Content 24 2.4.2.3 Total Acid Number (TAN) 24 2.4.2.4 Oxidation Stability 24 2.4.3 Physical Properties 25 2.4.3.1 Pour Point 25 2.4.3.2 Flash and Fire Point 26 2.4.3.3 Interfacial Tension (IFT) 26 2.4.3.4 Thermal Conductivity 26 2.4.3.5 Viscosity 27 2.5 Degradation of Different Vegetable Oils 27 2.5.1 Fourier Transform Infrared Spectroscopy (FTIR) 29 2.5.2 Nuclear Magnetic Resonance (NMR) Study 30 2.6 Dissolved Gas Analysis in Natural Esters 31 2.6.1 Standard Gas Ratios 32 2.6.1.1 IEC Gas Ratios 32 2.6.1.2 Doernenburg Ratio Method 32 2.6.1.3 Rogers Ratio Method 34 2.6.1.4 Duval’s Triangle 34 2.7 Challenges in Using Natural Esters as Insulating Liquid 35 2.8 Conclusions and Future Scope 37 References 38 3 Compatibility of Esters with Cellulosic Insulation Materials 43 Cristina Mndez Gutirrez, Carmela Oria Alonso, Cristina Fernndez Diego, Inmaculada Fernndez Diego, Cristian Olmo Salas, Ahmet Kerem Kseolu, Ramazan Altay, and Alfredo Ortiz Fernndez 3.1 Introduction 43 3.1.1 Types of Solid Insulation 43 3.1.1.1 Classification According to Manufacturing Processes 43 3.1.1.2 Special Types of Paper Insulation 44 3.1.2 Mechanisms of Paper Degradation 45 3.1.2.1 Processes That Cause Degradation of the Cellulosic Insulation 45 3.1.2.2 Degradation Products from Cellulosic Insulation 46 3.1.3 Effect of Paper Deterioration on Transformer Performance 47 3.2 Procedure of Accelerated Thermal Aging 48 3.2.1 IEEE Std. C57.100 48 3.2.2 IEC 60216 49 3.2.3 Accelerated Thermal Aging Conditions 50 3.2.3.1 Temperature 50 3.2.3.2 Atmosphere 50 3.2.3.3 Moisture 50 3.2.3.4 Other Materials 51 3.2.3.5 Electrical Stress 52 3.3 Assessment of Liquid Degradation 52 3.3.1 Physicochemical Properties 52 3.3.2 Dielectric Properties 53 3.4 Assessment of Paper Degradation 55 3.4.1 Chemical Properties 55 3.4.1.1 Moisture Content 55 3.4.1.2 Degree of Polymerization 55 3.4.1.3 Fourier Transform Infrared Spectroscopy and X-ray Spectroscopy 58 3.4.1.4 Furanic Compounds, Methanol Content, and Gases Production 58 3.4.2 Mechanical Properties 59 3.4.2.1 Tensile Strength 59 3.4.2.2 Relationship Between Degree of Polymerization (DP) and Mechanical Properties 62 3.4.2.3 Scanning Electron Microscope (SEM) 62 3.4.2.4 Refractive Index of Cellulose Fibers (RI) 63 3.4.3 Dielectric Properties 64 3.4.3.1 Breakdown Voltage 64 3.4.3.2 Partial Discharges 65 3.4.3.3 Dielectric Loss Factor 65 3.4.3.4 Dielectric Permittivity 65 3.4.3.5 Conductivity 66 3.4.3.6 Polarization and Depolarization Currents 66 3.5 Remaining Life of Transformer Insulation 66 3.5.1 IEEE C57.91 67 3.5.2 IEC 60076-7 69 3.5.3 Kinetic Approach to Modeling 71 3.5.3.1 Polymerization Degree 71 3.5.3.2 Tensile Strength 73 3.6 Conclusions 76 References 78 4 Degradation Assessment of Ester Liquids 85 A.J. Amalanathan, R. Sarathi, N. Harid, and H. Griffiths 4.1 Introduction 85 4.1.1 Types of Ester Fluids 85 4.1.2 Properties of Ester Fluids 86 4.1.2.1 Breakdown Voltage 87 4.1.2.2 Moisture Content 89 4.1.2.3 Flash Point and Fire Point 90 4.1.2.4 Viscosity 90 4.1.2.5 Oxidation Stability 91 4.1.2.6 Dielectric Constant and Dissipation Factor 91 4.1.2.7 Biodegradability 92 4.1.3 Fluid Maintenance and Storage Issues 92 4.2 Procedure of Accelerated Thermal Aging 93 4.2.1 ASTM D1934-95 93 4.2.2 IEC 62332-2 93 4.2.3 Temperature 94 4.2.4 Atmosphere 94 4.2.5 Moisture 94 4.3 Assessment of Liquid Degradation 95 4.3.1 Partial Discharge Inception Voltage 95 4.3.1.1 Measurement of PDIV Under AC and DC Voltage 96 4.3.1.2 Measurement of PDIV Under Harmonic Voltage 97 4.3.2 Flow Electrification 98 4.3.2.1 Flow Electrification Measurement Methods 98 4.3.3 Spectroscopic Studies 102 4.3.3.1 UV-Visible Spectroscopy 103 4.3.3.2 Fluorescence Spectroscopy 104 4.3.4 Dielectric Response Spectroscopy 107 4.3.5 Physico-Chemical Studies 108 4.3.5.1 Interfacial Tension 108 4.3.5.2 Turbidity 109 4.3.5.3 Viscosity 109 4.3.5.4 Organic Composition of Oil Using GC-MS 110 4.4 Assessment of Paper Degradation 110 4.4.1 Surface Discharge Analysis 111 4.4.2 Surface Potential Measurement 112 4.4.3 Impedance Spectroscopy 113 4.4.4 Py-GC/ MS 116 4.4.5 Laser-Induced Breakdown Spectroscopy 117 4.5 Conclusions and Future Scope 120 References 120 5 End Life Behavior of Ester Liquids in High-Voltage Transformers 127 U. Mohan Rao, I. Fofana, L. Loiselle, and T. Jayasree 5.1 Introduction 127 5.2 Evolution of Colloidal and Soluble Decay Particles 128 5.2.1 Perspective of Decay Particles 128 5.2.2 Size and Influence of Decay Particles 129 5.3 Colloidal Particles – Centrifugal Treatment (ASTM D1698) 130 5.3.1 UV Spectroscopy 132 5.3.2 Turbidity 133 5.3.3 Particle Counter 135 5.4 Soluble Particles – Fuller’s Earth Filtration (ASTM D7150) 137 5.4.1 UV Spectroscopy 137 5.4.2 Turbidity 138 5.4.3 Particle Counter 139 5.5 Feasibility of Fuller’s Earth Filtration for Ester Liquids 140 5.5.1 On Ratio of Fuller’s Earth to Liquid 141 5.5.2 On Treatment Temperature 142 5.6 Conclusions and Future Scope 144 References 145 6 Prebreakdown and Breakdown Phenomena in Ester Dielectric Liquids 147 Pawel Rozga, T. Jayasree, U. Mohan Rao, I. Fofana, and P. Picher 6.1 Introduction 147 6.2 Research Methods in Assessment of Prebreakdown Phenomena in Ester Liquids 148 6.2.1 Standard-Based Approach 149 6.2.2 Experimental Approach 149 6.3 Initiation of Streamers in Dielectric Liquids 150 6.3.1 Influence of Tip Radius on Streamer Initiation 151 6.3.2 Streamer Initiation Mechanisms 153 6.3.3 Research Progress on Streamer Initiation in Esters vs. Mineral Oil 155 6.4 Streamer Propagation 156 6.4.1 Overview of Propagation Modes 156 6.4.2 Streamer Development Theories 162 6.4.3 Streamer Propagation and Breakdown in Esters vs. Mineral Oils 167 6.4.4 Influence of Nanoparticles on Prebreakdown Phenomena in Ester Liquids 172 6.5 Influence of Temperature on Prebreakdown Phenomena in Natural Ester Liquids 173 6.6 Influence of Thermal Aging on Prebreakdown Phenomena in Synthetic Ester Liquids 176 6.7 Conclusions and Future Scope 177 References 178 7 Miscibility and Engineering Application of a Novel Mixed Fluid 185 Jian Hao, Ruijin Liao, Lijun Yang, Dawei Feng, Wenyu Ye, Chenyu Gao, and Xin Chen 7.1 Introduction 185 7.2 Need and Research Progress of Mixed Insulating Liquids 186 7.3 Preparation Method for the New Mixed Insulating Oil 187 7.3.1 Selection of the Base Oil 187 7.3.2 Determination of the Proportion 188 7.3.3 Improvement of Oxidation Stability 189 7.3.4 Stability Overall Performance 189 7.3.5 Performance of Novel Three-Element Mixed Insulating Oil 191 7.4 Thermal Aging Characteristics of the New Mixed Insulation Oil-Paper Insulation and Its Delaying Thermal Aging Mechanism 193 7.4.1 Introduction 193 7.4.2 DP Values of Cellulose Paper 195 7.4.3 Mechanism of Delaying Thermal Aging 199 7.5 Mechanism of Property Enhancement of the New Mixed Insulation Oil on Power Frequency Breakdown of Oil-Paper Insulation 203 7.5.1 Introduction 203 7.5.2 Oils Breakdown Voltage with Different Moisture Contents 204 7.5.3 Oils Breakdown Voltage with Different Temperatures 205 7.5.4 Oil Breakdown Voltage Under Combined Effects of Moisture and Temperature 206 7.5.5 Comparison of AC Breakdown Characteristics of Composite Insulation with Different Temperatures and Moisture Contents 208 7.5.6 Comparison of AC Breakdown Characteristics of Composite Insulation with Oil Gap 212 7.6 Enhancing Effect and Mechanism of the New Mixed Insulation Oil on Flashover Voltage of Oil-Paper Insulation 214 7.6.1 Introduction 214 7.6.2 Surface Flashover Voltage of Oil-Cellulose Insulation Pressboard 215 7.6.3 Surface Flashover Difference Analysis 218 7.7 Application of the New Mixed Insulation Oil: Service Experiences 221 7.7.1 Introduction 221 7.7.2 Using the New Three-Element Mixed Insulation Oil in 10 kV Transformer 222 7.7.3 Overheating and Discharge Fault Identification for Novel Three-Element Mixed Oil-Paper Insulation System 222 7.7.4 Fault-Type Identification Model Based on Hydrogen, Ethane, and Acetylene 231 7.8 Conclusions and Future Scope 233 References 236 8 Natural Ester Nanosfluids as Alternate Insulating Oils for Transformers 241 Joyce Jacob, Preetha Prabhu, and Sindhu Thiruthi Krishnan 8.1 Introduction 241 8.1.1 Importance of Nanofluids 241 8.1.2 Improvement of Natural Esters 242 8.1.2.1 Additives for Chemical Structure Modification 242 8.1.2.2 Addition of Nanoparticles 244 8.1.3 Commonly Used Nanoparticles 244 8.2 Preparation of Natural Ester Nanofluids and Stability Analysis 245 8.2.1 Preparation of Natural Ester Nanofluids 245 8.2.1.1 Different Methods of Nanofluid Preparation 245 8.2.2 Stability of Natural Ester Nanofluids 248 8.2.2.1 Stability of Nanofluids 248 8.2.2.2 Methods of Stability Improvement of Natural Ester Nanofluids 250 8.2.2.3 Methods of Stability Analysis of Natural Ester Nanofluids 252 8.3 Properties of Natural Esters and Natural Ester Nanofluids 254 8.3.1 Physical Properties 254 8.3.2 Electrical Properties 254 8.3.2.1 Permittivity of Nanofluids 254 8.3.2.2 Partial Discharge and Breakdown Voltage in Nanofluids 258 8.3.3 Thermal Properties 261 8.3.4 Aging Study of Natural Ester Nanofluids 263 8.3.5 Feasibility of Natural Ester Nanofluids as an Alternate Insulating Oil for Transformers 266 8.4 Conclusion 267 8.4.1 Stability Enhancement of Natural Ester Nanofluids 267 8.4.2 Simulation Model for Nanofluids 268 8.4.3 Design of Transformers Using Natural Ester Nanofluids 268 8.4.4 Mixed Fluids and Multiparticle Nanofluids 268 References 268 9 Dielectric Properties of Silica-Based Synthetic Ester Nanofluid 273 G. D. P. Mahidhar, R. Sarathi, Nathaniel Taylor, and Hans Edin 9.1 Introduction 273 9.1.1 Need for Nanofluids 274 9.1.2 Methods of Property Enhancement of Nanofluids 274 9.2 Nanofluid Preparation and Characterization 277 9.2.1 Nanoparticle Characterization 277 9.2.2 Nanofluid Preparation 278 9.2.3 Nanofluid Stability 279 9.2.3.1 Particle Size Analysis 279 9.2.3.2 Zeta Potential Analysis 281 9.2.3.3 Viscosity Measurement 281 9.3 Frequency Domain Dielectric Response 282 9.3.1 Experimental Setup 282 9.3.2 Dielectric Constant 283 9.3.3 Dissipation Factor 283 9.4 Time Domain Dielectric Response 285 9.4.1 Experimental Setup 285 9.4.2 Ion Mobility 286 9.4.3 Conductivity and Other Dielectric Properties 289 9.5 Conduction at High Electric Field 290 9.5.1 Experimental Setup 290 9.5.2 I-U Characteristics 291 9.6 Corona Inception Voltage 293 9.6.1 Experimental Setup 293 9.6.2 CIV Results and Discussion 294 9.6.3 Incipient Discharge Activity 296 9.6.3.1 Corona Discharge Activity Under Harmonic AC Voltages 296 9.6.3.2 UHF Signal Energy Analysis 297 9.7 Conclusions and Future Scope 298 References 300 10 Behavior of Ester Liquids Under Various Operating Fault Conditions 305 U. Mohan Rao, I. Fofana, and L. Loiselle 10.1 Introduction 305 10.2 Dissolved Gas Analysis and Transformer Faults 306 10.2.1 Duval’s Triangle 307 10.2.2 Duval’s Pentagon 308 10.2.3 Research Progress on Various Faulty Conditions 308 10.3 Simulation of Various Faults in Laboratory Environment 310 10.3.1 Low-Energy Discharges (Surface Discharges) 310 10.3.2 Thermal Faults (Hotspot) 310 10.3.3 High-Energy Discharges (Arcing) 311 10.4 Influence of Different Faults on the State of Liquid and Gassing Tendency 311 10.4.1 Effect on Gassing Tendency 314 10.4.2 Effect on Degradation 315 10.5 Conclusions and Future Scope 318 References 319 11 In-Service Performance of Natural Esters 321 D. Martin and L. McPherson 11.1 Introduction 321 11.2 Reasons Why These Utilities Chose a Natural Ester 322 11.3 Transformers Under Study 322 11.4 Summary of Research Applied to Manage These Transformers 323 11.5 Fluid Temperature at Rated Load 324 11.6 Breakdown Voltage and Water Content 325 11.7 Investigations into Oxidation and Handling Fluid-Impregnated Paper 326 11.8 Study on Installation and Early Operation of a Power Transformer Filled with Natural Ester 330 11.9 Fleet Measurements 333 11.9.1 Dielectric Dissipation Factor, Interfacial Tension, and Acid Number 334 11.9.2 Water Content of Oil 334 11.9.3 Breakdown Voltage of Oil 336 11.9.4 Dissolved Gas Analysis 337 11.9.5 Electrical Testing of Transformers 338 11.10 Summary 341 References 342 Index 345