• Progress in Superconductivity and Cryogenics
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• v.23 no.4
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• pp.10-13
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• 2021

Recently, cable conductors composed of numerous coated conductors have been developed to transport huge current for large-scale applications, for example accelerators and fusion reactors. Various cable conductors such as CORC (Conductor on round core), Roebel Cable, and TSTC (Twisted stacked tape cable) have been designed and tested to apply for large-scale applications. But, these cable conductors cannot improve the engineering critical current density (J_e) because they are made by simple stacking of coated conductors. In this study, multi-HTS (High temperature superconductor) layers on one substrate (MHOS) wire was fabricated to increase the engineering critical current density by using the exfoliation of superconducting layer from substrate and silver diffusion bonding method. By the repetition of these processes, the 10 m long 6-layer MHOS conductor was successfully fabricated without any intermediate layers like buffer or solder. 6-layer MHOS conductor exhibited a high critical current of 2,460A/12mm-w. and high engineering critical current density of 1,367A/mm² at liquid nitrogen temperature.

• Transactions on Electrical and Electronic Materials
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• v.5 no.2
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• pp.55-60
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• 2004

High-temperature Superconductor(HTS) tubes were fabricated in terms of different chemical compositions and various SrSO$_4$additions by centrifugal forming method. For powder melting by induction the optimum range of melting temperatures and preheating temperature were 1050$^{\circ}C$, 1100$^{\circ}C$ and 550$^{\circ}C$ for 30 min, respectively. The mould rotating speed was 1000 rpm. A tube was annealed at 840$^{\circ}C$ for 72 hours in oxygen atmosphere. The plates like grains more than 20 $\mu\textrm{m}$ were well developed along the rotating direction of mould regardless of initial chemical compositions and the amounts of SrSO$_4$in Bi2212. The specimen with Bi2212 composition exhibited T$\_$c/ of 83 K, while the specimens fabricated with other compositions are lower than 60 K. The measured I$\_$c/ and J$\_$c/ at 77 K(B = 0 T) in Bi2212 with 7 % SrSO$_4$ composition were about 680 A and 380 A/$\textrm{cm}^2$.

• Progress in Superconductivity and Cryogenics
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• v.12 no.4
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• pp.31-35
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• 2010

In superconducting magnet applications, winding methods of the superconducting magnet can be classified into a layer winding and a pancake winding. The superconducting magnet using high temperature superconductor (HTS) with rectangular shape is generally fabricated using the pancake winding method. On the other hand, low temperature superconducting (LTS) magnet may be wound by either a pancake winding or a layer winding. Compared with the layer winding, the pancake winding method has a merit of easy replacement of a damaged pancake module, but it also has a demerit of requirement of splicing between each double pancake modules. In this paper, we investigated characteristics of the layer and pancake winding methods using HTS. Six samples were wound out of BSCCO and Coated Conductors (CCs) by two winding methods and their characteristics were experimentally observed.

• KEPCO Journal on Electric Power and Energy
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• v.1 no.1
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• pp.157-162
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• 2015

Large scale superconducting magnetic energy storage (SMES) system requires very high magnetic energy density in its superconducting coils to enhance the energy capacity and efficiency of the system. The recent high temperature superconducting (HTS) conductors, so called 2G conductors, show very good performance under very high magnetic field so that they seem to be perfect materials for the large scale SMES coils. A general shape of the coil system with the 2G HTS conductor has been a tor oid, because the magnetic field applied perpendicularly to the surface of the 2G HTS conductor could be minimized in this shape of coil. However, a toroid coil requires a 3-dimensional computation to acquire the characteristics of its critical current density - magnetic field relations which needs very complicated numerical calculation, very high computer specification, and long calculation time. In this paper, we suggested an analytic and statistical calculation method to acquire the maximum magnetic flux density applied perpendicularly to the surface of the 2G HTS conductor and the stored energy in the toroid coil system. Although the result with this method includes some errors but we could reduce these errors within 5 percent to get a reasonable estimation of the important parameters for design process of the HTS toroid coil system. As a result, the calculation time by the suggested method could be reduced to 0.1 percent of that by the 3-dimensional numerical calculation.

• Journal of the Institute of Electronics Engineers of Korea TE
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• v.37 no.1
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• pp.70-78
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• 2000

In applying high-${\underline{T_c}}$ superconducting material to microwave devices, Uncertainty of electromagnetics of high-${\underline{T_c}}$ superconductor(HTS) and the temperature dependence of the substrate fits with HTS thin film cause difficulty in realization of such antenna for industrial applications. It must be noted to characteristic the HTS antenna in contrast with normal conducting counterpart for this real application. In this paper, a comparative study between HTS microstrip antennas and gold antennas was reported in terms of the return loss, the characteristic impedance, efficiency, and other various characteristics. HTS thin films were $YBa_2Cu_3O_{7-x}$ (YBCO) on MgO substrates. Superconducting microstrip antennas used in this work were to directly inset a microstrip transmission line into the 50 ${\Omega}$ region of the radiating patch. Measurement results of HTS antennas and gold antennas showed that usable antennas can be made using this architecture.

• Progress in Superconductivity and Cryogenics
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• v.13 no.1
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• pp.12-16
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• 2011

In this paper, the prototype of the HTS motor with an on-board cryocooler, is fabricated and tested. The overall system is composed of the stator with conventional copper winding, the rotor with superconductor, and the rotating cryocooler designed from the on-board concept. The rotor is fabricated as the race-track coil with 2G, YBCO tape and contacts with the on-board cryocooler while being rotated together. An inline-type pulse tube refrigerator is used as the on-board cryocooler. The cryocooler is fabricated from optimal process to satisfy the structure and thermal stability of the on-board system. Each component is integrated according to carefully defined sequence. Specially, a combining method of torque tubes is an important part for sustaining stability of the rotor and the cryocooler. In the rotating test, the HTS motor is successfully operated with 240 rpm of rotating speed when 75 A current is supplied to the superconducting rotor. In this paper, potential problems of the HTS motor system using the on-board cryocooler are proposed and solved, and realistic possibility of this concept is also confirmed.

• Progress in Superconductivity and Cryogenics
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• v.21 no.1
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• pp.25-30
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• 2019

This paper presents a conceptual design approach of air-cored synchronous machine with high temperature superconductor (HTS) field winding. With a given configuration of a target machine, boundary conditions are set in the cylindrical coordinate system and analytic field calculation is performed by solving a governing equation. To set proper boundary conditions, current distributions of the field winding and the armature winding are expressed by the Fourier expansion. Based on analytic magnetic field calculation results, key machine parameters are calculated: 1) inductance, 2) critical current of field winding, 3) weight, 4) HTS conductor consumption, and 5) efficiency. To investigate all potential design options, 6 sweeping parameters are determined to characterize the geometry of the machine and the parameter calculation process is performed for each design options. Among design options satisfying constraints including >80 % critical current margin and >95 % efficiency, in this paper, a first-cut design was selected in terms of overall machine weight and HTS conductor consumption to obtain a lightweight and economical design. The goal is to design a 5-MW machine by referring to the same capacity machine that was previously constructed by another group. Our design output is compared with finite element method (FEM) simulation to validate our design approach.

• Progress in Superconductivity and Cryogenics
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• v.11 no.1
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• pp.16-19
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• 2009

Recently, for improvement of the magnetic field of high temperature superconductor (HTS) apparatus, many studies investigating on operating in the range of $20{\sim}65K$ with liquid helium or the conducting method using cryocooler is actively reviewed. Also, the cooling method using solid nitrogen as cryogen is being suggested. Since the nitrogen has very large specific heat in solid state, it is expected that it can enable long time operation without a continuous supply of cooling energy. However, there is still insufficient data on the characteristics of solid nitrogen such as thermodynamic properties and liquid-solid phase change. Especially, there was almost no study done on the electrical insulation properties of solid nitrogen so far. In this study, solid nitrogen to find the electrical characteristics was made by using cryocooler and cryostat, and investigated the flashover discharge and breakdown. The results of this study will be useful as a basic data for electrical insulation design of the HTS system using solid nitrogen as cryogen.

• Progress in Superconductivity and Cryogenics
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• v.21 no.1
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• pp.1-5
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• 2019

The pulsed field magnetization of the short-circuited soldered double pancake coil made of stabilized commercial high-Tc superconductor (HTS) tape is experimentally studied. The evolution of the shielding current induced by the pulsed field and the trapped field after the pulsed magnetization was measured at 77 K. It is shown that the trapped field in the coil is close to the value reached in the field cooling process and reduces weakly at 5-fold increasing of pulsed field amplitude. The current relaxation at t~2 ms after the pulse is defined by the current sharing between the tape's copper coating and the $YBa_2Cu_3O_{7-d}$ layer. In the intermediate time scale (1 s < t < 100 s) the flux creep in HTS layer dominates. At t > 100 s the current's relaxation is defined by the resistance of soldered joint between tapes.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.19 no.4
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• pp.333-338
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• 2007

The object of this study is to find the optimal insulation design conditions of a HTS power cable cryostat. The optimum condition of a cable cryostat is obtained by varying types of MLIs, cable core weights, spacer diameters, winding pitches and MLI layer numbers. As the weight of cable core is increased, conduction heat transfer from surroundings to cable cryostat is increased. But as the spacer pitch is increased from 120 mm to 200 mm, the heat leak of cable cryostat remains almost constant. The optimal number of MLI layers is suggested. Double ply MLI is more effective than triple ply MLI and the insulation effect is best when the number of MLI layers is 36.