Applications Of High Temperature Superconductors Research Articles

Development of lab scale sub-cooled liquid nitrogen facility for high temperature superconductor applications

The technological advances in high temperature superconductors (HTS) have led to its use in various high voltage and high current applications. HTS based devices have huge application prospect compared to low temperature superconductors (LTS) owing to their higher engineering current density, higher critical temperature (hence higher operating temperature) resulting in high power density and lower investment on cryogenics. Here we report the development of sub-cooled liquid nitrogen facility for cooling small scale HTS application with single phase liquid nitrogen under a temperature range of 64 K-77 K. We have sub-cooled liquid nitrogen inside commercially available 50 L Dewar by boiling nitrogen under reduced pressure. As a proof of principle, we have cooled a 1 meter long vacuum insulated flexible cryogenic transfer line to 70 K using sub-cooled nitrogen. This same facility can be used to efficiently cool future High Temperature Superconductor (HTS) based applications at a laboratory scale.

Electromagnetic launching technology and boron at Moon for Space

Gelecek yıllarda, ay yerinde keşfedildiğinde, aydan uzaya malzeme nakliyesi yeteneklerinin geliştirilmesi planlanmaktadır. Uzay araçlarının yakıt ikmali için gerekli oksijen gibi ay malların yörüngedeki depolara taşınaması sağlanacaktır. Genel olarak aydan malzeme nakliyesi söz konusu olduğunda EMFS (Elektromanyetik Fırlatma Sistemi) teknolojisinin, yakın gelecekteki üstünlükleri çok iyi açıklanabilir. EMFS’nin kimyasal fırlatma sistemine göre, yüksek kapasiteli taşıma, yüksek güvenlik ve çevresel sürdürülebilirlik ile düşük bakım maliyetleri ve yüksek verimlilik gibi çeşitli avantajları bulunmaktadır. Sunulan ön konseptin geliştirilmesi ve bu tür bir sistemle dağıtımının fizibilite ve net faydası ile ilgili, yüksek yük taşıma kapasitesine sahip oluşu EMFS’yi desteklemektedir. EMFS halen sürdürülen bir çalışmadır ve özellikle donanım geliştirme aşamasında dikkate alınması gereken birçok zorlukları bulunmaktadır. Bu çalışmada Yüksek Sıcaklık Süperiletken (HTSC) MgB2 gibi malzemeler, ana güç üretimi, veriyolu çalışması, endüktif enerji depolama, devre açma anahtarları, başlatıcı bobinler ve yükler dahil, birçok EMFS bileşenleri için yaygın olarak kullanılan uygulamalardır.

Solution of 3D magnetization problems for superconducting film stacks

A stack of coated conductors is a perspective configuration for various applications of high temperature superconductors. We present an efficient fast Fourier transform-based numerical method for magnetization problems for a stack of flat films of the same (arbitrary) shape and compare it with the recently proposed finite element methods. For stacks containing a large number of densely packed films an accurate solution can be obtained as a properly rescaled solution for a stack of only several films. For an infinite stack the problem simplifies and becomes similar to that for a single film.

Photovoltaic effect in cuprate superconductor (Bi, Pb)2Sr2Ca2Cu3O10+δ and Bi2Sr2CaCu2O8+δ under magnetic field

Photovoltaic effects of Bi-2223/Ag and Bi-2212/Ag heterostructures under magnetic fields up to ± 9 T induced by continuous purple-laser irradiation have been investigated in a wide temperature range between 10 K and 350 K. There is a broad peak in the temperature dependence of Voc for the Bi-2223/Ag system near 45 K which can be ascribed to the minority phase of Bi-2212 within the Bi-2223 sample. The anomalous magnetic field dependence of Voc below 60 K suggests that the low temperature magnetic behavior of Voc for the Bi-2223/Ag system is greatly affected by the minority phase Bi-2212. No polarity reversal of Voc was observed at the superconducting transition of Bi-2212/Ag heterostructure, consisting with that for SmO0.7F0.3FeAs/Ag system but opposite to that of Bi-2223/Ag and YBCO/Ag systems. This observation indicates that the majority charge carriers in this heavily over-doped Bi-2212 are electrons other than holes. Our results show that the photo-induced voltage has a photovoltaic nature closely related to the built-in electric field of the intrinsic metal/superconductor interface. The magnitude and the direction of the built-in electric field can be changed by applying an external magnetic field and/or varying the laser intensity. Our data provide a new dimension of information for depicting a more comprehensive picture of metal/HTSC heterostructure system and may lead to new applications of high temperature superconductor in the field of photo-electronic and magnetic sensing devices.

AC Loss Property of Stacked REBCO Superconducting Multifilamentary Tapes under Perpendicular Magnetic Field

For AC applications of high-temperature superconductors, such as REBa2Cu3Oy (REBCO, RE = rare earth) superconducting tapes, an AC loss is a great part of total heat load of cooling systems. In the case of conduction cooling, it may cause a serious temperature rise of the superconducting systems. Therefore, it is very important to reduce the AC loss in superconducting windings and grasp its properties under various conditions. For AC loss reduction, REBCO tapes should be scribed into a multifilamentary structure by the laser-scribing technique. In this study, AC loss properties in the non-scribed and scribed tapes were investigated, especially for Bm < Bp, where Bp is the breaking point of the AC loss curve and corresponds to the penetration field where the magnetic flux penetrates to the center of the tape or filaments. Further, the dependences of Bp on the number of stacking tapes and filaments were investigated from the viewpoint of demagnetization effect. It was cleared that the AC loss for Bm < Bp decrease and Bp increase with increasing number of stacked tapes.

Quench Characteristics Comparison Between Solid Nitrogen and Conduction Cooled REBCO Coil Under Thermal Disturbance and Over Current Pulse

In power system application of high temperature superconducting (HTS) equipment, large amount of heat caused by thermal disturbance or over current during sudden electric interruptions will endanger the thermal stability of HTS devices. However, solid nitrogen (SN2) with large heat capacity can enhance the thermal stability of HTS magnets. In this paper, the quench characteristics of SN2 and conduction cooled REBCO coil under thermal disturbance and over current pulse has been investigated at 60 K. For the thermal disturbance experiment, the minimum quench energy, longitudinal and transverse normal zone propagation velocities in SN2, and conduction cooled system are compared and discussed. The strain response property of the coil from quench to complete cooled down after power off during the quench process has also been preliminarily discussed. What is more, the accumulated peak voltage and strain of the coil during the over current pulse test has been studied. These results show that SN2 can help to enhance the thermal stability of REBCO coil under thermal disturbance and over current pulse.

Technology Collaboration Programme on High-Temperature Superconductivity (HTS): HTS A pplications and the Need for International Standardization Activity

Electric power systems' application of high-temperature superconductivity (HTS) is the main focus of the HTS Technology Collaboration Programme (TCP) of the International Energy Agency. Through its nine active contracting parties and two sponsors, the HTS TCP fosters the penetration of HTS applications in electric power grids. HTS TCP activities facilitate information exchange among the most important HTS actors worldwide. As a common platform to prompt HTS applications, the HTS TCP also paves the way for progress in international standardization. Information exchange within the HTS TCP is often the starting point for developing standards that influence present and future power systems design. Recent activities demonstrate the trend toward collaborative outcomes in standardization; examples include the liaisons between the International Electrotechnical Commission's (IEC's) Technical Committee on superconductivity (TC 90) and CIGRE; Project Team 63075, launched in the framework of the IEC's Technical Committee on electric cables (TC 20); and two round robin tests on MgB2 conductors.

Coated Superconducting Tape Model Based on the Distribution of Currents Between the Tape Layers: Computing Implementation

In large-scale applications of high-temperature superconductors (HTS) such as superconducting fault current limiters or superconducting magnetic energy storage, HTS tapes are often the simplest element involved in the design of such elements. In turn, those elements are part of wider environments, as power grids, which are analyzed by programs using models of well-known conventional electrical elements, e.g., resistances, reactors, transformers, switchgear, etc. The problem of superconducting elements to be modeled as the other ones is the nonlinearity of their response, due to the nonlinearity of the superconducting tape in which the elements are done. The proposal of this work is to develop a model of the coated superconducting tape based on parameters that adjust the nonlinearity of the tape under the hypothesis that: 1) the electrical current is distributed between the layers of the tape (mainly between the superconducting layer and the stabilizer) in a different way depending on the peak value; and 2) the hysteresis in the superconducting layer can be modeled as a function of the stationary V ( I ) characteristic. Experimental measurements have been done in order to adjust the parameters of the model, which have to be determined for each type of tape in the same way that the parameters of ferromagnetic cores have to be determined for each material. Several models have been implemented in a MATLAB environment and tested to be part of a more complex circuit. The best solution for straight tape and self-field was developed in Simulink, and results and conclusions are presented here.

Discharge Mechanisms in Liquid Nitrogen—Breakdown Field Strength of Gaseous Nitrogen

The application of high-temperature superconductors in medium- and high-voltage equipment requires an insulation system which prevents electric breakdown within the required working conditions. As dielectric insulation and coolant liquid nitrogen can be used, the design of the insulation requires knowledge of the dielectric behavior of liquid nitrogen. During normal operation, the insulation system usually does not generate vapor bubbles. But if fault or certain working conditions occur, vapor bubbles can occur. In this case, the dielectric behavior of gaseous nitrogen, close to the temperature of the liquid, becomes the discharge governing criterion. Furthermore, the discharge in liquid nitrogen has not been clearly explained. Therefore, this paper investigates the gas breakdown as a possible discharge process. To investigate if the discharge happens according to the gas breakdown, breakdown voltages of cryogenic and room temperature nitrogen gas are measured. This is done for uniform and nonuniform electric field at ambient pressure. Then the gas constant k, an integration of ionization coefficient over discharge path, is deduced from simulations and analytical formulas. These values of k yield a possible criterion to decide if a gas breakdown happens according to Townsend or Streamer theory. This offers new insights into the breakdown of liquid nitrogen.

Recent Status and Progress on HTS Cables for AC and DC Power Transmission in Korea

The direction of the development of large-scale electric power networks has very much coincided with the history of increasing voltage values ever since the advent of Joule heat loss. However, a high-temperature superconducting (HTS) technology has changed the direction of that history. Furthermore, the HTS technology will rapidly accelerate the speed of such change due to its extremely high current density with no Joule heat loss. For these reasons, many different types of HTS electric power transmission applications have been being discussed, and selected items have been developed. Within a few decades, the technology of HTS ac and dc power transmission applications had already been developed and close to the required level for industrialization. Moreover, some of these applications have been installed, energized, and are operating within real power networks. In this paper, we report on the current status and progress in HTS applications of ac and dc power transmission. In particular, this paper focuses on the application field of superconducting cable among various HTS power applications. In South Korea, the Korea Electric Power Corporation, Naju, aims to introduce more new technologies in order to develop the Korean power network, and it believes that an HTS is a key factor in the development of the next generation of power grid, which will be discussed in detail in this paper.

Fatigue Behavior of Critical Current Degradation for YBCO Tapes at 77 K

In the application of high-temperature superconducting (HTS) tapes, they are prone to subject fatigue loadings such as repeated thermal cycles, periodic electromagnetic force, and so on, which will affect the performance of superconductors and lead to the degradation of superconducting magnets and power systems. To optimize the design of a superconducting device, it is important to fully understand the fatigue properties of REBCO conductors. Recently, fatigue loading that influences critical current $(I_{{\text{c}}})$ of HTS materials has been studied by several research teams. However, the influence of mechanical fatigue stress on REBCO tapes under background magnetic field has not been reported. In this paper, the $I_{{\text{c}}}$ as a function of external magnetic field under different loading cycles was investigated at 77 K. The results showed that for fatigue damage of a YBCO-coated conductor, the influence of stress amplitude on $I_{{\text{c}}}$ degradation is more significant than the maximum stress applied to the coated conductor. Under higher fatigue load cycles, the YBCO-coated conductor was insensitive to the external magnetic field.

Dynamic levitation performance of Gd–Ba–Cu–O and Y–Ba–Cu–O bulk superconductors under a varying external magnetic field

We report that the dynamic levitation force of bulk high temperature superconductors (HTS) in motion attenuates when exposed to an inhomogeneous magnetic field. This phenomenon has significant potential implications for the long-term stability and running performance of HTS in maglev applications. In order to suppress the attenuation of the levitation force associated with fluctuations in magnetic field, we compare the dynamic levitation performance of single grain Y–Ba–Cu–O (YBCO) and Gd–Ba–Cu–O (GdBCO) bulk superconductors with relatively high critical current densities. A bespoke HTS maglev dynamic measurement system (SCML-03) incorporating a rotating circular permanent magnet guideway was employed to simulate the movement of HTS in a varying magnetic field at different frequencies (i.e. speed of rotation). The attenuation of the levitation force during dynamic operation, which is key parameter for effective maglev operation, has been evaluated experimentally. It is found that GdBCO bulk superconductors that exhibit superior levitation force properties are more able to resist the attenuation of levitation force compared with YBCO bulk materials under the same operating conditions. This investigation indicates clearly that GdBCO bulk superconductors can play an important role in suppressing attenuation of the levitation force, therefore improving the long-term levitation performance under dynamic operating conditions. This result is potentially significant in the design and application of HTS in maglev systems.

Dynamic Resistance Measurement of a Four-Tape YBCO Stack in a Perpendicular Magnetic Field

Dynamic resistance occurs when HTS (high-temperature superconductor) coated conductors carry dc current under ac magnetic field. This dissipative effect can play a critical role in many HTS applications. Here, we report on dynamic resistance measurements of a four-tape YBCO stack comprising 4-mm-wide coated conductors, which experience an applied ac perpendicular magnetic field with an amplitude of up to 100 mT. Each tape within the stack carries the same dc current. The magnetic field amplitude, the frequency of the magnetic field, and the dc current magnitude are varied to investigate the influence of these parameters on the dynamic resistance. We find that the threshold field of the stack is significantly larger than that of a single tape when dc current is small, which we attribute to coherent shielding effects from circulating currents present in each wire in the stack.

Superconducting magnetic bearings with bulks and 2G HTS stacks: comparison between simulations using H and A-V formulations with measurements

A-V and H are two of the most widespread formulations applied in the literature to calculate current distribution in high-temperature superconductors (HTSs). Both formulations can successfully solve problems related to large-scale HTS applications, but the way to implement the calculations is different. In recent years, several authors have chosen the H formulation to solve problems related to HTS applications. This choice can probably be attributed to the easy implementation of the H formulation with the aid of commercial finite element method (FEM) software, producing precise results and performing fast calculations. In a previous work, we proposed the use of the H formulation to solve superconducting magnetic bearing (SMB) problems. However, most of the SMB simulations presented in the literature are solved using the A-V formulation implemented with the finite difference method (FDM). Which of these two techniques is more suitable for superconducting magnetic bearing applications? This paper aims to answer this question. In order to do so, an experimental rig was developed to test SMBs using YBCO bulks or stacks of coated conductors. The simulated levitation force results from the A-V formulation using FDM and from the H formulation using FEM were compared with the experimental data. In general, the calculation time and the results error obtained with both formulations are comparable. It is worth mentioning that the main contribution of this paper is to present improvements to reduce the A-V formulation computational time and details of how to implement it using FDM in any platform. For this reason, most of this work is about the A-V formulation, while the H formulation is just presented for comparison.

The effect of condensation area and operating temperature on heat transfer capacity of a closed loop thermosyphon cooling system for HTS machinery

A sophisticated cooling system is necessary for applications of high-temperature superconductor (HTS) for electric devices. Among them, status of rotating machine requests to maintain the temperature of HTS field poles under 40 K. We have employed a thermosyphon (TS) as cooling system for HTS rotating machines. The TS cooling is based on natural convection of coolant and does not require a forced circulation. Advantages of the TS cooling system are simple, light weight mechanical composition and high heat transfer coefficient with latent heat. The operating temperature of the TS cooling system depends on the saturation temperature and the pressure of coolant. Thus, the saturation pressure of the TS affects the performance of the TS cooling system. In this paper, we investigate the relationship between the saturation pressure and the condenser heat transfer area. We studied a heat transfer capacity under the heat load with different neon quantities using the TS cooling system. The saturation pressure increases with the heat load and/or condenser temperature increment. Reducing the number of condensers i.e. decrease of condensation area, the saturation pressure increases and the heat transfer capacity decreases. This result shows that the saturation pressure is proportional to the temperature difference between condenser temperature and the saturation temperature calculated by saturation pressure.

The Dielectric Strength of Nomex 410 Paper in Liquid Nitrogen Under Boiling Situations

It is crucial for the successful application of high-temperature superconducting (HTS) power transformers that they are able to survive under abnormal operations, such as a short-circuit fault. Modeling, based on the design of a four-winding three-phase HTS power transformer, suggests severe boiling will occur on the surface of the winding during a short-circuit fault and will jeopardize the turn-to-turn insulation of the HTS power transformer. In this paper, a turn-to-turn insulation breakdown experiment platform involving the introduction of boiling on the surface of electrode has been built. Nomex 410 paper, one of the candidates for turn-to-turn insulation in the design of the HTS power transformer, was tested. The characteristics of dielectric strength of Nomex 410 in three different thicknesses (0.13, 0.18, and 0.25 mm) have been investigated, without boiling, as well as under different boiling situations, in an open bath of liquid nitrogen. The voltage application methods applied during both experiments test the electrical breakdown of Nomex 410 under a dynamic situation. The experiment results show that when under film boiling, compared to the test results for nucleate boiling, the dielectric strength of Nomex 410 paper decreases by approximately 38% of the value when no boiling is involved. Moreover, it is verified that the presence of an electric field accelerates the heat transfer between the liquid nitrogen and the heated electrode.

Magnetic Field Angular Dependence of Magnetization Loss in ReBCO Superconducting Tapes

In the applications of high-temperature superconductors (HTS), the HTS tapes are usually exposed to the external magnetic field with different orientations. The critical current and AC loss are affected by both the field amplitude and field angles due to the anisotropy of HTS tapes. In this work, we first introduce the experimental system to measure the magnetization loss in HTS tapes based on the calibration-free method. Then, we present the magnetization loss results in 4.8-mm-wide AMSC wire, 4-mm-wide SuperPower wire, 4-mm-wide SuNam wire, and 10-mm-wide Fujikura wire in a perpendicular applied field at 77 K. The field amplitude is up to 100 mT, and the frequency varies from 44.2 to 87.1 Hz. We also present the magnetization loss in AMSC wire, SuperPower wire, SuNam wire, and Fujikura wire at different field angles. The field angle varies from 10 to 90 ∘ in 10 ∘ steps. The loss reduction with the decreasing of the field angle shows the anisotropic property of HTS tapes. We finally plot the measured magnetization loss of the samples as a function of the magnetic field amplitude normalized by the field angle to verify an empirical formula.

Numerical Simulations of AC Losses in Multifilamentary Superconducting Tapes Under Bending Strain

AC loss has become a key problem for practical applications of high-temperature superconductors. It is well known that mechanical deformation will affect the critical current and ac loss as the superconductor is subjected to the magnetic field or transport current. In this paper, the ac losses in Bi2Cr2Ca2Cu 3O10 (Bi2223)/Ag tapes under bending deformation are investigated. Bi2223 tape consists of Ag matrix and Bi2223 filaments, and the ac losses are generated by transport current and external field. By considering the plastic deformation of Ag matrix and residual strain, the simplified mechanical fracture model is established. Then, the finite element method analysis is used to investigate the relation of critical current and ac loss with bending deformations, and the losses are presented for different transport current and external magnetic field conditions. The influences of filament fracture on the ac loss are discussed for transport current and external magnetic field cases, respectively.

Fast Algorithm for Evaluating Critical Current of High-Temperature Superconducting Pancake Coil

Second-generation (2G) high-temperature superconducting (HTS) tapes are now capable of carrying very high transport current and promising for a wide range of applications. The critical current of HTS coils is important for applications, such as superconducting electric machines, superconducting magnetic energy storage, and superconducting magnets. Therefore, precisely and quickly calculating critical current of HTS coils is very important for designing HTS devices. This paper provides a fast algorithm for evaluating critical current of HTS pancake coil. The fast algorithm is realized through a stationary model, which is based on finite element method (FEM) software. The stationary model means that the model is solved by stationary study instead of time-dependent study. To validate this method, a pancake HTS coil was wound and its critical current was measured. Meanwhile, an axial symmetric stationary model was built according to the geometry of the measured HTS coil. By comparing measured and calculated results, the effectiveness of the stationary model was demonstrated. Moreover, the stationary model is compared with H formulation model. The calculated results by the two models are nearly the same. However, by using stationary calculation, the stationary model can remarkably speed up the computational process. Due to the advantage of calculating speed, the stationary model can be used to characterize and design large-scale HTS applications.

Low resistance splices for HTS devices and applications

This paper discusses the preparation methodology and performance evaluation of low resistance splices made of the second generation (2G) high-temperature superconductor (HTS). These splices are required in a broad spectrum of HTS devices including a large aperture, high-field solenoid built in the laboratory to demonstrate a superconducting magnetic energy storage (SMES) device. Several pancake coils are assembled in the form of a nested solenoid, and each coil requires a hundred meters or more of 2G (RE)BCO tape. However, commercial availability of this superconductor with a very uniform physical properties is currently limited to shorter piece lengths. This necessitates us having splices to inter-connect the tape pieces within a pancake coil, between adjacent pancake coils, and to attach HTS current leads to the magnet assembly. As a part of the optimization and qualification of splicing process, a systematic study was undertaken to analyze the electrical performance of splices in two different configurations suitable for this magnet assembly: lap joint and spiral joint. The electrical performance is quantified in terms of the resistance of splices estimated from the current-voltage characteristics. It has been demonstrated that a careful application of this splicing technique can generate lap joints with resistance less than 1nΩ at 77K.