Electromagnetic Transient Analysis and Novel Protective Relaying Techniques for Power Transformers

Xiangning Lin, Professor, College of Electrical and Electronic Engineering, Huazhong University of Science and Technology, China.Prof. Lin was the first to discover the ultra-saturation phenomenon of power transformer and he designed operating characteristics analysis planes to make clear the advantages and disadvantages of existing differential protection of power transformer. He invented a variety of novel protection algorithms for the main protection of the power transformer. A series of papers were published in journals including IEEE Transactions on Power Systems and IEEE Transactions on Power Delivery. The work has been widely acknowledged and cited by international peers. He also pioneers the introduction of modern signal processing techniques to design the protection criteria for power transformer. He was the winner of the 2nd Class National Natural Science Award in 2009. He has published nearly 200 papers and books (in Chinese), he also owns over 15 patents. Jing Ma, Associate Professor, School of Electrical and Electronic Engineering, North China Electric Power University, Beijing, China.Prof. Ma was the first to apply the two-terminal network algorithm to the areas of power system protection. The work has been widely acknowledged and cited by international peers. He also proposed an approach based on grille fractal to solve the TA saturation problem, and the related paper has been published in the IEEE Transactions on Power Delivery. The research results were used in many practical engineering projects.Dr. Qing Tian, Senior Engineer with the Maintenance and Test Center of EHV Transmission Co. Ltd, Southern Power Grid, Guangzhou, China.Dr. Hanli Weng, Senior Engineer with Three-Gorge Hydropower Plant, China Yangtze Power Co., Ltd.Both have been working in this area since 1995. Their main research fields include power system operation analysis and control, voltage and reactive power optimization, power system reliability and risk assessment and power system energy saving assessment and planning.

• About the Authors ixPreface xi1 Principles of Transformer Differential Protection and Existing Problem Analysis 11.1 Introduction 11.2 Fundamentals of Transformer Differential Protection 21.2.1 Transformer Faults 21.2.2 Differential Protection of Transformers 31.2.3 The Unbalanced Current and Measures to Eliminate Its Effect 51.3 Some Problems with Power Transformer Main Protection 71.3.1 Other Types of Power Transformer Differential Protections 71.3.2 Research on Novel Protection Principles 91.4 Analysis of Electromagnetic Transients and Adaptability of Second Harmonic Restraint Based Differential Protection of a UHV Power Transformer 171.4.1 Modelling of the UHV Power Transformer 181.4.2 Simulation and Analysis 201.5 Study on Comparisons among Some Waveform Symmetry Principle Based Transformer Differential Protection 271.5.1 The Comparison and Analysis of Several Kinds of Symmetrical Waveform Theories 271.5.2 The Theory of Waveform Symmetry of Derivatives of Current and Its Analysis 281.5.3 Principle and Analysis of the Waveform Correlation Method 321.5.4 Analysis of Reliability and Sensitivity of Several Criteria 331.6 Summary 36References 362 Malfunction Mechanism Analysis due to Nonlinearity of Transformer Core 392.1 Introduction 392.2 The Ultra-Saturation Phenomenon of Loaded Transformer Energizing and its Impacts on Differential Protection 432.2.1 Loaded Transformer Energizing Model Based on Second Order Equivalent Circuit 432.2.2 Preliminary Simulation Studies 482.3 Studies on the Unusual Mal-Operation of Transformer Differential Protection during the Nonlinear Load Switch-In 572.3.1 Simulation Model of the Nonlinear Load Switch-In 572.3.2 Simulation Results and Analysis of Mal-Operation Mechanism of Differential Protection 622.4 Analysis of a Sort of Unusual Mal-operation of Transformer Differential Protection due to Removal of External Fault 702.4.1 Modelling of the External Fault Inception and Removal and Current Transformer 702.4.2 Analysis of Low Current Mal-operation of Differential Protection 722.5 Analysis and Countermeasure of Abnormal Operation Behaviours of the Differential Protection of the Converter Transformer 802.5.1 Recurrence and Analysis of the Reported Abnormal Operation of the Differential Protection of the Converter Transformer 802.5.2 Time-Difference Criterion to Discriminate between Faults and Magnetizing Inrushes of the Converter Transformer 862.6 Summary 95References 953 Novel Analysis Tools on Operating Characteristics of Transformer Differential Protection 973.1 Introduction 973.2 Studies on the Operation Behaviour of Differential Protection during a Loaded Transformer Energizing 993.2.1 Simulation Models of Loaded Transformer Switch-On and CT 993.2.2 Analysis of the Mal-operation Mechanism of Differential Protection 1023.3 Comparative Investigation on Current Differential Criteria between One Using Phase Current and One Using Phase–Phase Current Difference for the Transformer using Y-Delta Connection 1093.3.1 Analyses of Applying the Phase Current Differential to the Power Transformer with Y/Δ Connection and its Existing Bases 1093.3.2 Rationality Analyses of Applying the Phase Current Differential Criterion to the Power Transformer with Y/Δ Connection 1133.4 Comparative Analysis on Current Percentage Differential Protections Using a Novel Reliability Evaluation Criterion 1173.4.1 Introduction to CPD and NPD 1173.4.2 Performance Comparison between CPD and NPD in the Case of CT Saturation 1183.4.3 Performance Comparison between CPD and NPD in the Case of Internal Fault 1213.5 Comparative Studies on Percentage Differential Criteria Using Phase Current and Superimposed Phase Current 1233.5.1 The Dynamic Locus of p - 1p +1 in the Case of CT Saturation 1233.5.2 Sensitivity Comparison between the Phase Current Based and the Superimposed Current Based Differential Criteria 1263.5.3 Security Comparison between the Phase Current Based and the Superimposed Current Based Differential Criteria 1283.5.4 Simulation Analyses 1303.6 A Novel Analysis Methodology of Differential Protection Operation Behaviour 1323.6.1 The Relationship between Transforming Rate and the Angular Change Rate under CT Saturation 1323.6.2 Principles of Novel Percentage Restraint Criteria 1333.6.3 Analysis of Novel Percentage Differential Criteria 1423.7 Summary 151References 1514 Novel Magnetizing Inrush Identification Schemes 1534.1 Introduction 1534.2 Studies for Identification of the Inrush Based on Improved Correlation Algorithm 1554.2.1 Basic Principle of Waveform Correlation Scheme 1554.2.2 Design and Test of the Improved Waveform Correlation Principle 1594.3 A Novel Method for Discrimination of Internal Faults and Inrush Currents by Using Waveform Singularity Factor 1634.3.1 Waveform Singularity Factor Based Algorithm 1634.3.2 Testing Results and Analysis 1644.4 A New Principle of Discrimination between Inrush Current and Internal Fault Current of Transformer Based on Self-Correlation Function 1694.4.1 Basic Principle of Correlation Function Applied to Random Single Analysis 1694.4.2 Theory and Analysis of Waveform Similarity Based on Self-Correlation Function 1704.4.3 EPDL Testing Results and Analysis 1734.5 Identifying Inrush Current Using Sinusoidal Proximity Factor 1744.5.1 Sinusoidal Proximity Factor Based Algorithm 1744.5.2 Testing Results and Analysis 1764.6 A Wavelet Transform Based Scheme for Power Transformer Inrush Identification 1814.6.1 Principle of Wavelet Transform 1814.6.2 Inrush Identification with WPT 1854.6.3 Results and Analysis 1854.7 A Novel Adaptive Scheme of Discrimination between Internal Faults and Inrush Currents of Transformer Using Mathematical Morphology 1904.7.1 Mathematical Morphology 1904.7.2 Principle and Scheme Design 1934.7.3 Testing Results and Analysis 1944.8 Identifying Transformer Inrush Current Based on Normalized Grille Curve 2024.8.1 Normalized Grille Curve 2024.8.2 Experimental System 2054.8.3 Testing Results and Analysis 2074.9 A Novel Algorithm for Discrimination between Inrush Currents and Internal Faults Based on Equivalent Instantaneous Leakage Inductance 2114.9.1 Basic Principle 2114.9.2 EILI-Based Criterion 2174.9.3 Experimental Results and Analysis 2184.10 A Two-Terminal Network-Based Method for Discrimination between Internal Faults and Inrush Currents 2224.10.1 Basic Principle 2224.10.2 Experimental System 2304.10.3 Testing Results and Analysis 2304.11 Summary 234References 2345 Comprehensive Countermeasures for Improving the Performance of Transformer Differential Protection 2375.1 Introduction 2375.2 A Method to Eliminate the Magnetizing Inrush Current of Energized Transformers 2425.2.1 Principles and Modelling of the Inrush Suppressor and Parameter Design 2425.2.2 Simulation Validation and Results Analysis 2495.3 Identification of the Cross-Country Fault of a Power Transformer for Fast Unblocking of Differential Protection 2555.3.1 Criterion for Identifying Cross-Country Faults Using the Variation of the Saturated Secondary Current with Respect to the Differential Current 2555.3.2 Simulation Analyses and Test Verification 2575.4 Adaptive Scheme in the Transformer Main Protection 2685.4.1 The Fundamental of the Time Difference Based Method to Discriminate between the Fault Current and the Inrush of the Transformer 2685.4.2 Preset Filter 2695.4.3 Comprehensive Protection Scheme 2715.4.4 Simulation Tests and Analysis 2745.5 A Series Multiresolution Morphological Gradient Based Criterion to Identify CT Saturation 2945.5.1 Time Difference Extraction Criterion Using Mathematical Morphology 2945.5.2 Simulation Study and Results Analysis 2975.5.3 Performance Verification with On-site Data 3025.6 A New Adaptive Method to Identify CT Saturation Using a Grille Fractal 3045.6.1 Analysis of the Behaviour of CT Transient Saturation 3045.6.2 The Basic Principle and Algorithm of Grille Fractal 3085.6.3 Self-Adaptive Generalized Morphological Filter 3125.6.4 The Design of Protection Program and the Verification of Results 3135.7 Summary 317References 317Index 319