Dong-Soon Kwag

The Electrical Insulation Characteristics for a HTS Cable Termination

A research on several characteristics such as volume breakdown and surface discharge of insulators for a termination of power transmission class high temperature superconducting (HTS) cable was performed. In this paper, we investigated the surface discharge of glass fiber reinforced plastic (GFRP) in the air, nitrogen gas (GN2) and cryogenic nitrogen gas (CGN2) media. The breakdown characteristics of these media were also studied. Experimental results revealed that flashover voltage greatly depends on pressure, temperature, the kinds of insulating media and voltages. However, it is shallowly affected by shape and material of electrode. The breakdown voltage of liquid nitrogen (LN2), GN2 and CGN2 deeply depends on the shape and dimension of electrode, kinds of voltages and pressure. Moreover, the breakdown voltage of CGN 2 and flashover voltage of GFRP in the CGN2 is also influenced by temperature and vapor-mist density of the gas

Research on the Insulation Design of a 154 kV Class HTS Power Cable and Termination

A 154 kV class high-temperature superconducting (HTS) power cable system Is developing in Korea. For insulation design of this cable, the grading method of insulating paper is proposed. The electrical insulation material has been used two kind of laminated polypropylene paper (LPP) that has different thickness. The use of graded insulation gives improved mechanical bending properties of the cable. Also, within a HTS cable technology the terminations are important components. A HTS cable termination is energized with the line-to-ground voltage between the coaxial center and outer surrounding conductors, in the axial direction there is a temperature difference from ambient to about 77 K. For insulation design of this termination, the insulation material of the termination body used glass fiber reinforced plastic (GFRP) and the capacitance-graded method is proposed. Therefore, in order to insulating design of a 154 kV class HTS power cable and termination, this paper will report on the experimental investigations in impulse breakdown and surface flashover characteristics of the insulation materials. Based on these experimental data, the electrical insulation design of a 154 kV class HTS power cable and termination were calculated.

AC Flashover Voltages Along Epoxy Surfaces in Gaseous Helium Compared to Liquid Nitrogen and Transformer Oil

Gaseous helium at high pressure is regarded as a potential coolant for superconducting cables. The dielectric aspects of cryogenic helium gas are both complex and demanding. In this experimental study, we looked at the interface between a smooth epoxy surface and high pressure helium gas in a homogeneous electric field. The ac flashover voltages of epoxy samples whose heights are 3 and 5 mm of diameters 9.5, 12.7, and 19 mm are presented. The results have been analyzed using Weibull statistics. In addition to the behavior of the epoxy in gaseous helium as a function of pressure and temperature, we also present data of the characteristics of the epoxy surface in transformer oil at 293 K and in liquid nitrogen (77 K). The breakdown characteristics of a uniform field gap in gaseous helium as a function of pressure and temperature under ac, dc, and lightning impulse voltages are also given. Field calculations have been made for one of the experimental geometries in an attempt to explain some of the anomalies in the experimental results. The results show that cold compressed helium gas is a viable dielectric but requires different insulator designs compared to insulators for liquid nitrogen.

Electrical Insulation Design and Experimental Results of a High-Temperature Superconducting Cable

A 22.9 kV/50 MVA class high-temperature superconducting (HTS) power cable system was developed in Korea. For the optimization of electrical insulation design for HTS cable, it is necessary to investigate the ac and impulse breakdown and partial discharge inception stress of the liquid nitrogen (LN2)/ laminated polypropylene paper (LPP) composite insulation system. These results were used to insulation design of the model cable for a 22.9 kV class HTS power cable and the model cable was manufactured. The insulation test of the manufactured model cable was evaluated in various conditions and was satisfied standard technical specification in Korea. Based on these experimental data, the single-phase and three-phase HTS cable of a prototype were manufactured and verified.

Insulation studies and experimental results for high Tc superconducting power cable

In this paper, we studied electric insulation characteristics of synthetic Laminated Polypropylene Paper (LPP) in liquid nitrogen (LN/sub 2/) for the application to high temperature superconducting (HTS) cable. And, we selected the insulation paper/LN/sub 2/ composite insulation type for the electric insulation design of a HTS cable. Furthermore, we compared the breakdown characteristics of the butt gap and bent mini-model cable that comes into being in this kind of cryogenic insulation type. It is necessary to understand the winding parameter of insulation paper/LN/sub 2/ composite insulation.

A study on the composite dielectric properties for an HTS cable

In order to optimize the insulation design of a cold dielectric high temperature superconducting (HTS) cable, the composite insulation system has been investigated according to the arrangement of laminated polypropylene paper (LPP) and kraft paper in liquid nitrogen. LPP is a prominent insulating material with a high dielectric strength and low dielectric loss, which has been used previously as a HTS cable insulating materials. In addition kraft paper has been used for oil-field (OF) cable as insulating materials for a long time. In this paper, the dielectric properties on composite insulation system according to the arrangement of LPP and kraft paper was compared. The economic and dielectric performances of two insulating materials were considered and applied toward a HTS cable. Furthermore, from an economic satisfaction point the most suitable arrangement, and compared the dielectric properties of the mini-model cables were examined.

Insulation test of reciprocal and concentric winding arrangement for a HTS transformer

In Korea, the Hyosung Industrial, Korea Polytechnic University and Gyeongsang National University are developing a power distribution and transmission class HTS transformer that is one of the 21st century superconducting frontier projects. For the development, it is necessary to establish the dielectric technology at cryogenic temperature such as insulating design, cooling system, manufacture, compact, and so on. Also, verification of insulating stability is an important dielectric technology. Therefore, we prepared two models, one is concentric arrangement, the other is reciprocal arrangement, from Kapton insulated Cu tape for a small simulated HTS transformer and measured their insulation characteristics such as PD, ac (50 kV, 1 min) and impulse (154 kV, 1.2/spl times/50 /spl mu/s) withstand test. Before manufacture of each model, we have analyzed insulation composition and investigated electrical characteristics such as breakdown of LN/sub 2/, polymer and surface flashover on FRP in LN/sub 2/. We are going to compare with measured each value and apply the value to most suitable insulating design of the HTS transformer.

Insulation Design and Experimental Results for Transmission Class HTS Transformer With Composite Winding

In the response to the demand for electrical energy, much effort aimed to develop and commercialize high temperature superconducting (HTS) power equipments has been made around the world. In Korea, companies and universities are developing a power distribution and transmission class HTS transformer that is one of the 21st century superconducting frontier projects. The composite winding of transmission class HTS transformer is concentrically arranged primary winding (High)-Secondary winding (Low)-tertiary winding (High) from center. Primary winding is continuous disk type, Secondary winding is layer type and tertiary winding is Double pancake type. For the development of transmission HTS transformer with composite winding, the cryogenic insulation technology should be established. We have been analyzed insulation composition and investigated electrical characteristics such as breakdown of , barrier, kapton films and surface flashover on Fiber Reinforced Plastic (FRP) in Liquid nitrogen . We are going to compare with measured each value and apply the value to most suitable insulating design of the HTS transformer.

The Insulation Characteristics of Coil—Cryocooler for Conduction Cooled HTS SMES

The conduction cooled high-temperature superconductor (HTS) SMES (superconducting magnetic energy storage) was operated in cryogenic temperature and high vacuum conditions. Thus, the insulation design at the conditions is an important element that should be established to accomplish compact design is a big advantage of HTS SMES. However, the behaviors of insulators for the conditions are virtually unknown. Therefore, we need to researches and development of insulation concerning application of the conduction cooled HTS SMES. In this study, we experimented on insulation characteristics of SMES system. Also, we investigated about insulation characteristics of suitable materials to insulator for conduction cooled HTS SMES. As these results, we had basic data for insulation materials selection and insulation design of cryocooler-to-magnet coil for the development of 600 kJ class conduction cooled HTS SMES.

A study on thickness effect of HTS cable for insulation design

The electrical insulating design is important to realize the HTS (high temperature superconducting) cable because this cable is operated under the high voltage environment. For the insulation design of HTS cable, it is necessary to investigate the PD (partial discharge) inception, ac and impulse breakdown strength of LN2 (liquid nitrogen)/LPP (laminated polypropylene) composite insulation system. However, the designed insulation thickness by ac and impulse could not be applied to cable fabrication process due to much low electrical breakdown strength. The effect of the multi-layered insulation paper was not considered on the previous insulation design and the insulation thickness by PD inception strength could be applied only. In this paper, the electrical breakdown characteristic, which considered the effect of multi-layered of LPP, was investigated to design the insulation thickness.