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 (GN 2 ) and cryogenic nitrogen gas (CGN 2 ) 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 (LN 2 ), GN 2 and CGN 2 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 CGN 2 is also influenced by temperature and vapor-mist density of the gas.Index Terms-Cryogenic insulation, HTS cable termination insulation, surface discharge, volume breakdown.

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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.

A Bi-2223 tape has been developed for power applications such as a fault current limiter, a power cable and a superconducting magnetic energy storage system (SMES). In such applications, the Bi-2223 tape carries time varying transport current and in addition experiences time varying external magnetic field. It is well known that the external magnetic field not only causes magnetization loss in the Bi-2223 tape, but also drastically increases transport loss due to a so-called "dynamic resistance". We developed an evaluation setup, which can measure transport loss in an external AC magnetic field. Using this equipment, we measured the dynamic resistances for various amplitudes and frequencies of external AC magnetic field perpendicular to the face in the tape. Simultaneously we investigated the effect of external AC field on transport loss with different experimental conditions. This paper describes test results and discussions on correlation between the dynamic resistance and the transport loss for various technical Bi-2223 tapes.

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