BSCCO Wire Research Articles

Mechanical—electromagnetic property of stainless sheet laminated BSCCO–2223 wires

In order to elucidate the effect of applied tensile stress/strain on the critical current of DI-BSCCO-2223 wires, the critical current measurement and the tensile test were carried out at 77 K. Neutron diffraction measurements were also performed at 77 K to get direct information about the local strain exerted on the BSCCO superconducting filaments. It was reported that the critical current of BSCCO wires decreases linearly in a small range of tensile stress/strain and that the critical current returns reversibly on reducing the stress/strain. The gradual decrease of critical current was observed within the reversible region. When the tensile stress /strain increased beyond a characteristic value, the critical current decreased rapidly due to the brittle fracture of BSCCO filaments. It is proposed that the reversible stress/strain limit of critical current (Rrec and Arec) can be defined experimentally as the 99% Ic recovery stress (R99%rec) and strain (A99%rec). The reversible strain limit is proposed to consist mainly of three factors of pre-strain, thermal strain and tensile fracture strain of SC filaments themselves. The calculated relation between the Rrec and Arec could well explain quantitatively the observed relation between 99% Ic recovery stress and strain.

AC Loss Measurements in a Hybrid REBCO/BSCCO Coil Assembly

Wire cost and ac loss are paramount issues for the future uptake of high-temperature superconductor (HTS) ac machines. In particular, new approaches which reduce the total manufacturing cost of HTS coils are critical to the future commercial uptake of HTS technology. Here, we present the results of ac loss measurements of a hybrid HTS coil assembly comprising end windings (EWs) wound with BSCCO wire and a central winding (CW) wound with REBCO wire. As a cost mitigation measure, we have chosen to use REBCO wire which possesses a relatively low self-field $I_{{\rm{c}}}$ at 77 K, equating to approximately half that of the BSCCO wire. Transport ac loss measurements were made on the total coil assembly at both 77 K and 65 K, using a recently developed lock-in amplifier approach. We show the ac losses in the assembly at these temperatures scale with the overall transport critical current threshold of the hybrid coil assembly. The results are then compared with a reference coil assembly having similar geometrical dimensions, and in which both the EWs and CW were wound with identical BSCCO wire. Surprisingly, we observe that the ac loss of the hybrid coil is lower than that of the BSCCO coil, despite the CW of the hybrid coil employing wire a lower overall average $I_{{\rm{c}}}$ . We attribute this effect to the lower ac loss of coated conductor REBCO wire under parallel field, which is the dominant field orientation in the CW region. Based on this observation, we conclude that the hybrid assembly design is a good design strategy for HTS coil assemblies, enabling both wire cost and ac loss to be balanced.

Performance and Analysis of No-Insulation HTS Toroidal Magnet

As Tokamak toroidal field (TF) coils operate at a high magnetic field and experience a variety of transient heating loads, the applicability of no-insulation (NI) techniques to wind the TF coil is taken into consideration here in an effort to secure high current density and high thermal stability. This paper presents the construction and test results of a NI high temperature superconducting (HTS) toroidal magnet. We fabricated the magnet using BSCCO wire manufactured by Sumitomo. The magnet consists of ten racetrack double pancake (DP) coils. Each DP coil was tested separately in liquid nitrogen at 77 K to obtain its critical current and characteristic resistance, then, after assembly and soldering, the magnet was tested at 77 K to measure the variations in voltage and magnetic field during charging, discharging, and current disturbancing. Finally, we discuss the thermal runaway behavior of the toroidal magnet during overcurrent operation as well as the influence of the quenched coil on the other coils in the system.

AC loss measurements in HTS coil assemblies with hybrid coil structures

Both AC loss and wire cost in coil windings are critical factors for high temperature superconductor (HTS) AC machinery applications. We present AC loss measurement results in three HTS coil assemblies at 77 K and 65 K which have a hybrid coil structure comprising one central winding (CW) and two end windings (EWs) wound with ReBCO and BSCCO wires with different self-field Ic values at 77 K. All AC loss results in the coil assemblies are hysteretic and the normalized AC losses in the coil assemblies at different temperatures can be scaled with the Ic value of the coil assemblies. The normalised results show that AC loss in a coil assembly with BSCCO CW can be reduced by using EWs wound with high Ic ReBCO wires, whilst further AC loss reduction can be achieved by replacing the BSCCO CW with ReBCO CW. The results imply that a flexible hybrid coil structure is possible which considers both AC loss and wire cost in coil assemblies.

Reversible stress and strain limits of the critical current of practical REBCO and BSCCO wires

Practical REBCO and BSCCO-2223 tape-shaped wires are now manufactured on an industrial scale. They are a typical composite material consisting of superconducting layer/filaments together with functional components. These functional components affect directly the stress and strain dependences of the critical current. When applying an external stress R, the critical current Ic was measured. Then the external stress was reduced to R = 0 and the recovered critical current Icr was again measured. The tensile stress and strain dependences of both normalized critical currents divided by the original value, Ic/Ic0 and Icr/Ic0 were investigated. In general Icr/Ic0 recovered close to unity when the applied stress was low, but its recovering level decreased gradually with increasing applied stress. The definition of the reversible stress and strain limits was investigated and its validity was proved using the cyclic loading test. The original definition of reversible stress and strain limits of critical current relates to: (1) when releasing the applied stress and strain, the Ic shall recover to the original value, and (2) when applying the cyclic stresses, the Ic shall keep the original value. Here, as a practical definition for the reversible stress and strain limits, the tensile stress and strain at 99% recovery of Ic have been proposed. On the other hand, it was made clear that the stress and strain at Ic 95% retention are not valid for use commonly as a criterion of reversible stress and strain limits for both practical REBCO and BSCCO-2223 wires.

Construction and the Circulation Test of the 500-m and 1000-m DC Superconducting Power Cables in Ishikari

A demonstration project of the dc superconducting power transmission line using the BSCCO wires was started in Ishikari, Japan as a national project (Ishikari project) from 2013FY. In the project, two power lines have been installed. Line 1 connects a photovoltaic power plant and an Internet data center by a 500-m underground cable for practical use, whereas line 2 with a 1000-m cable will be used for verification tests. In this project, we developed a new design of an adiabatic double tube with reduced heat leaks, i.e., <;1.5 W/m. We have also adopted the Peltier current lead that drastically cuts heat transfer at the cable terminal below 35 W/kA. To control the thermal contraction and expansion of the cable to avoid its breakage, we adopted two techniques, namely, a movable cryostat and a helical deformation technique. The construction was started in the field in June 2014 and completed at the end of April 2015 for line 1. Then, we performed the first cooling test for line 1 from May to June in 2015, during which we have confirmed that the thermal performance is as good as what we designed, and the current of 5 kA was successfully transported.

Electrical Characteristic Analysis According to Contact Resistance Between Turns of HTS Coil

This paper presents our analysis of the output characteristics of a high-temperature superconductor (HTS) coil depending on the turn-to-turn contact resistance. Important design factors were investigated by taking into account the turn-to-turn contact resistance based on the analysis results. Analyses were performed on five self-fabricated coil models with different turn-to-turn contact resistances. To consider only the turn-to-turn contact resistance, we used a first-generation HTS BSCCO wire with simpler architecture and mechanical properties than the second-generation HTS wire. From this study, it was confirmed by experiment that as the turn-to-turn contact resistance decreases, the electrical stability increases but the output efficiency decreases compared with the input.

Current Limiting Performance of Transformer-Type Superconducting Fault Current Limiter Made of BSCCO and REBCO Wires

Superconducting fault current limiters (SFCLs) are expected to be installed in the power system for fault current limitation and improvement of power system stability. Among various SFCLs, we have proposed the transformer-type SFCL that produces limiting reactance for smaller fault currents and, additionally, gives limiting resistance for larger fault currents. Therefore, the transformer-type SFCL shows better recovery performance than resistive-type SFCLs. In this paper, we fabricated two transformer-type SFCLs using different high-temperature superconducting wires [Bi-2223 (BSCCO) wire and GdBCO, which is a kind of rare-earth-barium-copper-oxide (REBCO) wire] for the secondary coils and compared their current limiting characteristics. They were designed under the condition that the specifications of the primary coils and their trigger current level are about the same, respectively. As a result of comparing their current limiting characteristics, the transformer-type SFCL using GdBCO wire for the secondary coil shows a larger limiting reactance and dissipates less energy. Therefore, the transformer-type SFCL using GdBCO wire for the secondary coil shows better recovery performance.

Low-Temperature Scaling of the Critical Current in 1 G HTS Wires

We present highly detailed temperature, magnetic field and field angle dependent measurements of the critical current of a state-of-the-art commercial first-generation Bi-2223 high temperature superconductor wire (Sumitomo new type H high current density DI-BSCCO). By scaling the applied field values at different angles using the Blatter electron mass anisotropy expression, we demonstrate that the measurements at each temperature from 20 to 85 K collapse onto a common curve with respect to the scaled magnetic field. However, the scaling parameter is found to range from 7 at 80 K to 13 at 25 K, far below the values reported in the literature for the electron mass anisotropy of this material, and far closer to the values reported for similar analyses of data obtained from the much less anisotropic superconductor YBCO. This suggests that a mechanism of similar magnitude underlies and determines the results obtained for both materials in spite of their greatly differing electronic mass anisotropies. By normalizing the results to the self-field critical current and the irreversibility field, we are able to obtain a single universal curve describing the performance of the superconductor across the full range of operating conditions. In contrast to pinning-engineered YBCO coated conductors, we find that the low-temperature behavior of BSCCO wires can be well correlated with its high-temperature behavior. Knowledge of this straightforward behavior of this commercial superconductor across the full parameter space of temperature, field and field angle will be invaluable to engineers working with this material to construct machines or devices.

Influence of Various Voltage Leads on AC Loss Measurement in a Double Layer BSCCO Conductor

We have operated the two 22.9 kV/50 MVA HTS cable systems installed at Gochang Test Yard and Icheon Substation of Korea Electric Power Corporation (KEPCO), respectively; they have a double layer conductor and a single layer shield, consisting of BSCCO and YBCO-NiW wires. In general, the ac loss of a multilayer cylindrical conductor like the KEPCO HTS cables is evaluated from the conductor's current and the loss voltage of a lead soldered onto its outermost layer. To experimentally investigate what the voltage lead on the outermost layer picks up in this study, we prepared a double layer BSCCO conductor sample, and attached the four voltage leads of the outer, inner, contactless, and total leads. Then its ac loss for these leads was examined for different layer current distribution, and finally compared with a numerically calculated one. The results show that the outer-lead, which is often used in the double layer conductors, takes only the outer layer's loss voltage like the contactless-lead. Therefore, for ac loss evaluation of our double layer sample, a new voltage lead, total-lead, is presented besides the conventionally used outer-lead. The total-lead best fits with the numerical calculations, regardless of layer current distribution. However, the outer-lead is not suitable, especially for nonuniform distribution, although it still now is valid only for uniform distribution.

Experimental Investigation Into the Characteristics of Micro-SMES' Magnet

Superconducting magnet is a key component of Superconducting Magnetic Energy Storage (SMES), so it is necessary to investigate into the characteristics of superconducting magnet before the SMES run in power system. In the paper, a superconducting hybrid magnet based on YBCO wires and BSCCO wires, which were from Superpower and American Superconductor Company respectively, was designed and produced, and then through the cooling test, critical current test, energy storage test, ground insulation test and exchanging power experiments with power system, the electrical specifications and low temperatures insulating performance of the superconducting magnet were investigated. The results proved that the performance of the hybrid magnet satisfied the design requirements.

The Cooling and Safety Design of a Pair of Binary Leads for the MICE Coupling Magnets

The key to being able to operate the superconducting solenoids in the Muon Ionization Cooling Experiment (MICE) using cryocoolers running at around 4.2 K is the application of high temperature superconducting (HTS) leads. Because the MICE magnets are not shielded, all of them will have a stray magnetic field in the region where the coolers and the HTS leads are located. The behavior of the HTS leads depends strongly on the HTS material used for the leads, the magnetic field and their warm end temperature. A pair of binary leads consisting of copper leads and HTS leads made from oriented multiple strands of BSCCO wires will be used for electrical transfer of the MICE coupling magnet for the purpose of reducing the heat leak through the leads to 4.2 K region. This paper mainly discusses the detailed design of the HTS leads and their cooling. Protection for the HTS leads during a power failure is discussed as well.

Design, Fabrication, and Performance Tests of a HTS Superconducting Dipole Magnet

The use of HTS (high-temperature superconductor) coils for accelerator magnets decreases significantly the power consumption and operating cost. Therefore, a preliminary study was launched and a prototype of a dipole magnet with HTS coils has been designed and fabricated by NSRRC and HTS-110 Ltd. Although 2G YBCO wire is expected to be used in future HTS applications, it currently requires more joints to form the completed coils. For this reason, we chose 1G BSCCO wires for the HTS coils. Two single-stage pulse-tube refrigerators with one compressor serve to cool the HTS coils of the magnet, but we shall use LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> to replace the pulse-tube refrigerators in the future. The HTS magnet is designed to provide a stable field of strength 1.19 T with field homogeneity better than 1.5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> in the range of the transverse -20 ≤ x ≤ 20 mm direction when it operates at 50 K with a current of 110 A. To compare with the field features of copper-coil dipole magnets, a Hall-probe measurement system was used to measure the detailed magnetic field and B-I characteristics of the HTS dipole magnet at NSRRC.

Recent progress on improvement to mechanical properties of DI-BSCCO wire

To improve the mechanical properties of silver-sheathed BSCCO wire, the laminated BSCCO wires with stainless steel were made under some experimental conditions. The dependence of the stainless steel thickness and the dependence of the pre-tension of stainless steel tapes on the laminated BSCCO were investigated by mechanical tests (tensile test at 77 K and RT and double-bending test at RT) using short samples. Due to the difference of the coefficient of thermal expansion (CTE) and the relaxation to equilibrium after removing the total pre-tension of no laminated BSCCO (insert tape) and stainless steel tapes, the residual axial compressive strain applies to an insert tape after the lamination process. A high compressive strain up to the compressive yield of the silver-alloy is so useful for improvement of the mechanical properties of BSCCO wire. Measurement results were approximately the same as the simple model calculated from the residual strain applied to an insert tape by the difference of CTE and pre-tension. The stainless-steel-laminated BSCCO wire ‘Type HT-SS’ has been able to be achieved over 500 MPa at 77 K by increasing stainless steel thickness and the residual axial compression for an insert tape. The developed tough DI-BSCCO has a higher hoop force to compare with YBCO-coated conductor using Hastelloy substrates under the same circumstances such as magnetic field, winding diameter and transport current.

Current Limiting and Recovery Characteristics Under Load of Transformer Type SFCL with Rewound Structure Using BSCCO Wire in Model Power System

Abstract We have proposed new design of a transformer type SFCL with primary and secondary superconducting coils which has rewound structure. For not so large fault current, the proposed SFCL limits the current by the inductive component by the normal transition of the flux shielding coil (secondary), and for larger fault current, it can give the resistive component additively by the normal transition of the primary coil. The recovery characteristics under load condition and repetitive limiting operation were experimentally investigated in a laboratory scale power system. The SFCL limited twice repetitive faults current and recovered quickly under load condition.

Pinning Force Anisotropy for HTS Wires

We investigate the pinning force anisotropy for BSCCO and YBCO commercial wires at 77 K. The pinning force is measured to 3 T and for all field angles. We show that the magnitude of the pinning force maximum as a function of applied field angle follows known statistical functions. The position of the maximum with field also follows these functions. This is a step towards a Dew-Hughes type scaling covering field, field angle and temperature for HTS wire.

Current Limiting Experiment of Transformer Type Superconducting Fault Current Limiter With Rewound Structure Using BSCCO Wire in Small Model Power System

Superconducting fault current limiters (SFCLs) are expected to improve the reliability and stability of power systems. We have proposed new design of a transformer type SFCL whose primary and secondary superconducting coil has rewound structure. The fundamental characteristics of the proposed SFCL were investigated using a small model designed and made with BSCCO wire. This paper describes on the power system characteristics of the proposed SFCL with rewound structure. The basic experiments were carried out by use of the model SFCL in a laboratory scale power system (one-machine and infinite bus system). It was confirmed that the proposed SFCL successfully limited the fault current and suppressed the voltage drop of the generator and recovered quickly even in repetitive limiting operation.

Magnetic Field and Critical Current of a BSCCO HTS Magnet at Various Aspect Ratios

When the length of wire used to make an HTS magnet is fixed, the magnetic properties of the HTS magnet including the central magnetic field and stored energy mostly depend on the aspect ratio of the HTS magnet. This paper presents calculations of the magnetic properties of a BSCCO HTS magnet at various aspect ratios. The HTS magnet was assumed to be made by pancake windings. The total length of the BSCCO wire was varied from 2 to 10 km. For a specific length of the BSCCO wire, the number of pancake windings was varied up to 70. The inner diameter of the HTS magnet was fixed to be 50 mm and 77 K. When the length of the BSCCO wire was 2 km, the central magnetic field was maximum when 34 pancake windings were used. The maximum central magnetic field and the current of the HTS magnet were 859.3 mT and 21.8 A, respectively. The number of turns of a single pancake winding and the aspect ratio of the HTS magnet were 171 turns and 2.54, respectively.

Study on the Transport Current Characteristics of YBCO Coated Conductor According to Stabilization Layer

The analysis of the steady and transient states is very important for the application of the superconducting wire to electric devices. Through many studies, the detailed evaluation technology for BSCCO wire, referred to as “the first-generation superconducting wire,” has been established to some extent. Meanwhile, the detailed analysis of the steady and transient states of YBCO thin-film wire, the second-generation wire that is increasingly being applied to more electric devices, is insufficient. Accordingly, in this study, the quench behavior at a below-critical temperature was evaluated, especially in the flux flow state, using two types of commercial YBCO thin-film wires, to determine the electric devices to which the wire can be applied, and to define its operating conditions. For this, YBCO thin-film wires with copper and stainless-steel stabilizer layers, which were manufactured considering the specific resistance and conductivity of the stabilizer layer, were prepared. The critical currents of the two wires were 85 A and 70 A, respectively, but their critical temperatures were identical at 90 K. The resistance values of both wires increased over time, within the range above the critical temperature, but they were different within the range below the critical temperature, according to the stabilizer layer. This can be an index that clearly represents the conducting and current-limiting characteristics of YBCO thin-film wire. Therefore, in this study, the two wires' current division characteristics were examined within the temperature range of 77 K (at which the liquid nitrogen starts to boil) to 90 K (the critical temperature) to determine which of the two wires was the conduction wire and which was the current-limiting wire. In addition, the conduction region was defined based on the trend of increase resistance below and above the critical temperature.

Quench Detection Method of HTS Model Coil Using a Series-Type Thermocouple

This paper proposes a quench detection method applied to a HTS coil and also discusses the results of tests on an HTS BSCCO wire and an HTS YBCO coil. A series-type thermocouple was fabricated to detect quench, where several thermocouples were welded in series. As the series-type thermocouple has many points of detection, variation in temperature was detected at each point by using thermo-electromotive force. The feasibility of the proposed method was investigated through the quench detection tests on the YBCO coil. This method has advantages such as a simple structure and cost effectiveness and also protects the HTS coil by detecting partial quench and its propagation.