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High-temperature superconducting (HTS) dc cable is expected to be an application as larger transmission of electrical power because of, ultimately, lower loss, as well as large capacity compared with ac cable. In order to secure long life, reliability, and compactness of HTS DC cable, the roles of breakdown properties and insulation design are important. In actual cable, breakdown properties are influenced by not only up-scale effect but also mechanical stress during cable production and installation. For HTS cable, polypropylene laminated paper has been used as insulation material. Polypropylene laminated paper has been widely adopted as insulating material for HTS cable. In this paper, the model cables with different thicknesses were fabricated, and the breakdown tests were performed. Based on the results, an improved insulation design of 250-kV-class HTS dc cable was proposed with volume effect. The breakdown characteristics of bended cables were also investigated with various testing conditions.

One of the expected systems on the power transmission aspect of high capacity and lower loss is the high-temperature superconducting (HTS) dc cable system. In an HTS dc cable system, the components with insulation system mainly consist of a superconducting power cable, a cable joint, and termination bushing at cryogenic temperature. The superconducting power cable is composed of a former, a superconducting conductor, and polypropylene laminated paper (PPLP) as insulation material impregnated with liquid nitrogen (LN 2 ). The cable joint, which is used to connect cables in joint boxes, has a central copper conductor surrounded by an insulating spacer such as epoxy and PPLP. The cryogenic parts of termination bushings are immersed in LN 2 with glass-fiber reinforced plastic used as insulator. This paper reports basic dielectric characteristics of insulation materials for the HTS dc cable system mainly composed of power cable, cable joint, and termination bushing. These results are studied under dc and lightning impulse voltage.

The development of high temperature superconducting (HTS) dc cable system has been promoted for the land long-term high-capacity power transmissions, submarine cables and renewable energies. Polypropylene laminated paper (PPLP) has been widely used as insulating material for HTS cable. To develop the PPLP-insulated dc cable, it is important to study the dc, dc polarity reversal and lightning impulse characteristics at a cryogenic temperature. In this paper, we discuss the electrical insulation characteristics of PPLP-insulated mini-model cable. We investigate the dc, impulse breakdown strength, dc polarity reversal, and dc voltage (V)-numbers of dc polarity reversal (N). Also, based on these results, the insulation design of 250 kV class HTS dc cable is performed.

A high-temperature superconducting (HTS) dc cable system consists of cable, termination, and cable joint. Polypropylene laminated paper (PPLP) and epoxy have been widely used as insulating material for HTS cable and cable joint. The electrical and mechanical characteristics of insulating materials at cryogenic temperature must be investigated for the long life, stable operation, and compactness of the cable. In order to develop an HTS dc cable and cable joint, it is important to understand the fundamental properties of insulating materials. In this paper, we discuss mainly about the electrical and mechanical characteristics of insulating materials for HTS dc cable and cable joint. We investigate the characteristics of dc and impulse voltage. The flashover and breakdown characteristics of PPLP, epoxy, and composite of epoxy-PPLP are studied. In addition, the mechanical characteristic such as tensile strength of PPLP at 77 and 300 K is discussed.

This paper reports empirical and numerical analyses on the electrical behavior of no-insulation (NI) coil. The spiral and radial current flows of NI coil in the case of the nominal operation and over-current condition are quantitatively identified using numerical analysis. Moreover, the origins of charging/discharging delays and magnetic field saturation are discussed in detail. Experimental results are also compared with the simulations to validate the numerical approach.

The HTS transformer is one of the promising HTS power applications that are expected to be commercialized in the near future. Among the auxiliary functions of a transformer, the voltage regulation function is known to be the most important one. For the voltage regulation of HTS transformers, they are normally equipped with the on-load tap changers (OLTC). It is also required that, in order to develop a HTS transformer as a complete system, not only the basic technologies for all the components including OLTC and bushing, but also the technologies for the insulation of these components at a cryogenic temperature should be well established as applicable. Taking such facts into account, the breakdown characteristics of the insulation components have been evaluated for such application areas as turn-to-turn insulation, layer-to-layer insulation, c, drive shaft-to-drive shaft insulation, tap connecting terminal insulation and others. In overall, this paper discusses the electric insulation design and experimental results with regard to HTS transformer, OLTC and bushing.

The basic electrical insulation design of 2.5 MJ conduction cooling high temperature superconducting magnetic energy storage (HTS SMES) have been studied in this paper. The high voltage is generated both ends of magnet of HTS SMES by quench or energy discharge. Therefore, the insulation design of the high voltage needs for commercialization, stability, reliability and so on. In this study, we analyzed the insulation composition of a HTS SMES, and investigated about the insulation characteristics of the materials such as Polyimide, Al2O3 , GFRP and vacuum at cryogenic temperature. Base on these results, the basic insulation design for 2.5 MJ conduction cooling HTS SMES was performed.

The electrical insulation design of 600 kJ conduction cooled high temperature superconducting magnetic energy storage (HTS SMES) has been studied in this paper. High voltage is generated to both ends of magnet of HTS SMES by quench or energy discharge. Therefore, the insulation design of the high voltage needs for stability and reliability to allow commercialization. In this study, we analyzed the insulation composition of a HTS SMES, and investigated about the insulation characteristics of materials such as Kapton, AlN,Al2O3, GFRP and vacuum at cryogenic temperatures. Based on these results, the insulation design for 600 kJ conduction cooled HTS SMES was performed.

The breakdown and voltage-time characteristics of turn-to-turn models for point contact geometry and surface contact geometry using copper multiwrapped with polyimide film for a high-temperature superconducting transformer were investigated under ac and impulse voltage at 77 K. Polyimide film (Kapton) 0.025 mm thick is used for multiwrapping of the electrode. As expected, the breakdown voltages for the surface contact geometry are lower than that of the point contact geometry, because the contact area of the surface contact geometry is lager than that of the point contact geometry. The time to breakdown t 50decreases as the applied voltage is increased, and the lifetime indexes increase slightly as the number of layers is increased. The electric field amplitude at the position where breakdown occurs is about 80% of the maximum electric field value.

This study examined the purification of wastewater from the chemical mechanical polishing (CMP) process via a superconducting high gradient magnetic separation (HGMS) system. To remove silica, the main contaminant in CMP wastewater, the optimal coagulation process of silica-magnetite-ferric hydroxide aggregates was empirically determined. Filtration tests via superconducting HGMS system with optimal coagulation process were conducted with respect to the magnetic field and wastewater flow rate. The turbidity and Si concentration of the wastewater filtered at 2 T and 400 mL/min were in accordance with the grey water standard and reverse osmosis (RO) feed water requirement, which demonstrated the feasibility of the superconducting HGMS system for the purification of CMP wastewater.