S. Yamada

Y. Hishinuma

National Institute for Fusion Science (NIFS-Repository)

??? ??????????????????????????????????????????????Fig. 2  Cable dram (a) and coaxial twisted MgB2 cable (b). 00.20.40.60.811.20 0.5 1 1.5 2 2.5mono-core @ 1.0 T19 filaments @ 2.0 T19 filaments @ 1.0 TI c strain / I c0Bending Strain  (%)0.50.5Fig. 1 Normalized Ic vs. bending strain for MgB2 mono- core wire and 19-filamentary wire. Table 1 Parameters of mono-core and19-filamentary wires. Items Mono core 19 filaments Diameter of wire (mm) Area of MgB2 (%) Area of Ta barrier (%) Area of Cu (%) Ic @20K, 1T  (A) Ic @20K, 2T  (A) 1.044.5727.3368.1076.811.045.0834.4757.4561.5634.31Table 2 Design parameters of 10 kA MgB2 cable. Items Target values Operation Temperature Material of the SC wire Diameter of the SC strand Operation Current of strand Number of the SC wire Diameter of SC cable and wire Twist ratio (P / dC)17 K – 24 K MgB21.3 mm (0.5 mm) 19.7 A  (~100 A/mm2)50726.5 : 1 30 (1035 mm / 34.5 mm) Conceptual design of 10 kA Class MgB2Cable for Hybrid Energy Transfer Line  Yamada, S , Hishinuma, Y.  It is important to understand the mechanical performance of the MgB2 wire. To suppress the Ic degradation for bending strain, multi-filamentary MgB2wires were investigated. The bending property of the 19 filamentary MgB2 wire was made, and it was tested in comparison with the mono-core MgB2 wire [1].  Configuration and Ic performances of both wires are summarized in Table 1. A relationship between the normalized Ic and bending strain for MgB2 mono-core wire and multi-filamentary wire is shown in Fig. 1  The bending strain � is defined as, ��� d / D x 100 (%).                     ( 1 ) Where the d is diameter of the wire, and D is diameter of the bend. The Ic degradation of both wires was observed.  However, about 50 % of Ic0 is remained in the multi-filamentary MgB2 wire, even if the bending strain exceeds 2 %.  This is that about half of the filaments of inside keep the Ic0 value, whenever the filaments of outside are damaged by the large bending stress [2]. The MgB2 cable should be robust for the repetition of the bend and stretch of following manufacture process of; the heat treatment, transfer to the reel, twist and bundle, transportation by cable drums and installation on site.  As shown in Fig. 2 (a), a diameter of the cable dram has the restriction of the surface transportation. Diameter of the dram is determined to 3 m. When the cable is wounded to the cable dram, tensile stress and compressive stress are induced to the outside and inside of the bend, as shown in Fig. 2 (b). Structure of a coaxial stranded cable is suitable to relieve the bending stress for the large bore cable. The bending strain of the tight-twisted cable can be explained by the Eq. (1).   In the loose-twisted cable, bending strain will decrease, because the slip among the strands to the axial direction will compensate the outside tensile stress with inside compressive stress. In a coaxial flexible stranded cable, total number of the strands, N, and diameter of the cable, D, can be expressed as N = 3n(1+n)+m(1+n)       ( 2 ) andD = (k+2n)d        ( 3 ) where, n is number of layers, m is number of strands of the core, k is constant and value related to m. When m is 3,  k becomes 2.155. In the cable design, parameters of m and n are selected to 3 and 12, respectivelly. The diameter of the strand, n, is 1.3 mm as shown in Fig. 2 (a). To decrease the bending strain, a twist ratio (�one pitch length / cable diameter) is also determine to be 30.  Main parameters of 10 kA MgB2 cable are summarized in Table 2. Reference [1] Y. Hishinuma et al, CSJ Conference , May 13, 2009 1D-a10. [2] S. Yamada et al, Journal of Physics: Conference  Series 97 (2008) 012167. 125§13. Conceptual Design of 10 kA Class MgB2 Cable for Hybrid Energy Transfer LineYamada, S., Hishinuma, Y.

Conceptual Design of 10 kA Class MgB2 Cable for Hybrid Energy Transfer Line

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