Type of Document	Dissertation
Author	Lu, Bing
URN	etd-03172006-173643
Title	Electrical Parameters in Multi-Strand Superconducting Cables and their Effect on Stability
Degree	Doctor of Philosophy
Department	Mechanical Engineering, Department of
Advisory Committee	Advisor Name Title Cesar Luongo Committee Member David Cartes Committee Member Juan Ordonez Committee Member Micha Steures Committee Member Thomas Baldwin Committee Member
Keywords	Least Squares Method Superconducting Cables Interstrand Conductance
Date of Defense	2005-11-30
Availability	unrestricted
Abstract ABSTRACT Multi-strand superconducting cables are widely used in large scale applications to obtain large current carrying capacity. Stability is one of the key issues that ensure continuous and reliable operation of the superconducting cable. The stability of multi-strand superconducting cables is substantially influenced by the current distribution and redistribution among strands. The analysis of current distribution and edistribution in superconducting cables requires the knowledge of electric coupling parameters among strands. In this work, previous research on electrical coupling parameters, theoretical and experimental studies on current distribution, and the effect of current distribution on cable stability are reviewed. A new approach that estimates interstrand conductance is developed using parametric estimation method as used in control theory. First, a distributed parameter circuit model is adopted to calculate the current and voltage distribution in superconducting cables. Then, strand voltage differences at cable ends are measured by experiment. Finally, least squares method is applied to estimate the interstrand conductance which gives the minimum error of the voltage difference at cable ends between calculated and measured data. To utilize fresh experimental data and improve accuracy, a sequential least squares algorithm is developed. The interstrand conductance between the sub-cables in different cabling stages in a CICC has been studied under different conditions (different temperature and different cable length). The results are consistent, accurate (error less than 4%), and fit the distributed parameters circuit model well. Effects of mechanical load on interstrand conductance are also investigated. This method provides a new approach to evaluate electrical coupling parameters in multi-strand superconducting cables under different conditions (current density and frequency, mechanical loads, etc.). It is the first time that parametric estimation method from system identification theory is applied to study the interstrand conductance in superconducting cables. The estimation error is reduced by eliminating the need for approximations in the parameters themselves. The estimated parameters can improve the accuracy of analysis of current distribution and cable stability as well as shed new light in understanding how the n-value of a cable changes during magnet operation.
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