Search

This paper reports the feasibility of the impregnation of no-insulation (NI) high-temperature superconducting (HTS) coils using an electrically conductive epoxy resin. Recently, several studies of HTS coils without turn-to-turn insulation have been reported for field coils used in rotating machines such as motors and generators. The NI winding technique enhances the thermal stability of the HTS coil without requiring complicated protection techniques because the quench current is automatically bypassed through the turn-to-turn contacts within the HTS coil. Nevertheless, there is still a question as to whether the NI technique can be applied to rotating machines. To utilize an HTS coil under high mechanical loads such as field coils for rotating machines, the HTS tapes must be stabilized mechanically. For HTS field coils intended for use in rotating machines, epoxy impregnation is generally necessary to protect the HTS field coil from mechanical disturbances caused by the magnetic field and rotational vibration of the rotor to enhance the mechanical stability [1], [2] . However, the NI HTS coil cannot be fabricated by wet winding using epoxy resin because epoxy resins such as Stycast 2850 FT and CTD 521 are electrically insulating materials. This study examines the electrical stability of an NI HTS coil impregnated with an epoxy resin containing electrically conductive particles. The results are likely to present useful data for the application of electrically conductive epoxy impregnated NI HTS coils to rotating machines. [ABSTRACT FROM PUBLISHER]

Because low-temperature superconducting (LTS) magnets can conduct large electric current and generate intense magnetic fields under cryogenic conditions, such magnets are used in many applications such as MRI, nuclear magnetic resonance spectrometers, and mass spectrometers. However, an abnormal termination called “quench” disturbs the normal operation and increases the magnet temperature. To protect the LTS magnet from excessive heat, the maximum temperature of a magnet under the quench process should be calculated. The design of a superconducting magnet protection system is performed according to the calculated maximum temperature. This is why accurate estimation of magnet temperature is important. The quench process of a superconducting magnet involves complex physical mechanisms, which requires a thermal–electrical simulation using computational analysis. We propose a highly efficient and reliable three-dimensional quench calculation method that can calculate the magnet temperature in the quench process. The LTS magnet is divided into many unit nodes; multiphysics analysis at each node is carried out with respect to the elapsed time. To verify the feasibility of the simulation, LTS magnet quench experimental results were compared with the simulation results. This study has the potential to develop a computational method for heat propagation analysis of a superconducting magnet. [ABSTRACT FROM PUBLISHER]

This paper describes new kind of HTS (High Temperature Superconducting) element for current leads, which can transfer large electric current in the nuclear fusion system. Since the HTS tapes have no resistance and the generated Joule heat is also very small compared to the conventional current leads, cooling costs of the current leads can be reduced. For this reason, the various feasibility researches for HTS current leads have been promisingly progressed in the superconducting power applications. However, there is a limitation on the capability of current carrying for single HTS tape. In addition, the cross-sectional area of the current leads should be small enough to minimize the heat conducted through the HTS current leads. In order to improve the current carrying capacity of the current leads, multiple HTS tapes are required. In this paper, we proposed several structures of compact HTS current leads and compare them other 2 kA class current leads. We report on the calculated characteristics of stabilized HTS current leads and on the performance measured during critical current measurement tests. [ABSTRACT FROM PUBLISHER]

A proto-type hybrid electro-magnetic suspension system (hybrid EMS system) was developed by Yonsei university refid="ref1"/ . It is the first step of study on fundamental technology for advanced railroad system development. The proto-type hybrid EMS system consists of a ferromagnetic-core, a superconducting magnet (Bi-2223) for generating magneto-motive force (MMF) and a control coil for levitation control. This system has the characteristic of a control coil generating a magnetic flux to keep the levitation gap in constant value when the gap is attempted to be varied by external physical factors. In doing so, the induced current by the magnetic flux generate loss to the superconducting magnet inducing the possibility of an unstable system. Therefore, we have experimented and documented the results of evaluating the loss in the superconducting magnet generated by the control coil. This paper can be expected to suggest useful data for the design and operation of a hybrid EMS system. [ABSTRACT FROM PUBLISHER]

This paper deals with the shape design of the iron-core of a hybrid EMS (electro-magnetic suspension) system. A proto-type hybrid EMS system was developed by Yonsei University in 2010 refid="ref1"/ , refid="ref2"/. It is the first step of study on fundamental technology for advanced railroad systems development. The hybrid EMS system requires cooling systems because it uses superconducting magnets refid="ref3"/ , refid="ref4"/. These cooling systems can influence costs to making and operating the hybrid EMS system. Therefore, a study to reduce the number of cooling systems needs to be carried out in order to economically commercialize the hybrid EMS system. In this paper, a method that reduces the number of cooling systems of the hybrid EMS system was proposed. To achieve this, a small-scale iron-core and coils assembly was fabricated. Using this system, characteristics of levitation force according to the structure of the iron-core was evaluated. Also, numerical analysis using the FEM tool in order to evaluate the levitation force and net force of a full-scale model was performed. This paper can be expected to suggest useful data for the design of a hybrid EMS system. [ABSTRACT FROM PUBLISHER]

Recently, the smart fault current controller (FCC) was proposed in order to apply to the smart grid. The smart FCC consists of an HTS coil, an AC/DC rectifier, and a control unit. A fault current should be immediately limited by the inductance of the coil at the first peak, and then adjusted by controlling the rectifier. The larger inductance of the coil induces the lower fault current. However, a large inductance coil requires high cost and large size. To reduce the HTS conductor consumption, an HTS coil with a reversely magnetized core (RMC) was proposed. To verify the concept, two permanent magnets were installed. In this paper, various model coils were fabricated and applied to the FCC system: 1) air core, 2) open iron core, 3) closed iron core, 4) open core with RMC, and 5) closed core with RMC. Based on a comparative study on the five models, an HTS coil with a closed RMC has the lowest first peak current. The first peak current in the proposed model was 27.8% smaller than that of air core case. The experimental results show that the proposed concept is to reduce the wire consumption. [ABSTRACT FROM PUBLISHER]

High temperature superconductor (HTS) is a promising material as current leads for large current applications, because it has zero resistance. However, a single HTS tape has limitation on the capacity of current rating due to the critical current of the HTS tape. Therefore, stacking or parallel structure of the HTS tapes is inevitable in high temperature superconducting current leads (HTSCLs) for large current application. In this paper, several stacking methods with respect to the shape of the current terminal and the structure of the HTS tape are studied and the characteristics of the stacked samples are investigated by experimental analysis. The critical currents of the HTS modules were measured and the conductive heat leakage of a stabilizer layer was calculated. From this analysis, the characteristics of the current distribution and decrease in the critical current of HTS modules with respect to the shape of the current terminal were obtained. Based on the results, the required stacking number of the HTS tapes for certain operating current HTSCLs can be calculated. [ABSTRACT FROM AUTHOR]

To design a large scale superconducting fault current limiter (SFCL) for power grids, a single long-length YBCO coated conductor (CC) wire is preferred. However this single YBCO CC wire can cause a problem of unequal voltage distribution between the parts on the long wire at quench by the faults. Inhomogeneous critical current of the YBCO CCs in the SFCL is a possibility. Furthermore, sub-cooled liquid nitrogen (LN2) condition is usually used to increase current capacity of the SFCL. However, this sub-cooled condition can worsen the inhomogeneity between the YBCO CCs. Therefore, it is important to understand the relation between the unequal voltage distribution and the inhomogeneous critical currents in the single long length YBCO CC. In this paper, experiments with the same single YBCO CC wire were conducted in various temperature conditions, LN2 and sub-cooled LN2. In both experiments, the critical currents and voltage distributions generated by faults at short-circuit tests were measured. It was observed that the inhomogeneous condition impacts on the unequal voltage distribution. [ABSTRACT FROM AUTHOR]

A non-inductive coil is an essential element of a resistive superconducting fault current limiter (FCL). A bifilar pancake type non-inductive coil, which is most common type, has two drawbacks; difficulty of paralleling tapes and a high risk of electrical breakdown at the terminal part. Although the bifilar type is simple as an element, large-scale FCL needs quite a number of series and parallel connections between elements. To make a non-inductive coil using conventional inductive elementary coils, we propose a novel structure of the coil. It looks like a toroid but entire inductance is near zero. This coil can overcome the drawbacks of conventional bifilar coil. In this paper, we confirm the new concept by numerical analyses. A few kinds of new models are compared, and then we concluded the proposed toroidal shape one is most suitable. This new structure coil can help implement of a hybrid FCL which is to generate the magnetic field at only fault. [ABSTRACT FROM AUTHOR]

This paper deals with the design and operating characteristics analysis of electromagnetic suspension (EMS) system. The EMS system consists of a rail, a U-shaped iron core, a high temperature superconductor (HTS) coil, a couple of DC control coils. The HTS coil generates a high magnetic field in the U-shaped iron coil and the rail. As wall as, the U-shaped iron core can be attracted by the coupled high magnetic field. We calculated turns and operating current conditions of HTS coil considering the decay of critical current when perpendicular magnetic fields are applied to the HTS coil. In addition to the design of the HTS coil, a Linear Quadratic (LQ) control method used to design the DC control coils that control the gap distance between the rail and U-shaped iron core. That is, if the gap distance is varied due to the several external disturbances, the DC control coils generated a magnetic field and then keep the constant interval. Thus, the operation of DC control coils would affect the magnetic flux density at the air gap. In this study, we verified the effect of distributions of magnetic flux density using finite element method (FEM) and MATLAB Simulink simulations. Furthermore, we numerically calculated the appropriate control current of DC control coils and the perpendicular magnetic field density on the HTS coil under the external disturbance. Based on these results, the appropriately combined current conditions and control method of EMS system to realize the stable levitation force were achieved. [ABSTRACT FROM AUTHOR]

This paper deals with design and operating tests of prototype hybrid superconducting fault current limiter (SFCL) which is series connected non-inductive solenoid resistive coil and asymmetric non-inductively wound coils. The role of resistive SFCL is for reducing the fault current in the first swing. Moreover, resistive SFCL can reduce a load of dielectric strength in hybrid SFCL. Two kinds of high temperature superconductor (HTS) wires were used to fabricate asymmetric HTS coil. These HTS wires had different quench characteristics such as different critical current and n-value. Unbalanced current distribution between two HTS wires in the asymmetric HTS coil during the fault should occur. Thus, the asymmetric HTS coil generates impedance and repulsive force from magnetic flux. The finite element method was performed to calculate maximum repulsive force. From experimental tests and FEM simulation results, proper combination of HTS wires and configuration of asymmetric HTS coil with fast switch were determined to increase maximum repulsive force. Also, the prototype hybrid SFCL with fast switch was fabricated and performed. [ABSTRACT FROM PUBLISHER]

Uncertainty and complexity due to expanded adoption of renewable energy resources, distributed energy resources as well as expanded electric transportation and dynamic demand response technologies in the power industry present significant challenges in grid operations. It is thus required to develop smart protection and control actions for ensuring highly reliable and healthy electric power infrastructure by increasing resiliency against component failures or natural disasters, i.e. self-healing ability. This paper, in particular focuses on the self-healing in the context of grid protection using smart superconducting fault current controller (Smart FCC). A systematic framework and technological requirements are presented for realizing the envisioned self-healing protection capability using Smart FCC while minimizing the electric loss near zero through superconducting coil. Illustrative examples, modeling and simulation studies demonstrate the validity and efficacy of the proposed framework and envisioned technology. [ABSTRACT FROM PUBLISHER]

A nuclear magnetic resonance (NMR) magnet composed of a high-temperature superconductor (HTS) is expected to contribute to a smaller size and a higher magnetic field (>1 GHz) of the NMR magnet due to its high critical current density under high magnetic field and better mechanical properties. The high operating temperature of HTS NMR magnets also makes conduction cooling by a cryocooler available. The conduction cooling system combined with a cryocooler is compact and user-friendly but has critical issues about the design of conduction cooling passages and the mechanical vibration. The small-scale HTS magnet with the conduction cooling system is fabricated and tested to check the issues and establish the design basis as a preliminary step for the development of a 400-MHz HTS NMR magnet. Thermal analysis for heat loads and thermal resistances at main joints is performed from the temperature distribution of the cooling system. The vibration levels at the crycooler and the vacuum chamber are discussed in comparison to the vibration criterion of NMR magnets. In addition, the design approach to the conduction cooling system for the HTS NMR magnet is discussed. [ABSTRACT FROM PUBLISHER]

A 3-T 100-mm winding bore conduction-cooled REBCO magnet has been designed, constructed, and tested. It consists of a stack of double pancake coils wound with metallic cladding (MC) REBCO tapes, for which 1–2 \mu \textm stainless steel was clad in a hermetic way around the tapes. This approach, first proposed by the SuNAM Company Ltd. in 2015, is expected to substantially reduce the charging time delay of a no-insulation magnet, which in turn will be effective in the manipulation of screening currents in such a way as to improve the field homogeneity of magnets, particularly for nuclear magnetic resonance or MRI. This paper presents test results for our approach on the current sweep cycling, which is used to reduce the screening current-induced fields in a newly constructed 3-T 100-mm MC all-REBCO magnet [ABSTRACT FROM PUBLISHER]

Recently various high temperature superconducting (HTS) conductors have been commercialized in the power applications. While a BSCCO becomes tape or wire, others coated conductors (CC) are tapes. An HTS magnet utilized with these conductors can be fabricated as a form of pancake winding or layer winding. In the case of HTS magnet using a thin and rectangular tape, the pancake winding method is satisfied in the practical cases because of its suitable features. However, one of the disadvantages of this winding method is increasing brands and splices. From this point of view, we propose a layer winding method using an HTS tape and fabricated HTS layer coils. To verify the feasibility of the proposed winding method, critical current and over-current tests are investigated in liquid nitrogen and the results are compared with those of pancake coils. In addition, operating characteristics on the condition of various winding tensions are analyzed. [ABSTRACT FROM PUBLISHER]

The prototype high-Tc superconducting electromagnet (HTS-EM) for high-speed EMS Maglev was successfully demonstrated in EMS system up to the vehicle running speed of 500 km/h. The EM was designed to interface with the existing propulsion system used in the German high-speed Maglev. The rating levitation force of the EM was designed to correspond to the weight of the EM at a 20 mm levitation gap. Electromagnetic forces were simulated and compared with the test results in order to verify the design feasibility of the HTS-EM. Operating tests revealed that the HTS-EM was fully operational in zero-power control mode. However, the operating current of the HTS coil was affected by the control current when the guideway disturbance occurred. The design feasibility and operability of the HTS-EM was verified in the study. [ABSTRACT FROM PUBLISHER]

The superconducting fault current limiter (SFCL) is a protection device for an electric power system. In other to design the SFCL, the temperature of the HTS tapes should be calculated under the over-current caused by fault condition. The structure and property of HTS tape have an effect on the temperature. [ABSTRACT FROM AUTHOR]