2248 IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 17, NO. 2, JUNE 2007 Conduction-Cooled Brass Current Leads for a Resistive Superconducting Fault Current Limiter (SFCL) System H. G. Lee, H. M. Kim, B. W. Lee, I. S. Oh, H.-R. Kim, O. B. Hyun, J. Sim, H. M. Chang, J. Bascunan, and Y. Iwasa Abstract—This paper presents the design and performance re- sults of a pair of conduction-cooled brass current leads for a resis- tive superconducting fault current limiter (SFCL) system. The 24 kV class SFCL, which has been recently developed by the KEPRI- LSIS collaboration group in Korea, requires three pairs of con- duction-cooled brass current leads operated continuously at 630 A. When the SFCL system is in the fault-mode, the current leads have experienced a 60-Hz fault current of 10 kA at 24 kV for 3–5 cycles. In this paper, we present the performance results of the conduction-cooled brass (commercial brass, 10% Zn) leads having a rated current of 667 A operated in a bath of liquid nitrogen. Index Terms—Brass current lead, superconducting fault current limiter (SFCL). I. INTRODUCTION T HE development of thermally-stable current leads for a su- perconducting fault current limiter (SFCL) having a min- imum heat input at the cold-end is very important because SFCL has frequently experienced a fault current, that is 20 times its rated current, when the SFCL system is in the fault-mode. The 24 kV/630 A-SFCL is being developed by collaboration between the Korea Electric Power Research Institute (KEPRI) and LS Industrial Systems (LSIS), which is supported by a grant from the Center for Applied Superconductivity Technology of the 21st Century Frontier R&D Program funded by the Ministry of Science and Technology, Korea. This resistive SFCL system requires three pairs of conduction-cooled current leads. Of the two main types of materials to be used for conduc- tion-cooled current lead commonly, copper and brass, the brass Manuscript received August 25, 2006. This work was supported in part by a Korea University Grant and a grant from the Center for Applied Supercon- ductivity Technology of the 21st Century Frontier R&D Program funded by the Ministry of Science and Technology, Republic of Korea. H. G. Lee and J. Sim are with the Division of Materials Science and Engi- neering, Korea University, Seoul, Korea (e-mail: haigunlee@ korea.ac.kr). H. M. Kim is with the Korea Electrotechnology Research Institute, Changwon, Korea. W. Lee and I. S. Oh are with the Electric Power Research Lab., LS Industrial Systems Co., Ltd., Cheongju, Korea. H.-R. Kim and O. B. Hyun are with the Superconductivity & Application Group, Korea Electric Power Research Institute, Daejeon, Korea. H. M. Chang is with the Department of Mechanical Engineering, Hong Ik University, Seoul, Korea. J. Bascunan and Y. Iwasa are with the MIT-FBML, Cambridge, MA USA. Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TASC.2007.898146 could potentially be more effective in SFCL systems. The brass lead heat input at the cold-end is smaller than that of the copper lead at rated current, because of smaller product of the elec- trical resistivity and thermal conductivity. Moreover, our recent analysis has demonstrated that brass leads are operated stably in over-current mode [1]. In this paper, we present the design/performance results of the conduction-cooled type current lead using the brass (com- mercial brass, 90% Cu 10% Zn), which is manufactured for use in our resistive SFCL. II. PROCEDURE FOR PAPER SUBMISSION A. Conduction-Cooled Current Leads Here we deal with the design of the conduction-cooled op- timum leads. The thermal behavior of the conduction-cooled current lead is analyzed by solving the one-dimensional steady- state power density differential equation given by [2] (1) where is the current lead’s cross sectional area, is a position along the current lead, and are, respectively, the temperature- averaged thermal conductivity and electrical resistivity, and is the rated transport current. Integrating (1) twice with respect to and dividing the resulting equation by , and with appropriate boundary conditions, and , the solution of (1) is obtained as follow: (2) The heat input at the cold-end, is given by (3) Differentiating (3) with respect to and setting it to 0 for shape factor, that minimizes and solving for , we obtain: (4) From (3) and (4), we have an expression for the optimum heat input to the cold-end at rated current of as follows: (5) 1051-8223/$25.00 © 2007 IEEE