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Sandwiched paper for dielectric capacitors exhibited superior energy densities and high efficiencies under high voltages over a broad temperature range. [Display omitted] • Scalable fabrication of sandwiched GF in ANF paper for dielectric capacitors. • Excellent dielectric energy storage under high voltage over broad temperature range. • Sandwiched AGA5 paper exhibited ultrahigh breakdown strength at elevated temperatures. • Dielectric papers showed a record high U d of 11.7 J·cm−3 at 200 °C under 400 MV·m−1. High-performance capacitive energy storage under high voltages over a broad temperature range is eminently indispensable for the next generation of microelectronics and electrical power modules. The available dielectric polymer nanocomposites, unfortunately, are confined to the relatively low-temperature regimes (usually below 200 °C) and that hinders their practical applications. This work presents the scalable fabrication of highly thermostable phosphorous crosslinked aramid nanofiber (PANF) paper with a sandwiched layer of high aspect-ratio electrically insulating graphene fluoride (GF) nanosheets prepared by ultrasonic spraying. The sandwiched layer remarkably diminishes the conduction current density and dielectric loss, thereby imparting the ANF paper exceptional breakdown strength and much-enhanced energy density at elevated temperatures. Owing to the excellent combination of ultrahigh breakdown strength and large displacement (∼0.076 C·m−2 under 502 MV·m−1), the sandwich-structured AGA (PANF-GF-PANF) dielectric paper shows the maximal discharged energy density of 16.7 J·cm−3 with a charge–discharge efficiency of 86% at 30 °C and a record-high discharged energy density of 11.7 J·cm−3 with a charge–discharge efficiency of 87.2% under an applied electric field of 400 MV·m−1 at 200 °C. In addition, the flexible sandwich paper shows outstanding stability up to 500 °C. This work opens up new possibilities for the mass production of flexible high-temperature dielectrics for capacitive energy devices operating in harsh environments. [ABSTRACT FROM AUTHOR]

The electrical insulation design of high voltage superconducting fault current limiters (SFCLs) should be confirmed for the stabilization of the power grid. This paper describes numerical analysis for high voltage SFCLs based upon the AC and lightning impulse dielectric tests. To calculate the field utilization factor, the electric field distributions for numerical analysis were calculated by finite element method (FEM) simulation tool. The correlation of experiments results and the field utilization factor was investigated. From the results, the electric field criterion of liquid nitrogen at 200 kPa was calculated. Furthermore, safety factor was also considered to design single-phase 154 kV class SFCL. This insulation design in liquid nitrogen focused only two parts of SFCL. Part 1 is gap distance between a cryostat and superconducting coils. Part 2 is gap distance between series-connections of non-inductively wound solenoid type coils. [ABSTRACT FROM PUBLISHER]

Sub-cooled liquid nitrogen (LN2) condition is a very useful method to increase the current rating capacity of YBCO tapes. Thus, the lightning impulse dielectric characteristics of sub-cooled LN2 condition should be investigated for designing high voltage superconducting machines. The sphere-plane electrode systems were used to simulate the internal structure of high voltage superconducting machines such as superconducting fault current limiters. The lightning impulse dielectric tests on saturated and sub-cooled LN2 condition were carried out by using the sphere-plane electrode systems. In addition, a quasi-uniform electric field distribution between the sphere-plane electrodes was calculated by the finite element method (FEM) simulation tool. The field utilization factor was calculated by the FEM simulation results. The lightning impulse breakdown voltage of various geometrical configurations between the sphere-plane electrodes in sub-cooled LN2 conditions was compared with that of in saturated LN2 condition. Finally, the lightning impulse breakdown voltage with 50% probability and its relations with the utilization factor have been described in this paper. [ABSTRACT FROM AUTHOR]

It has been widely established that gaseous helium (GHe) can be injected into a sub-cooled liquid nitrogen (LN2) cooling system to control the pressure of such a system because of its non-condensing characteristics. A sub-cooled LN2 cooling system is known as one of the most promising method to develop a large scale superconducting machine refid="ref1"/. Unfortunately, the electrical breakdown voltage of GHe is not good enough for developing a high voltage electric machine such as a superconducting fault current limiter (SFCL). To enhance the dielectric characteristics of current leads placed in GHe, the use of solid barriers is regarded as an efficient method. In this study, experiments are made on the dielectric characteristics of GHe and the barrier effects and results are analyzed in order to improve the dielectric performance of a high voltage SFCL using a sub-cooled LN2 cooling system. The dielectric experiments of the energized sphere and the grounded plane in GHe are examined according to various pressures with a solid insulating barrier. The dielectric experiments are performed by installing barriers made of glass fiber reinforced plastics (GFRP) between two electrodes and the electrical breakdown voltage according to the pressure of GHe and the position of a barrier is observed. As a result, it is found that the position of a solid barrier and the pressure of GHe are important in enhancing the dielectric characteristics of a sphere-to-plane electrode system with quasi-uniform field. [ABSTRACT FROM AUTHOR]

A sub-cooled liquid nitrogen (LN2) cooling system is known as an appropriate method for developing a high voltage superconducting fault current limiter (SFCL). The pressure of a sub-cooled LN2 cooling system should be controlled by injecting non-condensable gas such as gaseous helium (GHe) and gaseous neon (GNe) into the cryostat. Therefore, the electrical breakdown voltage of current leads is directly influenced by an injected gaseous medium. In this study, electrical insulation experiments on GHe and GNe are conducted and the results are compared with each other. Also, the dielectric characteristics of GHe and GNe are analyzed by using field utilization factors. It is found that the dielectric characteristics of GHe are superior to those of GNe under the same conditions. The experimental results are applicable for designing the current leads of a high voltage superconducting fault current limiter. [ABSTRACT FROM AUTHOR]

Abstract: In the present study, a novel solenoid type bifilar coil is proposed for high-T c superconducting fault current limiter (SFCL) which is composed of two windings in a bobbin and their winding directions are opposite with each other to have non-inductive characteristics. The two windings are connected in parallel at the current terminals for large current capacity. Besides, the current terminals are at the ends of the coil so that the electrical insulation design may be easier than that of other non-inductive coils. The novel solenoid type bifilar coil for SFCL is fabricated with BSCCO 2223 and tested in LN2 bath at 77K to investigate the current and voltage sharing as well as the current limiting effects. According to the test results, the current is limited effectively at first peak after the fault and the current sharing performance in each winding is verified under the normal and fault conditions. In order to compare with other bifilar coils, the AC losses are measured. [Copyright &y& Elsevier]

Abstract: With the successful commercialization of Bi-2223 powder-in-tube wire, various attempts in the R&D of the high-T c superconducting (HTS) magnets for high magnetic field applications are being implemented actively. Operating temperature of HTS magnet has to be maintained at the designed level but the magnetic energy and mechanical disturbance can cause unstable operational temperature of HTS magnet. Especially, the generated heat energy of inner HTS winding is apt to be accumulated, so the normal region appears in HTS winding. This paper deals with the quenching characteristics of three kinds of selected Bi-2223 wires: the high current density wire (HC-A) and the high strength wire (HS-A) made by AMSC and HTS wire (HW-I) made by Innost. The Innost wire has the highest minimum quench energy (MQE). The high current density wire has the highest normal zone propagation velocity (NZPV). [Copyright &y& Elsevier]

To develop a High-Tc superconducting (HTS) magnet that is applicable to the high voltage electric device applications, it is necessary to consider several important factors such as large critical current, reliable electric insulation system, stable cryogenic status, expected economic benefits, and so on. This paper deals with the skills to design and manufacture the high voltage HTS DC magnet accepting large pulse input current. The multi-stacked HTS solenoid winding was suggested for the HTS magnet having large critical current. To protect the HTS winding, when quenched, the copper layer was suggested as a buffer sharing the large pulse current. The thin grooves on the GFRP bobbins not only guide the HTS winding but also play the role of electrical insulation for the high voltage application. With regard to the thermal stability of the magnet, sub-cooled liquid nitrogen cooling system was used for the cooling system of the HTS DC magnet. To reduce the resistance of the normal conducting parts in the HTS magnet, several HTS tapes were additionally attached on these parts. Based on this study, the HTS DC magnet for the 2.3 MVA class high-Tc superconducting fault current limiter (HTSFCL) was successfully manufactured and tested. The HTS DC magnet developed by this study endured 2.53 MJ (18.66 MWmax) without any evidence of quench. [ABSTRACT FROM AUTHOR]

Abstract: The 21st Century Frontier R&D Program was planned to develop and commercialize the inductive Superconducting Fault Current Limiter (SFCL) in Korea until 2011. The 1.2kV/80A inductive SFCL was planned to develop at the first year in the first phase (2001–2002) and the 6.6kV/200A inductive SFCL for short run operation test was planned to develop at the second and third year in the first phase (2002–2004). The experimental characteristics of conduction-cooled cooling system developed in the first year was very weak from the sudden large thermal disturbance. Therefore, the conduction-cooled cooling system was concluded not appropriate for the cryogenic technology of the application of superconducting fault current limiter. In the third year research, the improved sub-cooled nitrogen cooling system was adopted and investigated. In this paper, the characteristics of each cooling type was compared and the basic deign of ameliorated cooling system was introduced and the total heat load of the cooling system was calculated and compared with the heat load of the cooling system developed at 2nd year research. [Copyright &y& Elsevier]

The conduction-cooled cryogenic cooling system for 1.2 kV/80 A inductive Superconducting Fault Current Limiter (SFCL) was fabricated and tested for its cooling characteristics in 2002. The observed thermal stability of the conduction-cooled system was very unreliable and precarious for the applied superconducting equipment with very large variation of currents like SFCL. Therefore, we replaced the conduction-cooled system with the sub-cooled nitrogen system for the 6.6 kV/200 A SFCL. In this paper, the design techniques and test results of cooling characteristics were introduced. The conditions for achieving the sub-cooled nitrogen state were 1 atm and 64 K. First, the temperature of 64 K was achieved by using the rotary pump and then the pressure of 1 atm was achieved by GHe. The characteristics of liquid nitrogen were strongly enhanced in these conditions. This fabricated cryogenic system merely for the short run operation test SFCL. Finally, the cryogenic system for the long run operation test SFCL was introduced. [ABSTRACT FROM AUTHOR]

As a part of the 21st Century Frontier R&D Program in Korea being performed from 2001, a DC Reactor type Superconducting Fault Current Limiter (SFCL) is being developed. The target of the first phase is to develop a 6.6 kV/200 A class 3-phase SFCL as a prototype for a 154 kV class. This prototype SFCL has a magnet wound with a high-Tc superconducting wire (Bi-2223) operating at 65 K. The magnet uses solenoid bobbins with grooves for the tape wire. Its inductance is about 84 mH. An AC-DC power converter was made with Light Trigger Thyristor (LTT) having a phase controller. The maximum voltage is 7 kV. The DC reactor, which is cooled by sub-cooled nitrogen, uses a three phase transformer with dual tap for series connection with a power line. Through several experiments this SFCL shows current limiting performance about 50% of short circuit current at short run tests. [ABSTRACT FROM AUTHOR]

An inductive superconducting fault current limiter protects power system by limiting the amplitude of fault current by the inductance of its dc reactor. Therefore, it is very important to design the dc reactor of high critical current prior to fabrication. At first, the optimal design parameters were calculated by using finite element method and then the superconducting dc reactor for 1.2 kV/80 Arms inductive superconducting fault current limiter was designed by considering the conduction-cooling characteristics. Moreover, the design, fabrication and conduction-cooling method of the superconducting dc reactor were introduced. Actually, the superconducting dc reactor was fabricated and cooled down to 20 K by using GM cryocooler. Finally, the short-circuit test was performed and the experimental results were discussed. [Copyright &y& Elsevier]

High-voltage superconducting apparatuses, such as superconducting fault current limiters, superconducting transformers, and superconducting cables, are operated in high voltage, cryogenic conditions. A superconducting coil system may breakdown electrically not only in quench state but also in normal state (Kang et al. IEEE Trans. Appl. Supercond., 17, 1493-1496, ). In this paper, dielectric experiments of liquid nitrogen according to electrode material are performed with AC and lightning impulse voltages to design an electrically reliable, high voltage superconducting system. The electrical breakdown voltage of liquid nitrogen for various pressures (from 0.1 MPa to 0.4 MPa) strongly depended on the electrode material. Therefore, the design of a high-voltage superconducting apparatus should consider the kind of electrode material. The experimental results in this study can be used to design the different parts of a high-voltage superconducting apparatus according to the electrode material. [ABSTRACT FROM AUTHOR]

Study of the dielectric characteristics on gaseous insulation media is important for designing and developing current leads of superconducting machines with a sub-cooled N2 cooling method. In the case of using a sub-cooled N2 cooling method, a gaseous insulation medium, such as He, Ne, SF6, CF4, or N2, should be injected to control the pressure and enhance the dielectric performance of current leads simultaneously. In this study, dielectric experiments on various gaseous insulation media are conducted and experimental results are analysed by considering field utilization factors. In addition, the functional equations are derived from experimental results and computational analyses. It is found that the dielectric characteristics of gaseous insulation media are determined by the maximum electric field intensity at sparkover voltage. This denotes that the electrical breakdown voltage of insulation gas could be estimated using deduced functional equations. Finally, the conceptual electrical insulation designs of current leads for a superconducting apparatus according to various insulation media are presented and the results are compared. The results may be applied to develop and commercialize a high voltage superconducting apparatus using a sub-cooled N2 cooling method. [ABSTRACT FROM PUBLISHER]

A high-Tc superconducting (HTS) DC reactor has been developed as a part of DC reactor type superconducting fault current limiter (SFCL) rated on 6.6 kV/200 A. The DC reactor was a solenoid coil and was wound with a 4-parallel stacked tape. This coil has 5 layers which are connected in series each other. The inductance of the coil is about 84 mH. This paper deals with the design, fabrication and testing of the DC reactor. For this design of the coil, a prototype solenoid coil had been used. Using the experimental result of a prototype solenoid, the number of stacks and the inductance were designed. The winding machine for the HTS solenoid was manufactured. Using this machine, the large-scale HTS solenoid using a Bi-2223 tape was fabricated successfully. Characteristics of the fabricated coil were observed through a measurement of voltage as current transportation. [ABSTRACT FROM AUTHOR]

The High Temperature Superconducting (HTS) electric equipment using Bi-2223 wire successfully commercialized 1st generation HTS wire, has been developing by many research groups. HTS coil is one of the most important parts in HTS electric equipment. To enlarge the critical current, the operating temperature of the equipment tends to go down and number of HTS wire tends to increase. Thus, it is very important to determine the whole critical current of HTS coil for the stable operation of HTS equipment. The whole critical current of multi-stacked wire of HTS solenoid coil is not equal to the sum of the critical current of each stacked wire because of nonuniform current sharing occurs in multi-stacked HTS wires and each HTS path does not has the same critical current. In this paper, current sharing in two types of 5-stacked HTS solenoid coils, made up of 1 copper layer which is a current buffer layer of HTS coil and 4 HTS wire layers, was analyzed. One was wound with Bi-2223 wire insulated with polyimide tape and the other was wound with noninsulated Bi-2223 wire. All of the Bi-2223 wires were reinforced with stainless steel. The simulation results of current sharing in multi-stacked HTS coils coincided well with the experimental results. Based on these results, the current sharing ratio of large scale HTS coil was also expected. The copper layer acted as a good current path when all the HTS wires were quenched. [ABSTRACT FROM AUTHOR]

Considering the deterioration characteristics of 2G hightemperature superconducting (HTS) tapes is necessary to design a mechanically and electrically robust superconducting coil. In this study, the deterioration characteristics of 2G HTS tapes such as the critical current ( I ) and n value are determined according to the electrical breakdown applied. AC, DC, and lightning impulse (IMP) voltages are applied to 2G HTS tapes stabilized by various materials to verify their deterioration characteristics. It is found that the degree of deterioration is dependent on the applied voltage and the type of 2G HTS tape. This implies that the deterioration characteristics of the 2G HTS tape by the discharge is influenced by the total energy of the input voltages whereas the variation in deterioration according to the type of the 2G HTS tape is a result of the electrical resistivity and hardness of the stabilizer material. Deterioration characteristics of 2G HTS tapes damaged by discharge voltages are analyzed by using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). [ABSTRACT FROM AUTHOR]

A high-temperature superconducting (HTS) coil system often operates in an environment cooled with liquid nitrogen (LN). However, it could be surrounded in part by gaseous nitrogen (GN) as a result of film boiling due to thermal quenching. This may negatively affect the dielectric reliability in a composite dielectric system relative to that of a liquid dielectric system because the intensity of the electric field increases at the gaseous dielectric layer. The increase in the electric field intensity with the gaseous dielectric layer may degrade the dielectric reliability of the HTS coil system. This study investigates the dielectric characteristics of a composite insulation system with GN and LN to design an HTS coil system with high reliability in a quench state. The dielectric experiments use a sphere-to-plane electrode system made of copper, and three types of voltages (AC, DC, and lightning impulse) are applied to the sphere electrode with a grounded plane electrode. The electrical breakdown voltage of the composite dielectric system is measured and analyzed with respect to the height of the gaseous nitrogen layer. Finally, the dielectric characteristics of the composite dielectric system corresponding to a given height of the gaseous nitrogen layer are compared with those of GN and LN dielectric systems. [ABSTRACT FROM AUTHOR]

Several types of solid insulation materials can be used as formers and insulators to develop high voltage superconducting coil systems. Solid insulation materials for a cryogenic environment are necessary to obtain excellent dielectric characteristics and robust mechanical characteristics. In this paper, partial discharge inception and the electrical breakdown characteristics of solid insulation materials are studied in LN under AC and DC voltages. Each of the experiments on solid insulation materials, such as glass fiber reinforced plastic and Bakelite, is performed for different thicknesses and stackings. The relationship between the discharge characteristics and the intensity of the electric field of the solid insulation materials can be calculated using the finite element method and can also be analyzed. Results show that the discharge characteristics of the solid insulation materials can be affected by the thickness and number of stacking sheets. In addition, the pattern of the partial discharge inception voltage under a DC voltage is not equal to that under an AC voltage. [ABSTRACT FROM AUTHOR]

Gaseous nitrogen (GN ) is used as an insulation and pressurization material for developing a high-voltage superconducting magnet system utilizing liquid nitrogen (LN ) cooling. In a LN cooling system, current leads for a high-voltage superconducting magnet are exposed to GN to temperatures that can range from 65 to 300 K. Therefore, a study on the electrical breakdown and partial discharge inception voltage test was performed considering the temperature and pressure variation of GN . The dielectric characteristics of GN were observed to improve as the temperature and pressure increased. In addition, the partial discharge inception voltage was similar to the behavior of dielectric breakdown voltage with respect to temperature and pressure. To confirm a functional relationship between the breakdown voltage and effect of the electrode surface area, experimental results were summarized using a field utilization factor. The dielectric breakdown voltage was found dependent on the field utilization factor. Consequently, the dielectric breakdown voltage of GN could be expressed as a function of field utilization factor according to temperature and pressure. [ABSTRACT FROM AUTHOR]

Recently super high-speed magnetic levitation (MAGLEV) using high-temperature superconducting (HTS) magnet has been expected as next-generation transportation since superconducting magnet can keep mighty levitation force. The superconducting magnet at MAGLEV train should be continually charged with high power in order to keep stronger and stable levitation force. Practically, since conventional power supply unit should be attached to HTS magnet in the MAGLEV, a large thermal loss is indispensably caused by power transfer wires and joints, those have been one of essential obstacles in the superconducting MAGLEV train. As the wireless power transfer (WPT) technology based on strongly resonance-coupled method realizes large power charging without any wires through the air, there are advantages compared with the wired counterparts, such as convenient, safety, and fearless transmission of power. From this reason, the WPT systems have started to be applied to the wireless charging for various power applications, such as transportations (train, underwater ship, electric vehicle). However, it has obstacles to commercialize, such as delivery distance and efficiency. To solve the problems, authors proposed the technical fusion using HTS resonance coil in the WPT system since the superconducting wire has merits a larger current density and higher Q -value than normal conducting wire. In this study, authors described the conceptual design of HTS receiver (Rx) coil with multi-copper antenna (Tx) coils. The priority characteristics of moving HTS receivers under multi-copper Tx coils are compared with and various copper Rx coils with radio frequency power of 370 kHz below 300 W. [ABSTRACT FROM PUBLISHER]

Layered crystal structures of various materials form through strong in-plane covalent and weaker out-of-plane bonding. The different bonding states can lead to the appearance of anisotropies not only of electronic/electrical and magnetic properties but also of structural disorder. A deeper understanding of the disorder anisotropy is essential to carry out structural modification and to enhance the material properties. However, in the case of multi-band MgB 2 superconducting materials that have layered structures, including graphene-like and six-membered rings, the nature and extent of the disorder anisotropy are not well understood. Also unknown is the influence on the transport critical current performance under magnetic fields in terms of charge-carrier scattering and vortex pinning. Herein, we have investigated the disorder anisotropy to reveal the relation with the in-field superconductivity. The MgB 2 phase formed by appropriate sintering conditions with carbon doping for high transport critical current performance exhibited a small anisotropy in the strain distribution and a large anisotropy in the crystallite size. The anisotropic behavior reflects small out-of-plane domains of crystallites with the strain distribution. The disordered formation may be the reason why the π band is usually dirtier than the σ band. In contrast, although the strain distribution in the in-plane structural state can be selectively tuned by carbon doping, the in-plane crystal growth is still considerably large. Such in-plane crystallization has shortcomings in terms of scattering and pinning. We therefore argue that further selective modification of the disordered structure, especially for the in-plane size properties, is a practical approach to achieve enhancement beyond the currently attainable transport performance. • The MgB 2 superconductor has a layered structure, with dimensionally different and weakly interacting multiple bands. • By tuning the charge-carrier scattering for the bands, MgB 2 still has room to further improve the electrical properties. • We elucidated the in-plane and out-of-plane disordered structures with the anisotropy in high-performance MgB 2 materials. • The in-plane mean periodic distance was much larger than the in-plane superconducting coherence lengths in clean samples. [ABSTRACT FROM AUTHOR]

A subcooled liquid nitrogen cooling system is known as the most promising method for developing a high-voltage superconducting apparatus, such as a superconducting fault current limiter, a superconducting transformer, and so on (Kang et al, IEEE Trans. Appl. Supercond. 18, (2), 628-631 2008). Gaseous nitrogen is injected into a superconducting magnet system to control the pressure and enhance the dielectric characteristics of a subcooled liquid nitrogen cooling system. In this case, the application of a solid insulating barrier between electrodes is regarded as an effective method to enhance the insufficient dielectric characteristics of gaseous nitrogen to develop a transmission superconducting apparatus. Dielectric experiments for a solid insulating barrier made of glass fiber-reinforced plastics (GFRP) in gaseous nitrogen are conducted under various pressures (0.1 ∼ 0.4 MPa), and the results are analyzed. A solid insulating barrier is installed between a rod to plane electrode system. The AC electrical breakdown characteristics according to the pressure of gaseous nitrogen and the position of a barrier between two electrodes are observed. [ABSTRACT FROM AUTHOR]

The linear accelerator, RAON, has been being developed as a part of the Rare Isotope Science Project (RISP) at Institute for Basic Science (IBS) in the Republic of Korea. In this paper, it is dealt with the design of a low T superconducting magnet system for an electron cyclotron resonance (ECR) ion source to utilize a 28-GHz radio frequency source. The superconducting magnet system for a 28-GHz ECR ion source consists of four solenoid coils and six saddle coils (a sextupole coil) (Taylor et al. IEEE Trans. Appl. Supercond. 10, 224-227, 2000). The detail specifications of each superconducting coil are designed by analyzing magnetic field to enhance the efficiency of beam extraction and electromagnetic force to improve the mechanical stability of a superconducting coil by using finite elements method (FEM) simulation. The definitive design parameters for manufacturing the superconducting magnet system for a 28-GHz ECR ion source of RAON accelerator are suggested considering electromagnetic characteristics. [ABSTRACT FROM AUTHOR]

Several types of solid materials are used in the development of high voltage superconducting magnet systems as the former and insulation barrier. The solid insulation materials used in cryogenic applications require excellent dielectric characteristics as well as robust mechanical characteristics. In this study, the dielectric experiments for three types of solid insulation materials, including glass fiber reinforced plastic (GFRP), epoxy (Stycast 2850FTJ), and Bakelite in liquid nitrogen (\LN2) at 77 K temperature are performed. Each experiment on the solid insulation materials is performed according to the type of applied voltage (lightning impulse and ac voltage) and the system pressure (0.1 \sim 0.4 MPa). Also, experiments considering the stacking effect of insulation sheets are performed. All electrical breakdown voltages are observed when the solid insulation materials are fully penetrated. Electrical breakdown experiments on GFRP and Bakelite sheets according to the number of stacking are performed and the results are compared. The relationship between the dielectric characteristics of solid insulation materials and the distribution of electric field intensity is calculated and analyzed by the finite elements method (FEM). The results revealed that the dielectric characteristics of solid insulation materials in \LN2 are directly affected by the distribution of electric field intensity and the number of stacking sheets. [ABSTRACT FROM PUBLISHER]

The magnetization loss of MgB wire was investigated using numerical calculations based on the finite element method. Various superconducting properties of MgB wire such as nonlinearity and the field dependence of the critical current were considered in the numerical formulation. An analysis of magnetization loss was carried out as a function of the external magnetic field for a wide range of operating temperatures. The numerical results were compared with conventional theories and were found to be in relatively good agreement. An alternate approach based on a normalization method using critical current data was also employed as a simple method for predicting magnetization loss. The effectiveness of the simple equation for predicting loss was verified by comparisons of both values for various temperatures. [ABSTRACT FROM AUTHOR]

Currently, studies on the development of high voltage superconducting machines are being conducted actively in many research institutes all over the world (Kang et al. in IEEE Trans. Appl. Supercond. 17:1493-1496, ). In this paper, a sub-cooled liquid nitrogen cooling method is considered to design current lead parts for a 154 kV superconducting apparatus because of its excellent dielectric and mechanical characteristics (Kang et al. in IEEE Trans. Appl. Supercond. 17:1493-1496, ). Insulation gases such as SF, CF, and N are considered as suitable pressurization gases for enhancing the dielectric characteristics of a superconducting system in the Republic of Korea (Kang and Ko in IEEE Trans. Appl. Supercond. 21:1332-1335, ). Dielectric experiments are conducted on GFRP (glass fiber reinforced plastic) and insulation gases (SF, CF, and N) with various pressures to establish experimental criteria for designing current lead parts for superconducting applications. It is found that the criteria for calculating electrical breakdown voltage at sparkover of GFRP and insulation gases conform to the mean electric field intensity and the maximum electric field intensity, respectively. Also, the criteria for calculating the electrical breakdown voltage at sparkover according to various conditions are derived. Finally, the conceptual dielectric design of current leads for a 154 kV superconducting apparatus by applying the presented criteria is performed considering various safety factors. [ABSTRACT FROM AUTHOR]

Abstract: Recently, YBCO coated conductor (CC) called as second generation (2G) wire has been developed rapidly. The CC has a stabilizer layer for protecting the wire during a quench of the wire. In resistive superconducting fault current limier (SFCL), the stabilizer makes the resistance and limits the fault current during the fault. Therefore, specification of the stabilizer is one of important design factors in SFCL. This paper describes the current limiting characteristics of three coated conductors with respect to the specifications of the stabilizer. Two samples made by American Superconductors® have copper stabilizers attached by soldering. However, the two samples have not same structures. One has one-sided stabilizer, the other has both-sided stabilizer. On the other hand, another sample made by IGC-SuperPower® has copper stabilizer attached by electroplating, and the stabilizer layer surrounds the whole cross-section of the wire. Over-current tests of the three samples with various stabilizers were performed. Each sample has 8cm in length. From the results, the SFCL using the CC wire could be designed. [Copyright &y& Elsevier]

We fabricated a high-temperature superconducting (HTS) magnet with a persistent current switch (PCS) and evaluated the decay characteristics of persistent mode and joint resistance at 77 K. To make the HTS magnet, BSCCO(2223) tapes were wound into a double-pancake coil and connected to the PCS by soldering. Field decay behavior was remarkably dependent on operating current. At an operating current of 50% of the critical current (Ic), decay behavior showed two distinct regimes: initial fast decay and subsequent linear decay. By contrast, there was a linear decay regime of only 13% of Ic. Total circuit resistance was approximately 2.0 × 10-8 Ω at an operating current of 6 A. Measured decay behavior was closely consistent with the calculated decay behavior obtained from both the index resistance and joint resistance components. [Copyright &y& Elsevier]

• GFs were integrated with ANF through sol-hydrogel-paper process. • GF/ANF paper possess thermally conductive yet electrically insulating property. • Vibrational properties of GF and ANF were studied using ab initio calculation. • Superb mechanical properties with a remarkable toughness and strength were achieved. • Excellent thermal stability and nonflammability were obtained. Heat dissipation is a critical requirement for the innovation of fifth-generation (5G) electronics, and in turn, for the unceasing development of highly efficient heat-dissipating materials (HDMs). In 5G electronics, high thermoconductive yet electrically insulating HDMs with lightweight, excellent flexibility, and outstanding thermal properties have a high demand. In this study, we developed a fabulous HDM with superior mechanical properties, high thermal conductivity, and electrical insulation. The underlying principle involves taking advantage of graphene fluoride (GF), which is an emerging two-dimensional (2D) material that is highly thermally conductive, along with an electrically insulating material. By integrating a 2D GF sheet in a three-dimensional (3D) interconnected aramid nanofiber (ANF) network, a paper was successfully fabricated via a scalable process of sol-hydrogel-paper transformation. The resultant GF/ANF paper showed excellent mechanical properties with a remarkable strength of 188 MPa and toughness of 107 MJ m−3. These exceptional results are attributed to the formation of a nacre-inspired structure with strong hydrogen bonding between the GF sheet and ANF matrix and the extensive elongation of the entangled 3D ANF. Notably, the GF/ANF nacre-inspired paper with 40 wt% GF content achieved a thermal conductivity and volume resistivity as high as 48.2 W m−1 K−1 and 2.7 × 1015 Ω m, respectively. Moreover, the vibrational properties of GF and ANF were extensively investigated via ab initio calculations. The paper exhibited excellent thermal stability, non-flammability, and high efficiency in heat dissipation in an organic light-emitting diode system. It demonstrated the best overall performance among the representative HDMs analyzed, representing a critical breakthrough in the fabrication of HDMs toward practical applications in wearable electronic devices. [ABSTRACT FROM AUTHOR]