Modelling Thermal Rating of Arbitrary Overhead Line Systems

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Modelling Thermal Rating of Arbitrary Overhead Line Systems

K. Kopsidas

PhD

2009

The University of Manchester

233

List of Figures 5List of Tables 8Abbreviations 9List of Terms 11Abstract 15Declaration 16Copyright 16Acknowledgements 17Dedication 18CHAPTER 1 . Introduction 191.1. Research Background 201.2. Aims and Objectives 221.3. Overview 23CHAPTER 2 . Techniques for Uprating Existing Lines 272.1. Constraints of Power Transfer Through an OHL 282.2. Categorization of Uprating Methods 312.2.1. Increasing Thermal Limit 312.2.2. Increasing Dynamic Limit 332.3. Flexible AC Transmission (FACT) Devices 342.3.1. Phase Shifting Transformers 342.3.2. Shunt Mechanical Switched Capacitors 352.3.3. Series Mechanical Switched Capacitors 362.3.4. Static Var Compensators (SVCs) 372.3.5. Synchronous Static Compensators (STATCOMs) 372.4. Re-tensioning and Re-conductoring 382.4.1. Re-tensioning an OHL 392.4.2. Re-conductoring an OHL 402.5. High-Temperature Low-Sag (HTLS) Conductor Types 412.5.1. Gap Type Thermal Resistant Aluminium Alloy, Steel Reinforced (GTACSR) 412.5.2. Zirconium Thermally Resistant Aluminium Alloy Conductor Invar Reinforced (ZTACIR) 422.5.3. Aluminium Conductor Steel Supported (ACSS) 422.5.4. Aluminium Conductor Composite Reinforced (ACCR) 432.5.5. Aluminium Conductor Composite Core (ACCC) 442.5.6. Comparison of the Properties of the Different Conductor Types 442.6. Conclusion 48CHAPTER 3 . A Holistic Methodology for Rating an OHL 493.1. Parameters Influencing Sag-Tension -Temperature Calculations 493.2. Conductor Sag Calculations 513.2.1. Conductor Sag Equation on Flat Terrain 513.2.2. Conductor sag Equation on Inclined terrain 563.3. Mechanical and Ageing Calculations 603.3.1. Conductor Ageing Effect 603.3.2. Conductor Thermal and Elastic Elongation Effects 663.4. Electrical Computations 703.4.1. Calculation of ACSR DC Resistance at 20 °C 713.4.2. Calculation of ACSR AC Resistance at Any Temperature Including the Skin Effect (Frequency) 743.4.3. Calculation of the Core Magnetization Coefficient of ACSR 813.4.4. Calculation of the AC Resistance of ACSR Considering All the Parameters 843.5. Design Loading Conditions of an OHL System 863.5.1. Conditions Defining Maximum Mechanical Loading 873.5.2. Maximum Conductor Tension Loading Calculation 893.5.3. Conditions and Calculation of OHL Electrical Loading 923.6. Software Implementation 943.7. Conclusion 94CHAPTER 4 . Analysis of Electrical & Mechanical Properties of Bare Conductors on a 33 kV Wood Pole System 984.1. 33 kV Wood Pole Single Circuit System 984.2. Maximum Mechanical Loading Analysis 1004.3. Maximum Electrical Loading Analysis 1034.4. Discussion 1074.5. Conclusion 112CHAPTER 5 . Standard AAAC and ACSR Conductors on a 33 kV OHL Structure 1145.1. Comparison of Maximum Mechanical Loading Performance 1155.2. Comparison of Maximum Electrical Loading Performance 1175.2.1. Sag at Maximum Electrical Loading 1185.2.2. Ampacity and Losses at Maximum Electrical Loading 1195.3. Use of Vibration dampers on the 33 kV OHL system 1215.4. Conductor Operating Temperature (TOP) 1235.5. Ambient Air Temperature (TA) 1285.6. Conductor Creep-Strain 1315.7. Discussion 1365.8. Conclusion 139CHAPTER 6 . HTLS Conductors on a 33 kV OHL Structure 1416.1. Description of the ACCR and ACCC/TW Conductors 1416.2. ACCR and ACCC/TW Performance on the 33 kV OHL Structure 1436.2.1. Mechanical Performance on the 33 kV OHL Structure 1436.2.2. Electrical Performance on the 33 kV OHL Structure 1486.3. Conductor Operating Temperature Effect on ACCR & ACCC/TW 1506.4. Discussion 1536.5. Conclusion 157CHAPTER 7 . Analysis of Common Types and Advanced HTLS Conductors on a Lattice Tower OHL System 1597.1. 275 kV Lattice Tower OHL System 1597.2. Electrical and Mechanical Loading Analysis of AAAC – Sag Zones 1607.2.1. Effect of Structure Strength on System Performance 1607.2.2. Span Length Influence on Lattice Tower Systems 1637.2.3. Performance Comparison Between Bundles on L3 Tower 1657.3. Performance Comparison of Different Conductor Technologies 1687.3.1. Single Bundle Conductor Mechanical & Electrical Performance 1687.3.2. Twin Bundle Conductor Mechanical & Electrical Performance 1747.3.3. Operating Temperature Effect on System’s Holistic Performance 1777.4. Discussion 1807.5. Conclusions 183CHAPTER 8 . Implementation of the Methodology on a Real OHL System 1858.1. Real OHL System Study 1858.2. Conclusion 190CHAPTER 9 . Main Contribution 1929.1. Implementation of the Computational Methodology 1929.2. Conclusions 1949.3. Further Work 196References 198Appendix A : Conductor Types – Basic Properties 205Appendix B : L2 Type Lattice Tower and Surveyed OHL Data 206Appendix C : Publications 211

The aim of this project is to identify methods for improving the power transfer capacity of existing overhead power lines (OHL) with changes that require small modifications of the structure. These methods usually involve re-conductoring of the line with larger ‘traditional’, all aluminium alloy conductors (AAAC) or aluminium conductor steel reinforced (ACSR) or more technologically advanced high temperature low sag (HTLS) conductors. These options and their effects are investigated in this thesis by considering the overall OHL system and not only the conductor. Towards this end a holistic computational methodology has been developed to allow sag-ampacity-tension calculations considering electro-mechanical properties of arbitrary OHL systems. This methodology can be used for any aerial power line design to calculate the maximum sag, ampacity and losses developed under specified weather and operating conditions on flat and inclined terrain with common or novel conductors. Surveyed data of three OHL sections were used to verify the accuracy of the methodology. The results showed that the electrical calculations were in all cases very close to the measured values, and also that the sag prediction was correct and more accurate than the existing method of fixed temperature shift on two of the sections.Results are subsequently presented as illustrative applications of this methodology to show potential benefits from such a holistic perspective on the system. Firstly, the mechanical performance of conductors on a 33 kV wood pole OHL system is considered as a continuum and is divided into three main zones of sag which describe the system’s performance for different conductor sizes. Due to the complexity of OHL systems it was considered important to firstly examine the performance of the traditional AAAC and ACSR conductors on the structure and identify the influence of key parameters of the system (OHL strength, conductor strength, conductor weight etc.) on electrical and mechanical performance. This led to the conclusion that AAAC perform better on this particular system than the ACSR conductors due to their lighter design. Another comparison involved HTLS conductors which are known for their high improved performance at elevated operating temperatures (above 90 °C). Results indicated that the aluminium conductor composite core conductors (ACCC/TWs), which have also improved performance at normal operating temperatures, can allow voltage uprating of an existing 33 kV system up to 66 kV. Finally, performance analysis was performed for a 275 kV lattice tower OHL system, and it was found that the composite HTLS conductor types studied can double the ampacity of the lattice tower OHL. It was also found that conductor bundle configuration has better performance due to the reduction in weight and increase in strength. This allows larger conductor sizes on the same OHL structure, a conclusion which also identifies the importance of OHL structure strength on its overall performance.

• Kopsidas, Konstantinos

• Faculty of Engineering and Physical Sciences
• School of Electrical and Electronic Engineering

uk-ac-man-scw:103843

Kopsidas, Konstantinos

6th January, 2011, 23:40:14

Kopsidas, Konstantinos

29th March, 2011, 20:06:14