Alternative Liquid Dielectrics for High Voltage Transformer Insulation Systems

U. Mohan Rao, PhD, Senior Member IEEE, is a Postdoctoral Fellow at Université du Québec à Chicoutimi (UQAC), Québec, Canada, with the Research Chair on the Aging of Power Network Infrastructure. He also serves as the Secretary of the IEEE DEIS Technical Committee on Liquid Dielectrics.I. Fofana, PhD, Fellow IET, is holder of the Research Chair on the Aging of Power Network Infrastructure and Director of the International Research Centre on Atmospheric Icing and Power Engineering at UQAC. He is also chair of the IEEE DEIS Technical Committee on Liquids Dielectrics.R. Sarathi, PhD, is a Professor in the Department of Electrical Engineering, IIT Madras, India. He is a Senior IEEE Member, Fellow INAE, FRSc, Fellow IET, Fellow I(E) India, and a member of the International Reference Group for SweGRIDS, Sweden.

• Editor Biographies xvList of Contributors xviiAcknowledgments xxiEditorial xxiii1 Liquid Insulation for Power Transformers 1U. Mohan Rao, I. Fofana, and E. Rodriguez Celis1.1 Background of Liquid- Filled Transformers 11.2 Insulation System in Liquid- Filled Transformers 31.3 Insulation Aging Phenomena in Transformers 41.4 Transformer Insulating Liquids 61.4.1 Conventional Liquid Dielectrics 61.4.1.1 Mineral Insulating Oils 61.4.1.2 Polychlorinated Biphenyl 61.4.1.3 High- Temperature Hydrocarbons 71.4.2 Alternative Liquid Dielectrics 71.4.2.1 Natural Ester Liquids 71.4.2.2 Vegetable Oils 71.4.2.3 Synthetic Ester Liquids 7References 82 Processing and Evaluation of Natural Esters 11Niharika Baruah, Rohith Sangineni, Mrutyunjay Maharana, and Sisir Kumar Nayak2.1 Introduction 112.2 Significant Natural Ester Liquids 142.2.1 Soybean Oil 142.2.2 Pongamia Pinnata Oil 142.2.3 Jatropha Curcas Oil 152.2.4 Palm Oil 152.2.5 Rapeseed Oil (Canola Oil) 162.3 Processing and Pretreatment 162.3.1 Extraction of Oil 162.3.1.1 Mechanical Extraction 172.3.1.2 Chemical Extraction 172.3.2 Transesterification 172.4 Properties and Evaluation of Natural Esters 202.4.1 Electrical Properties 202.4.1.1 AC Breakdown Voltage (ACBDV) 202.4.1.2 Dielectric Dissipation Factor (DDF) 212.4.1.3 Dielectric Constant 232.4.2 Chemical Properties 232.4.2.1 Water Content 232.4.2.2 Sulphur Content 242.4.2.3 Total Acid Number (TAN) 242.4.2.4 Oxidation Stability 242.4.3 Physical Properties 252.4.3.1 Pour Point 252.4.3.2 Flash and Fire Point 262.4.3.3 Interfacial Tension (IFT) 262.4.3.4 Thermal Conductivity 262.4.3.5 Viscosity 272.5 Degradation of Different Vegetable Oils 272.5.1 Fourier Transform Infrared Spectroscopy (FTIR) 292.5.2 Nuclear Magnetic Resonance (NMR) Study 302.6 Dissolved Gas Analysis in Natural Esters 312.6.1 Standard Gas Ratios 322.6.1.1 IEC Gas Ratios 322.6.1.2 Doernenburg Ratio Method 322.6.1.3 Rogers Ratio Method 342.6.1.4 Duval’s Triangle 342.7 Challenges in Using Natural Esters as Insulating Liquid 352.8 Conclusions and Future Scope 37References 383 Compatibility of Esters with Cellulosic Insulation Materials 43Cristina Méndez Gutiérrez, Carmela Oria Alonso, Cristina Fernández Diego, Inmaculada Fernández Diego, Cristian Olmo Salas, Ahmet Kerem Köseoğlu, Ramazan Altay, and Alfredo Ortiz Fernández3.1 Introduction 433.1.1 Types of Solid Insulation 433.1.1.1 Classification According to Manufacturing Processes 433.1.1.2 Special Types of Paper Insulation 443.1.2 Mechanisms of Paper Degradation 453.1.2.1 Processes That Cause Degradation of the Cellulosic Insulation 453.1.2.2 Degradation Products from Cellulosic Insulation 463.1.3 Effect of Paper Deterioration on Transformer Performance 473.2 Procedure of Accelerated Thermal Aging 483.2.1 IEEE Std. C57. 100 483.2.2 Iec 60216 493.2.3 Accelerated Thermal Aging Conditions 503.2.3.1 Temperature 503.2.3.2 Atmosphere 503.2.3.3 Moisture 503.2.3.4 Other Materials 513.2.3.5 Electrical Stress 523.3 Assessment of Liquid Degradation 523.3.1 Physicochemical Properties 523.3.2 Dielectric Properties 533.4 Assessment of Paper Degradation 553.4.1 Chemical Properties 553.4.1.1 Moisture Content 553.4.1.2 Degree of Polymerization 553.4.1.3 Fourier Transform Infrared Spectroscopy and X- ray Spectroscopy 583.4.1.4 Furanic Compounds, Methanol Content, and Gases Production 583.4.2 Mechanical Properties 593.4.2.1 Tensile Strength 593.4.2.2 Relationship Between Degree of Polymerization (DP) and Mechanical Properties 623.4.2.3 Scanning Electron Microscope (SEM) 623.4.2.4 Refractive Index of Cellulose Fibers (RI) 633.4.3 Dielectric Properties 643.4.3.1 Breakdown Voltage 643.4.3.2 Partial Discharges 653.4.3.3 Dielectric Loss Factor 653.4.3.4 Dielectric Permittivity 653.4.3.5 Conductivity 663.4.3.6 Polarization and Depolarization Currents 663.5 Remaining Life of Transformer Insulation 663.5.1 Ieee C57. 91 673.5.2 Iec 60076- 7 693.5.3 Kinetic Approach to Modeling 713.5.3.1 Polymerization Degree 713.5.3.2 Tensile Strength 733.6 Conclusions 76References 784 Degradation Assessment of Ester Liquids 85A.J. Amalanathan, R. Sarathi, N. Harid, and H. Griffiths4.1 Introduction 854.1.1 Types of Ester Fluids 854.1.2 Properties of Ester Fluids 864.1.2.1 Breakdown Voltage 874.1.2.2 Moisture Content 894.1.2.3 Flash Point and Fire Point 904.1.2.4 Viscosity 904.1.2.5 Oxidation Stability 914.1.2.6 Dielectric Constant and Dissipation Factor 914.1.2.7 Biodegradability 924.1.3 Fluid Maintenance and Storage Issues 924.2 Procedure of Accelerated Thermal Aging 934.2.1 Astm D1934- 95 934.2.2 Iec 62332- 2 934.2.3 Temperature 944.2.4 Atmosphere 944.2.5 Moisture 944.3 Assessment of Liquid Degradation 954.3.1 Partial Discharge Inception Voltage 954.3.1.1 Measurement of PDIV Under AC and DC Voltage 964.3.1.2 Measurement of PDIV Under Harmonic Voltage 974.3.2 Flow Electrification 984.3.2.1 Flow Electrification Measurement Methods 984.3.3 Spectroscopic Studies 1024.3.3.1 UV- Visible Spectroscopy 1034.3.3.2 Fluorescence Spectroscopy 1044.3.4 Dielectric Response Spectroscopy 1074.3.5 Physico- Chemical Studies 1084.3.5.1 Interfacial Tension 1084.3.5.2 Turbidity 1094.3.5.3 Viscosity 1094.3.5.4 Organic Composition of Oil Using GC- MS 1104.4 Assessment of Paper Degradation 1104.4.1 Surface Discharge Analysis 1114.4.2 Surface Potential Measurement 1124.4.3 Impedance Spectroscopy 1134.4.4 Py- GC/MS 1164.4.5 Laser- Induced Breakdown Spectroscopy 1174.5 Conclusions and Future Scope 120References 1205 End Life Behavior of Ester Liquids in High- Voltage Transformers 127U. Mohan Rao, I. Fofana, L. Loiselle, and T. Jayasree5.1 Introduction 1275.2 Evolution of Colloidal and Soluble Decay Particles 1285.2.1 Perspective of Decay Particles 1285.2.2 Size and Influence of Decay Particles 1295.3 Colloidal Particles – Centrifugal Treatment (ASTM D1698) 1305.3.1 UV Spectroscopy 1325.3.2 Turbidity 1335.3.3 Particle Counter 1355.4 Soluble Particles – Fuller’s Earth Filtration (ASTM D7150) 1375.4.1 UV Spectroscopy 1375.4.2 Turbidity 1385.4.3 Particle Counter 1395.5 Feasibility of Fuller’s Earth Filtration for Ester Liquids 1405.5.1 On Ratio of Fuller’s Earth to Liquid 1415.5.2 On Treatment Temperature 1425.6 Conclusions and Future Scope 144References 1456 Prebreakdown and Breakdown Phenomena in Ester Dielectric Liquids 147Pawel Rozga, T. Jayasree, U. Mohan Rao, I. Fofana, and P. Picher6.1 Introduction 1476.2 Research Methods in Assessment of Prebreakdown Phenomena in Ester Liquids 1486.2.1 Standard- Based Approach 1496.2.2 Experimental Approach 1496.3 Initiation of Streamers in Dielectric Liquids 1506.3.1 Influence of Tip Radius on Streamer Initiation 1516.3.2 Streamer Initiation Mechanisms 1536.3.3 Research Progress on Streamer Initiation in Esters vs. Mineral Oil 1556.4 Streamer Propagation 1566.4.1 Overview of Propagation Modes 1566.4.2 Streamer Development Theories 1626.4.3 Streamer Propagation and Breakdown in Esters vs. Mineral Oils 1676.4.4 Influence of Nanoparticles on Prebreakdown Phenomena in Ester Liquids 1726.5 Influence of Temperature on Prebreakdown Phenomena in Natural Ester Liquids 1736.6 Influence of Thermal Aging on Prebreakdown Phenomena in Synthetic Ester Liquids 1766.7 Conclusions and Future Scope 177References 1787 Miscibility and Engineering Application of a Novel Mixed Fluid 185Jian Hao, Ruijin Liao, Lijun Yang, Dawei Feng, Wenyu Ye, Chenyu Gao, and Xin Chen7.1 Introduction 1857.2 Need and Research Progress of Mixed Insulating Liquids 1867.3 Preparation Method for the New Mixed Insulating Oil 1877.3.1 Selection of the Base Oil 1877.3.2 Determination of the Proportion 1887.3.3 Improvement of Oxidation Stability 1897.3.4 Stability Overall Performance 1897.3.5 Performance of Novel Three- Element Mixed Insulating Oil 1917.4 Thermal Aging Characteristics of the New Mixed Insulation Oil–Paper Insulation and Its Delaying Thermal Aging Mechanism 1937.4.1 Introduction 1937.4.2 DP Values of Cellulose Paper 1957.4.3 Mechanism of Delaying Thermal Aging 1997.5 Mechanism of Property Enhancement of the New Mixed Insulation Oil on Power Frequency Breakdown of Oil–Paper Insulation 2037.5.1 Introduction 2037.5.2 Oils Breakdown Voltage with Different Moisture Contents 2047.5.3 Oils Breakdown Voltage with Different Temperatures 2057.5.4 Oil Breakdown Voltage Under Combined Effects of Moisture and Temperature 2067.5.5 Comparison of AC Breakdown Characteristics of Composite Insulation with Different Temperatures and Moisture Contents 2087.5.6 Comparison of AC Breakdown Characteristics of Composite Insulation with Oil Gap 2127.6 Enhancing Effect and Mechanism of the New Mixed Insulation Oil on Flashover Voltage of Oil–Paper Insulation 2147.6.1 Introduction 2147.6.2 Surface Flashover Voltage of Oil- Cellulose Insulation Pressboard 2157.6.3 Surface Flashover Difference Analysis 2187.7 Application of the New Mixed Insulation Oil: Service Experiences 2217.7.1 Introduction 2217.7.2 Using the New Three- Element Mixed Insulation Oil in10 kV Transformer 2227.7.3 Overheating and Discharge Fault Identification for Novel Three- Element Mixed Oil- Paper Insulation System 2227.7.4 Fault- Type Identification Model Based on Hydrogen, Ethane, and Acetylene 2317.8 Conclusions and Future Scope 233References 2368 Natural Ester Nanosfluids as Alternate Insulating Oils for Transformers 241Joyce Jacob, Preetha Prabhu, and Sindhu Thiruthi Krishnan8.1 Introduction 2418.1.1 Importance of Nanofluids 2418.1.2 Improvement of Natural Esters 2428.1.2.1 Additives for Chemical Structure Modification 2428.1.2.2 Addition of Nanoparticles 2448.1.3 Commonly Used Nanoparticles 2448.2 Preparation of Natural Ester Nanofluids and Stability Analysis 2458.2.1 Preparation of Natural Ester Nanofluids 2458.2.1.1 Different Methods of Nanofluid Preparation 2458.2.2 Stability of Natural Ester Nanofluids 2488.2.2.1 Stability of Nanofluids 2488.2.2.2 Methods of Stability Improvement of Natural Ester Nanofluids 2508.2.2.3 Methods of Stability Analysis of Natural Ester Nanofluids 2528.3 Properties of Natural Esters and Natural Ester Nanofluids 2548.3.1 Physical Properties 2548.3.2 Electrical Properties 2548.3.2.1 Permittivity of Nanofluids 2548.3.2.2 Partial Discharge and Breakdown Voltage in Nanofluids 2588.3.3 Thermal Properties 2618.3.4 Aging Study of Natural Ester Nanofluids 2638.3.5 Feasibility of Natural Ester Nanofluids as an Alternate Insulating Oil for Transformers 2668.4 Conclusion 2678.4.1 Stability Enhancement of Natural Ester Nanofluids 2678.4.2 Simulation Model for Nanofluids 2688.4.3 Design of Transformers Using Natural Ester Nanofluids 2688.4.4 Mixed Fluids and Multiparticle Nanofluids 268References 2689 Dielectric Properties of Silica- Based Synthetic Ester Nanofluid 273G. D. P. Mahidhar, R. Sarathi, Nathaniel Taylor, and Hans Edin9.1 Introduction 2739.1.1 Need for Nanofluids 2749.1.2 Methods of Property Enhancement of Nanofluids 2749.2 Nanofluid Preparation and Characterization 2779.2.1 Nanoparticle Characterization 2779.2.2 Nanofluid Preparation 2789.2.3 Nanofluid Stability 2799.2.3.1 Particle Size Analysis 2799.2.3.2 Zeta Potential Analysis 2819.2.3.3 Viscosity Measurement 2819.3 Frequency Domain Dielectric Response 2829.3.1 Experimental Setup 2829.3.2 Dielectric Constant 2839.3.3 Dissipation Factor 2839.4 Time Domain Dielectric Response 2859.4.1 Experimental Setup 2859.4.2 Ion Mobility 2869.4.3 Conductivity and Other Dielectric Properties 2899.5 Conduction at High Electric Field 2909.5.1 Experimental Setup 2909.5.2 I–U Characteristics 2919.6 Corona Inception Voltage 2939.6.1 Experimental Setup 2939.6.2 civ Results and Discussion 2949.6.3 Incipient Discharge Activity 2969.6.3.1 Corona Discharge Activity Under Harmonic AC Voltages 2969.6.3.2 UHF Signal Energy Analysis 2979.7 Conclusions and Future Scope 298References 30010 Behavior of Ester Liquids Under Various Operating Fault Conditions 305U. Mohan Rao, I. Fofana, and L. Loiselle10.1 Introduction 30510.2 Dissolved Gas Analysis and Transformer Faults 30610.2.1 Duval’s Triangle 30710.2.2 Duval’s Pentagon 30810.2.3 Research Progress on Various Faulty Conditions 30810.3 Simulation of Various Faults in Laboratory Environment 31010.3.1 Low- Energy Discharges (Surface Discharges) 31010.3.2 Thermal Faults (Hotspot) 31010.3.3 High- Energy Discharges (Arcing) 31110.4 Influence of Different Faults on the State of Liquid and Gassing Tendency 31110.4.1 Effect on Gassing Tendency 31410.4.2 Effect on Degradation 31510.5 Conclusions and Future Scope 318References 31911 In- Service Performance of Natural Esters 321D. Martin and L. McPherson11.1 Introduction 32111.2 Reasons Why These Utilities Chose a Natural Ester 32211.3 Transformers Under Study 32211.4 Summary of Research Applied to Manage These Transformers 32311.5 Fluid Temperature at Rated Load 32411.6 Breakdown Voltage and Water Content 32511.7 Investigations into Oxidation and Handling Fluid- Impregnated Paper 32611.8 Study on Installation and Early Operation of a Power Transformer Filled with Natural Ester 33011.9 Fleet Measurements 33311.9.1 Dielectric Dissipation Factor, Interfacial Tension, and Acid Number 33411.9.2 Water Content of Oil 33411.9.3 Breakdown Voltage of Oil 33611.9.4 Dissolved Gas Analysis 33711.9.5 Electrical Testing of Transformers 33811.10 Summary 341References 342Index 345