Fig. 2. Cross sectional view of a DC SC cable rating 4 kV 250 kA. Each circuit of SC cable system has five terminations on the solar cell array, and its rating current increases at each termination. Dimensions of the cables are varied depending on the rating. Figure 2 shows the cross sectional view of the designed cable and a general description of its largest portion is shown in Table 1. The largest outer diameter is designed to be 130 mm (5.1 in.) and the allowable bending radius is estimated to be smaller than ten times that diameter. The selected superconductor is aluminum stabilized niobium titanium. The overall current density is designed to 250 A/mm2 at the rating. The positive and negative conductors are laid coaxially to suppress the magnetic field outside the cable, and enclosed in aluminum corrugated tubes, which will be used as the coolant ducts. The maximum electromagnetic force per unit area estimated at the inner conductor is 31 kgf/cm2 (440 psi), and these ducts must be strong enough to endure against this force. Although electric insulation by the coolant itself, supercritical helium, makes the cable connections simple, tape wrapped insulation is chosen to obtain smaller outer diameter.
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