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One of the critical components for high-voltage superconducting apparatuses, such as superconducting fault current limiters (SFCLs), superconducting cables, and superconducting transformers, is the termination part. The termination part supplies power to superconducting coils without insulating difficulties, and it is designed considering several conditions, such as temperature and pressure. Generally, the termination part for a high-voltage SFCL is divided by a spacer into SF6 and gaseous nitrogen (GN2) parts. To design an electrically reliable termination part, dielectric experiments on the sparkover and creepage discharge along the surface of a solid material in GN2 are performed, and the dielectric characteristics of the electric field intensity at the sparkover of GN2 and creepage discharge along the surface of a solid material in GN2 are expressed as an empirical formulae in terms of the field utilization factor ( $$\upxi$$ ). As a result, the electrical and mechanical design of the termination part including a spacer with respect to the material and shape is conducted. Finally, a conceptual design of the termination part for a 220 kV high voltage SFCL is proposed. The experimental results and design method proposed in this paper were applied to the design of the world’s largest commercial 220 kV/300MVA SFCL installed and operating in Moscow.

In this paper, a study on the design of the termination part for a 23kV superconducting cable is conducted. Also, the design of a spacer is derived in consideration of electrical and mechanical safety factors. In general, the termination part of a superconducting cable is filled with gaseous nitrogen (GN2) and gaseous sulphur hexafluoride (SF6), and may have a temperature gradient from cryogenic to room temperature. Therefore, a design considering the dependency of dielectric characteristics on temperature should be conducted. In this study, the criterion of electric field intensity on the creepage discharge characteristics between a solid and gaseous insulation material according to several conditions is derived through dielectric experiments. Also, overall design of the termination part for a 23kV superconducting cable is proposed considering the mechanical as well as electrical safety factors.

Cross Linked Polyethylene (XLPE) has been widely used as an insulation material of a power cable due to its excellent electrical and mechanical properties. XLPE may cause an environmental devastation because it is not recyclable due to its thermosetting characteristics. Therefore, it is necessary to develop an insulation material which could be replaced with the conventional XLPE owing to its eco-friendly and good dielectric characteristics. In this paper, an analytic study on the comparison between conventional XLPE and six types of eco-friendly polypropylene (PP) samples developed by Hu-innovation Co. Ltd is conducted. As a result, the dielectric characteristics of PP according to manufacturing process are analyzed.

In this paper, mechanical stresses on railway traction line insulators are analyzed by structural analysis. In application of railway traction lines, insulators are not only used to insulate but also subjected to adverse environmental conditions and mechanical vibrations. Two kinds of test to verify the robustness of insulators are performed in this study. Cantilever load test and tensile force test are carried out to ensure the reliability and stability of railway traction line insulators. Structural analysis that focuses on cantilever load test and tensile force test is carried out by using COM

Solid insulation materials are mainly used in superconducting magnet electrical applications. Such insulation must not only have the desired mechanical properties but also electrical properties under cryogenic conditions. Glassfiber-reinforced polymer (GFRP) needs to be studied with respect to its cryogenic insulation properties in relation to alternating current voltages with the current at maximum power (AC, Imp) (Kwang et al. , 2007). A voltage lower than that at which dielectric breakdown occurs leads to creepage discharge, which causes the dielectric strength to decrease and results in electrical accidents; therefore, we need to study the properties of creepage discharge. In this paper, we present the results of experiments on the properties of creepage discharge inside GFRP with gaseous (GN2) and liquid (LN2) nitrogen (Bansal et al. , 2008). The experimental results showed that the creepage discharge voltage increased with increasing creepage distance and pressure under LN2 and GN2 conditions (Hwang et al. , 2012). In addition, the creepage discharge electric field value was confirmed by FEM analysis. We checked the safety factor through simulation to apply the outcome of these experiments to the design of electrical applications.

The termination part of a high temperature superconducting apparatus such as a superconducting fault current limiter or a superconducting cable is usually insulated by pressurized SF 6 gas for its excellent dielectric strength. However, SF 6 condenses into LN 2 because of its high boiling point (approximately 209 K) during operation. The condensed SF 6 into LN 2 may result in problems such as dielectric degradation and system pressure decline. In order to prevent the condensation of SF 6 into LN 2 , the termination of an HTS apparatus is divided into two parts by using a spacer: an upper part pressurized by SF 6 with room temperature and a lower part pressurized by GN 2 with cryogenic temperature. The termination part should be operated in a high-pressure condition in order to ensure safe dielectric characteristics of HTS apparatuses. In this paper, dielectric characteristics as well as mechanical characteristics of a spacer under pressurized gas are conducted. It is well known that electrical breakdown may occur in the form of creepage discharge along the surface of a solid material rather than in the form of penetration sparkover through a solid or gaseous material. Experiments on the creepage discharge characteristics according to several solid materials under various pressures are conducted and a computer simulation using a finite element method is performed to analyze electric field distribution and mechanical strength of a spacer. Finally, the specifications of a spacer for 154 kV superconducting fault current limiters such as diameter, thickness, shape, and material, are suggested according to various safety factors.

To improve the NO2-sensing performance of single-walled carbon nanotube (SWCNT)-based sensors, zinc oxide (ZnO) nanoclusters (NCs) were functionalized by a microwave (MW)-assisted synthesis techniq...

Currently, the 28 GHz ECRIS (electron cyclotron resonance ion source) was developed to produce a high-current heavy-ion beam at the KBSI (Korea Basic Science Institute). The high-voltage platform of the 28 GHz ECRIS is essential to deliver an ion beam to the next acceleration stage. The high-voltage platform was designed considering dielectric characteristics in order to ensure electrical safety. In this paper, a study on the dielectric characteristics of GFRP (glass- fiber-reinforced plastic) is performed to determine the thickness of the GFRP cylindrical shell located between the plasma chamber and the warm bore of the superconducting magnet cryostat. The dielectric experiments on a GFRP cylindrical shell were conducted under a DC voltage. Sphere-to-plane electrode systems were used to examine the dielectric characteristics. Also, the relationship between the dielectric characteristics of the GFRP cylindrical shell and the distribution of the electric field intensity was calculated and analyzed by using FEM (Finite Elements Method) simulations.

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.

In the Korea Superconducting Tokamak Advanced Research (KSTAR), quench detection system using central difference averaging (CDA) and mutual inductance compensation (MIK) for central solenoid (CS) magnet has been studied. Similar to the cowound voltage taps, it is expected that this method can provide the good capability of rejecting inductive voltage noise. Accordingly, CDA and MIK method could be considered as a promising way. For this method to be an effective way, the inductive voltages should be accurately estimated, and then the measured CDA voltages are compared with the estimated ones. In previous studies, CS and poloidal field (PF) coils were modeled as the ideal solenoids to calculate mutual inductances between them. However, the nonlinearity of inductances due to Incoloy-908 jackets of PF1-PF5 coils that are ferromagnetic materials still needs to be compensated for more accurate estimation of inductive voltages. In this paper, the inductive voltages were estimated by considering the ferromagnetic effect of Incoloy-908 jackets to compensate the error voltages. Based on this study, the effect of Incoloy-908 on accuracy and reliability of CDA and MIK quench detection scheme was analyzed and discussed.

Rotary HTS flux pumps are suitable for cryogenic applications, where it is difficult to implement direct physical connections between the device in question and an external power supply. Here we examine the proportional-integral-derivative (PID) control of a rotary HTS flux pump to compensate for a change in the current in the HTS field coil of a synchronous motor under operating conditions. The field coil current must be maintained constant to prevent output fluctuation of the synchronous motor. In this context, a prototype of the rotary HTS flux pump with rotating HTS tape is constructed for a synchronous motor in this study. A 600-turn electromagnet is used to inject magnetic flux into the HTS tape to charge the HTS coil. The magnetic field of the electromagnet is controlled via PID control with respect to the rotational speed and rotating direction of the machine. As a result, we successfully compensate for change in the current of the HTS coil by controlling the magnetic field of the electromagnet, while the rotating speed and direction are varied.

Degradation of critical current ( I c) in a high-temperature superconducting (HTS) tape under bending conditions had been previously investigated. These investigations were focused on only either bending or torsion. A rotating flux pump is used to study the charging characteristics of an HTS synchronous motor. In order to design the rotating flux pump connected in series, the elliptical winding applied together with combined bending and torsion is essential. Therefore, in this paper, the critical current considering curvature of elliptical shape is measured with regard to nine kinds of mandrels. The shapes of the mandrels are a tall prolate ellipsoid, oblate ellipsoid, and semicircle. The diameters of each shape are 20, 30, and 40 mm, respectively. The experiments are mainly composed of three conditions: straight, bending, and combined bending and torsion. Finally, the experimental observations have been compared with the theoretical predictions.

High-temperature superconductors (HTSs) have a much larger thermal margin than low-temperature superconductors, owing to their high critical temperatures. This characteristic allows HTS magnets to tolerate extremely high heat loads that may arise from radiation. Therefore, research on the development of HTS quadrupole magnets is progressing widely. Quadrupole magnets are commonly used for focusing the transported beams of particles in accelerators. In order to focus the beam, the quadrupole magnet uses an iron yoke with a hyperbolic contour. However, the iron yoke induces nonlinear magnetic characteristics because of saturation. Therefore, an air-core HTS quadrupole magnet is proposed to improve the magnetic characteristics. In this paper, we design air-core and iron-core HTS quadrupole magnet models using a harmonic matching method. The field gradient and effective length of both magnets are 12.1 T/m and 550 mm, respectively. In order to verify the performances of the proposed air-core quadrupole magnet, the magnetic field gradient, field uniformity, and effective length are analyzed for operating currents ranging from 50 to 400 A.