A Study On Electrical Characteristics Of Twisted Soldered-Stacked-Square (3S) Wires Consisting Of HTS Narrow Tapes With 1 Mm Width

External magnetic field would influence the performance of HTS wires including critical current,AC loss and so on,especially when the magnetic field is perpendicular to the HTS wire's surface.In order to reduce the effect of external magnetic field,many studies have been done,which mainly focus on stack or twist multifilament structures: tapes stacked and transposed according to the Roebel Assembled Coated Conductors technique,tapes stacked and twisted along the longitudinal direction,round strand composed of coated conductor cable and so on.However,these studies are usually based on HTS tapes with more than 4 mm width,and their dimensions are significantly limited by the widths of the HTS tapes used in fabrication.Different from above studies,we proposed a novel wire with a square cross section of 1 mm × 1 mm which is named Soldered-Stacked-Square(3S)HTS wire.Due to the low width-to-thickness ratio and small square dimension,3S HTS wire has great advantages in cabling,but it is inevitable to endure twisting in actual applications.Therefore,it is necessary to have further study on the twist structure of 3S HTS wire.In this paper,we investigate the basic electrical characteristics for the twisted 3S HTS wires: twist pitch,critical current,self-field AC loss and so on.We firstly fabricate several 3S HTS wire samples,(2+7)-wire samples through narrowing,soldering and stacking process,and then twist the samples with different twist pitches.The entire fabrication process will be introduced in detail.Then we study the critical current characteristics versus twist pitch of the(2+7)-T-wire.Furthermore,we investigate the self-field AC loss characteristics of the(2+7)-T-wire,including dependence on frequency and twist pitch.It is shown that the critical current of twisted single 3S wire is constant up to a twist pitch of 90 mm,and the minimum twist pitch is approximately 60 mm.Besides,the minimum twist pitch of twisted double 3S wires is approximately 100 mm.Measured AC losses are independent of frequency and are in good agreement with the thin strip theoretical values.Besides,the measured self-filed AC losses of twisted 3S wire and 3S wire are almost identical.The electrical characteristics of twisted 3S wire are satisfied for HTS applications.