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Experimental and Mathematical Modeling Studies on Current Distribution in High Temperature Superconducting DC Cables Venkata Pothavajhala

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Experimental and Mathematical Modeling Studies on Current Distribution in High Temperature Superconducting DC Cables Venkata Pothavajhala Florida State University Libraries Electronic Theses, Treatises and Dissertations The Graduate School 2014 Experimental and Mathematical Modeling Studies on Current Distribution in High Temperature Superconducting DC Cables Venkata Pothavajhala Follow this and additional works at the FSU Digital Library. For more information, please contact [email protected] FLORIDA STATE UNIVERSITY COLLEGE OF ENGINEERING EXPERIMENTAL AND MATHEMATICAL MODELING STUDIES ON CURRENT DISTRIBUTION IN HIGH TEMPERATURE SUPERCONDUCTING DC CABLES By VENKATA POTHAVAJHALA A Thesis submitted to the Department of Electrical and Computer Engineering in partial fulfillment of the requirements for the degree of Master of Science Degree Awarded: Summer Semester, 2014 Venkata Pothavajhala defended this thesis on June 24, 2014. The members of the supervisory committee were: Chris Edrington Professor Directing Thesis Lukas Graber Committee Member Petru Andrei Committee Member The Graduate School has verified and approved the above-named committee members, and certifies that the thesis has been approved in accordance with university requirements. ii I dedicate this work to my parents and to my research supervisor iii ACKNOWLEDGMENTS I would like thank Professor Chris S. Edrington for being an excellent academic advisor and guiding me through the MS program and helping me choose my course work and planning my research. I would like to express my deepest appreciation and sincere gratitude to my research supervisor Dr. Sastry Pamidi for providing me the opportunity to work under his guidance and for his continuous support throughout my research. It is a pleasure working under such a great scientist. I’m thankful to him for spending the time for our weekly discussions though he is very busy with other projects, proposals and meetings. He is always ready to help students and colleagues professionally and also personally in all possible ways. I am greatly thankful to Dr. Lukas Graber who provided much support for my research. He also gave me many tips and suggestions on how to work and present in a professional way. I thank him for spending time to meet almost every week to discuss my research. Dr. Chul H. Kim is another person who continuously supported me right from the beginning of my work at CAPS. I express my sincere appreciation to him for training me in the laboratory on the experimental techniques. I understand that it is not easy to teach every time a new student joins the group to make him/her understand how things work. Dr. Kim was very patient in doing so. He also spent much time every week in helping me to present my work in a useful and understandable way. It would not be possible for me to successfully publish in the IEEE Transactions on Applied Superconductivity without the strong help and guidance from all the above mentioned researchers. I also strongly believe that the applied superconductivity and cryogenics group at CAPS is a great place to do research and grow professionally and personally. I am thankful for the Office of Naval Research and Center for Advanced Power Systems for providing me the funding and state of the art research facilities and wonderful opportunities to learn about latest research in electrical power technologies. I wholeheartedly thank my parents for providing me the opportunity to pursue Masters. Especially, I’m grateful to my mother who provided moral support and motivation required for my study and research work. It’s her constant encouragement that helped me in moving towards my goal. iv TABLE OF CONTENTS LIST OF TABLES ........................................................................................................................ vii LIST OF FIGURES ..................................................................................................................... viii ABSTRACT .................................................................................................................................... x 1. INTRODUCTION ...................................................................................................................... 1 1.1 Discovery of Superconductivity ........................................................................................... 1 1.1.1 The Meissner effect........................................................................................................ 2 1.1.2 Electrodynamics and thermodynamics of superconductivity ........................................ 3 1.1.3 Quantum mechanics of superconductivity ..................................................................... 4 1.2 Types of Superconductors ..................................................................................................... 6 1.2.1 Low temperature superconductors ................................................................................. 6 1.2.2 High temperature superconductors ................................................................................ 6 1.2.3 First generation (1G) superconductors........................................................................... 8 1.2.4 Second generation (2G) superconductors ...................................................................... 8 2. APPLICATIONS ...................................................................................................................... 10 2.1 Digital Electronics .............................................................................................................. 10 2.2 Medical Applications .......................................................................................................... 10 2.3 Electric Power ..................................................................................................................... 11 2.3.1 Machines ...................................................................................................................... 11 2.3.2 Power transformers ...................................................................................................... 11 2.3.3 Fault current limiters .................................................................................................... 12 2.3.4 Magnetic energy storage .............................................................................................. 12 2.3.5 Magnetic levitation trains ............................................................................................ 12 2.4 Particle Physics ................................................................................................................... 13 2.5 Fusion Technology.............................................................................................................. 13 2.6 Space Applications.............................................................................................................. 14 3. SUPERCONDUCTING POWER CABLES ............................................................................ 15 3.1 Overview ............................................................................................................................. 15 3.2 Research Objective ............................................................................................................. 18 4. RESULTS OF CABLE MEASUREMENTS ........................................................................... 21 4.1 Measurement of Critical Current and Index Value of Tapes in 2G HTS Cable ................. 21 5. EXPERIMENTS ON DISTRIBUTION OF CURRENT IN 2G HTS CABLES ..................... 23 v 5.1 Experimental Procedure ...................................................................................................... 23 5.1.1 Measurement of critical current ................................................................................... 24 5.1.2 Measurement of index (n) value .................................................................................. 24 5.1.3 Measurement of contact resistances............................................................................. 24 5.1.4 Measurement of current through individual tapes ....................................................... 25 5.2 Mathematical Model ........................................................................................................... 25 5.3 Simulations ......................................................................................................................... 27 5.3.1 Effects of variation of contact resistance ..................................................................... 27 5.3.2 Effects of variation of critical current .......................................................................... 28 5.3.3 Effects of variation of index value ............................................................................... 29 5.4 Analysis Using Monte Carlo Simulations........................................................................... 30 5.4.1 Introduction to Monte Carlo ........................................................................................ 30 5.4.2 Monte Carlo simulations .............................................................................................. 31 5.5 Discussion of Results .......................................................................................................... 33 6. EFFECT OF LONGITUDINAL VARIATIONS IN CHARACTERISTICS OF INDIVUDUAL TAPES ON THE PERFORMANCE OF SUPERCONDUCTING CABLE ...... 34 6.1 Longitudinal Variation in Critical Current ......................................................................... 35 6.2 Longitudinal Variation in Index Value
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