HTS Wire Research Articles

Changes in the Thermal Stability of 2G HTS Wires by Local Modification of the Stabilization Layer

In order to use 2G HTS wires in superconducting devices, it is important to understand the origin of thermal instabilities in these materials. Previous results showed that inhomogeneities in the critical current distribution are not the only factor that determines the heat generation distribution along the sample when the current exceeds the critical value. In this work, different types of controlled defects have been generated in the Cu-layer using laser ablation. In all cases, laser parameters have been chosen while assuring that the critical current of the superconductor does not deteriorate. It has been obtained that even if the thickness of the stabilizing layer is reduced from 20 μm to less than 10 μm in some regions, the sample response to overcurrents is not modified.

Novel Self-Limiting Transformer With Active Magnetic Short Circuit Using Perfect YBCO Wire Loops

In this paper we present a new arrangement implementing a novel self-limiting transformer. We have developed a 1-phase model. We used a 3-limb transformer for one phase and we surrounded 2 limbs of the three, the primary and the secondary coils, with a common perfect closed YBCO loop. In this way we could realize the active magnetic short circuit which gives a new possibility for novel applications. Its operation is based on the principle of the magnetic flux conservation in a closed loop. This is a well-known physical law but so far not applied in this way. We used perfect closed YBCO wire loops with parallel turns. The paper presents the results of our experiments and opens new advanced applications of the perfect YBCO loops made of HTS wire. We considered the efficiency and significance of the perfect closed loop made from YBCO wire.

Hysteresis Loss in Power Cables Made of 2G HTS Wires With NiW Alloy Substrate

2G HTS wires produced with the MOD/RABiTS process with NiW substrates have weak magnetism and therefore extra losses in a substrate. The goal of this paper is to find out the model that could describe losses just in a substrate only. Two and three dimensional numerical electromagnetic field analysis has been developed for two-layer cables made of 2G HTS conductors with magnetic substrates. Two arrangements were used for the 2G conductors between the inner and outer layers: tape-on-tape and tape-on-gap. Comparisons of calculations with measured ac loss are presented.

Electrical and Mechanical Characterizations of Nanocomposite Insulation for HTS Systems

As HTS wire technology continues to advance, a critical need has emerged for dielectric materials that can be used in superconducting components such as terminations, fault current limiters, transformers, and motors. To address this need, CTD is developing nanocomposite insulations based on epoxy and benzoxazine chemistries. Depending on part geometry, some processing methods are more efficient than others. For this reason, CTD is investigating both fiber-reinforced and filled resin systems for use in these applications. A thorough set of electrical testing including AC breakdown, breakdown as a function of thickness, and flashover shows promising performance characteristics. In addition, mechanical testing (short beam shear and compression) indicate that these new materials to have as good or better performance than G10.

Study on Method to Suppress Decay of Trapped Magnetic Fluxes in the HTS Bulk Subjected to Perturbation of External Magnetic Field by Use of Shielding Coil Wound of HTS Wire

Trapped magnetic fluxes in HTS bulks are decayed when the bulks are subjected to perturbation of external magnetic fields. In HTS bulk apparatuses such as HTS bulk motors and magnetic levitation bearings, there is a possibility that the trapped magnetic fluxes in the bulks disappear because the bulks are inevitably subjected to perturbations of the external magnetic fields. For those apparatuses to work stably and reliably, it is necessary to develop methods to suppress the decay. It was shown in our previous experiments that the decay is caused by temperature rises of the bulks due to AC losses in the bulks. The authors proposed a method to put a shorted shielding coil wound of HTS wire around the bulk aiming at reduction of the AC losses in the bulk. It was experimentally shown by use of a shielding coil wound of Bi/Ag sheathed wire that the decay of the trapped magnetic flux was effectively suppressed. In this paper, shielding performance of the coil wound of GdBCO wire was experimentally investigated comparing with that of the coil wound of Bi/Ag sheathed wire. AC losses in the bulks and shielding coils are calculated for various arrangements of the shielding coil to find a preferable shielding coil arrangement from stand points of shielding performance and reduction of AC losses.

이종초전도 코일을 이용한 하이브리드형 한류기의 제작 및 단락실험

Hybrid fault current limiters (FCL) have been researched at Yonsei University. The hybrid FCL has advantages such as having a rapid response to a sudden fault situation and a fast recovery time from a quench. It consists of an asymmetric HTS coil, a switching module, and a bypass reactor. The asymmetric HTS coil is wound with two different types of HTS wires in an opposite direction so that it has nearly zero inductance at the superconducting state. When the quench occurs at the fault state, a strong magnetic field is generated from the asymmetric coil because of different quench characteristics of two HTS wires, and then a repulsive force is induced in the switching module. The force opens the switch and the fault current is pushed into the bypass reactor. In this research, we analyzed the cause of the repulsive force and confirmed, experimentally and computationally, that the magnitude of a repulsive force is varied by changing the gap distance between the asymmetric coil and the switching module. By using the FEM simulation, we calculated the repulsive force with respect to the gap distance and verified that the effect of the gap distance. Then, short circuit test was carried out to confirm the correct operation of the fast switch.

Simulation and experiment of a YBCO SMES prototype in voltage sag compensation

This paper gives a introduction of a SMES unit using 2G HTS wires. A complete SMES system including both superconducting coils and control circuit has been designed to operate at 77 K. Three single-phase H-bridge converters have been used in the control circuit. A loop control signal is sent out by using 32 fixed point Digital Signal Processor (DSP). The complete circuit has been both modelled in simulation and built experimentally. The results validate that this SMES successfully compensates a voltage sag in a power system.

Study of shunt type SFCL equipped with electromagnetic repulsion switch for large capacity

AbstractUsing a high‐temperature superconductor, we constructed and tested a model Superconducting Fault Current Limiter (SFCL). The SFCL that we proposed has a vacuum interrupter with electromagnetic repulsion mechanism. We set out to construct a high‐voltage‐class SFCL. We produced an electromagnetic repulsion switch equipped with a 24‐kV vacuum interrupter (VI). However, the opening speed becomes slower, because the larger vacuum interrupter needs a heavier‐weight contact. For this reason, the current which flows in a superconductor may not be interruptible within a half cycle of current. In order to solve this problem, it is necessary to change the design of the coil connected in parallel and to strengthen the electromagnetic repulsion force at the time of opening the vacuum interrupter. Thus, the design of the coil was changed, and in order to examine whether the problem is solvable, a current limiting test was conducted. We carried out a current limiting test using second‐generation (2G) HTS wire. The element used in this experiment has a stainless steel stabilizer on both sides of the wire. In the experiment we succeeded in interrupting the current of a superconductor within a half cycle. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 173(4): 20–27, 2010; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21039

Design and manufacture of a toroidal-type SMES for combination with real-time digital simulator (RTDS)

The authors designed and manufactured a toroidal-type superconducting magnetic energy storage (SMES) system. The toroidal-type SMES was designed using a 3D CAD program. The toroidal-type magnet consists of 30 double pancake coils (DPCs). The single pancake coils (SPCs), which constitute the double pancake coils, are arranged at an angle of 6° from each other, based on the central axis of the toroidal-type magnet. The cooling method used for the toroidal-type SMES is the conduction cooling type. When the cooling method for the toroidal-type SMES was designed, the two-stage Gifford–McMahon (GM) refrigerator was considered. The Bi-2223 HTS wire, which was made by soldering brass on both sides of the superconductor, is used for the magnet winding. Finally, the authors connected the toroidal-type SMES to a real-time digital simulator (RSCAD/RTDS) to simulate voltage sag compensation in a power utility.

The Technology of Fabrication & Application of Bi-2223 HTS Wires at InnoST

Comparing with the ordinary conducting wires, HTS wires have primary advantages of low loss and high current carrying capacity (as much as 100 times more than that of ordinary conducting wires). HTS wires, as a new type material, now are being widely applied to a great variety of areas. The R&D and fabrication of the Bi-2223 HTS wires at Innova Superconductor Technology Co., Ltd (InnoST) are introduced, including the main research results of cutting down the manufacture cost, improving the performance of the HTS wires and developing the diversified HTS wires. Meanwhile some HTS magnets and HTS current leads that we have produced over the past few years are introduced, such as 1.5 T Ag-sheathed Bi-2223 magnet and 15 kA HTS current lead, which is used in TOKAMAK system, and so on. The welding joint resistance of Bi-2223 wire is also studied.

Design of the Cryogenic System for a 400 kW Experimental HTS Synchronous Motor

A 400 kW radial-axial flux type experimental HTS synchronous motor is designed. There are twelve armature coils used HTS wires in the motor. They are accommodated in the cooling vessels made of FRP material, and twelve cooling vessels are enclosed in the vacuum vessel. In order to cool the HTS coils of the motor, a sub-cooled liquid nitrogen cryogenic system is presented. The operation temperature is below 70 K. This system consists of HTS coils cryostats, liquid nitrogen transfer-line, liquid nitrogen dewar and a cold box with liquid nitrogen pump, G-M cryorefrigerators and some control valves inside. In this paper, different kinds of the heat loads of the system including the AC loss, current lead, supporters and radiation are presented. Basis on the heat load and operating temperature, the main parameters and equipments of the system are determined.

Application possibilities with continuous YBCO loops made of HTS wire

In our previous experiments we have produced YBCO rings machined from bulks for superconducting applications. In this work we examine the arrangement of the continuous superconducting loop made of HTS wire for advanced applications. A Korean group of researchers led by Hee-Gyoun Lee produced 100% BSCCO loops from tape for the first time in 2006 [1]. In our solutions we use parallel and serial turns from perfect YBCO loops made from HTS wire. Production of multi-serial turns is not the same as the "wind and flip" [1] method. In our case the twisting of the YBCO wire along its longitudinal axis can be avoided. We check the quality of the perfect YBCO loops with the transformation of the DC magnetic field [2]. In the case of the AC application we describe a new arrangement of the self-limiting transformer with using these loops. This self-limiting transformer can be a voltage or current restricting system. The paper presents the results of our experiments and opens new advanced applications of perfect YBCO loops made of HTS wire focusing on the efficiency and importance of the Korean team in creating the perfect closed loop.

Design of a Probe for Strain Sensitivity Studies of Critical Current Densities in Superconducting Wires

The critical current density of brittle superconducting wires used in high field magnets is very sensitive to axial strain. An accurate measurement of this strain dependence at various magnetic fields and temperatures is critical for magnet design and operation. A number of methods and techniques have been used, which generally fall into either the monotonic axial loading or bending spring techniques. The design of a variable-temperature probe to perform strain sensitivity measurements in Helium of both LTS and HTS wires is herein described. The sample is wound and soldered onto a helical Walters' spring device, which is fixed at one end and subjected to a torque at the free end. Both Ti-6Al-4V and CuBe were used as materials for the Walters' spring. Two concentric copper tubes act dually as 2000 A current and 60 Nm torque carriers. The torque is generated via a worm-gear setup and transmitted to the sample through the inner tube and spring assembly.

Study on Quench Protection Method With Regards to Normal Transition Behavior for HTS Coil

This paper presents the quench detection method with using normal transition behavior for HTS coil. If the HTS coil starts to propagate a normal zone by an initial quench, it will be recovered the superconducting state or runaway thermally. These behaviors were mainly determined by variety parameters like the magnitude of a disturbance, HTS coil size, the structure of winding wire and cooling condition. However, the first step of detection or protection for coils should be started from detecting the presence of a non-recovering normal zone. This paper classifies the initial quench behaviors of HTS wires or coils as a model of 3-type tendencies, and suggests suitable detection techniques for each tendency with using the end-to-end voltage of coil. In additional, this method is able to detect a quench without a decisive criterion used at other quench detection methods. In order to confirm the validity of the method, we used the HTS sample coil wound with YBCO tapes. This paper presents these results and the quench protection properties with fabricated detection method.

A Study on the Non-Inductive Coils for Hybrid Fault Current Limiter Using Experiment and Numerical Analysis

A Hybrid fault current limiter (FCL) proposed by our group previously is composed of a superconducting coil, a fast switch and a bypass reactor. The superconducting coil wound with two kinds of HTS wire has zero impedance when normal current flows in the coil. However, different quench characteristics of the HTS wire generate magnetic flux in the coil when fault current flows in the coil. As a result, the fast switch was opened by the repulsive force applied to the aluminum plate above the coil. In previous studies, our group verified operating characteristics and feasibility of the fast switch. In this paper, comparison of pancake type and solenoid type non-inductive coil wound with two kinds of the HTS wire was performed by using short-circuit test and finite element method. From these results, short-circuit characteristic of a coil can be acquired and magnitude of the repulsive force and magnetic field can be analysed.

Current limiting characteristics of transformer type HTS superconducting fault current limiter with rewound structure

A transformer type SCFCL of HTS wire with rewound structure has a primary coil of BSCCO wire connected to a power system and has a secondary coil of also BSCCO wire short-circuited. Both HTS coils were wound co-axially with rewound structure to get longer wire, that is, larger resistance at the normal state. The rewound structure offers greater flexibility in the design of the inductance and resistance of the SCFCL. It was experimentally confirmed that the SCFCL gives an inductive limiting impedance for smaller fault current while the only secondary wire transits to normal state and for larger fault current, it can give a resistive component additively by the normal transition of the primary wire. The current limiting characteristics of the proposed SCFCL were discussed by experimental results. Excellent recovery characteristics, that is, the recovery under load operation and repetitive limiting operation were confirmed experimentally.

Thermal conductivity of 2G HTS wires for current lead applications

We have studied the thermal conductivity of several 2G HTS coated conductor wires produced by AMSC's RABiTSTM/MOD processes. The measurements employed a non-steady state method in which the sample is connected to a cold head on one end and a copper block on the other end. The heat capacity of the copper block is used to determine heat flow through the sample as the cold head slowly warms up. Measurements were done at temperatures ranging from 10 K to 130 K on 2G wires made with a Ni 5at%W substrate and different lamination architectures. The focus of the investigation was on the effects of lamina material type, thickness of the silver layer and alloyed silver. The data show that 2G wires can be 3 times less thermally conductive when compared to 1G BSCCO wires with a Ag-Au matrix, making them excellent candidates for use in current lead applications.

Quench detection method for 2G HTS wire

2G HTS conductors are increasingly used in various commercial applications and theirthermal and electrical stability is an important reliability factor. Detection and preventionof quenches in 2G wire-based cables and solenoids has proven to be a difficult engineeringtask. This is largely due to a very slow normal zone propagation in coated conductors thatleads to formation of localized hotspots while the rest of the conductor remains in thesuperconducting state. We propose an original method of quench and hotspot detection for2G wires and coils that is based upon local magnetic sensing and takes advantage of 2Gwire planar geometry. We demonstrate our technique experimentally and show that itssensitivity is superior to the known voltage detection scheme. A unique feature of themethod is its capability to remotely detect instant degradation of the wire criticalcurrent even before a normal zone is developed within the conductor. Variousmodifications of the method applicable to practical device configurations are discussed.

Design and test of current limiting modules using YBCO-coated conductors

Within the cooperation between American Superconductor Corporation (AMSC) andSiemens Corporate Technology we have investigated the fault current limiting performanceof YBCO-coated conductors (also called second-generation or 2G HTS wires) stabilizedwith stainless steel laminates. Design rules for the length and width of the wiredepending on utility grid requirements have been established. Bifilar coils have beenmanufactured and tested with a typical limitation period of 50 ms under stepwiseincreasing voltage loads to determine the maximum temperature the wires canwithstand without degradation. Coils have been assembled into limiter modulesdemonstrating uniform tripping of the individual coils and recovery within seconds. Atpresent this cooperation is proceeding within a joint project funded by the USDepartment of Energy (DOE) that encompasses the design, construction and testingof a 115 kV FCL for power transmission within a time frame of 4–5 years, andadditional partners. Besides AMSC and Siemens, Nexans contributes the highvoltage terminations and Los Alamos National Lab investigates the ac losses.Installation and testing are planned for a Southern California Edison substation. Themodule planned for the transmission voltage application consists of 63 horizontallyarranged coils connected in parallel and series to account for a rated current of 1.2 kArms and voltageof 31 kVrms plus margins. The rated voltage of the module is considerably lower than the line to groundvoltage in the 115 kV grid owing to our shunted limiter concept. The shunt reactorconnected in parallel to the module outside the cryostat allows for adjustment of thelimited current and reduces voltage drop across the module in case of a fault. Thefault current reduction ratio is 42% for our present design. A subscale modulecomprising six full-size coils has been assembled and tested recently to validate the coilperformance and coil winding technique. The module had a critical current of 425 ADC and a nominal power of 2.52 MV A at 77 K. A complete series of tests with applied voltage up to 8.4 kVrms, prospective short circuit current up to 26.6 kArms and variation of phase angle at initiation of the fault has been performed. After more than40 switching tests the critical current of the module remained unchanged, indicating thatno degradation of the wire occurred.

전도냉각형 고온초전도 Wire의 전류도입부에서의 열적 퀜치

The heat generation in the high-<TEX>$T_c$</TEX> superconducting (HTS) wire is related with the cost efficiency and safe factor of HTS devices. This paper deals with the thermal quench at the conduction-cooled joint between HTS wire and copper terminals. The 3-D numerical simulation of thermal distributions in part of the copper terminals was implemented and the premature quench at copper block was observed through the test. The results will be helpful to design the conduction-cooled HTS magnets.