Measurement of interstrand conductance in multistrand superconducting cables

Abstract

Multistrand 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 superconducting cables. Knowledge of interstrand conductance is essential for analysis of current distribution and redistribution processes that substantially influence the stability of multistrand superconducting cables. In this paper, an approach to measure 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. The interstrand conductance between the subcables in different cabling stages in a cable-in-conduit conductor (CICC) has been studied under different conditions (different temperatures and different cable lengths). The results are consistent, accurate, and fit the distributed parameters circuit model well. This method provides a convenient approach to evaluate electrical coupling parameters in multistrand superconducting cables under different conditions. The estimated parameters can be used to improve the accuracy of analysis of current distribution and cable stability.