• Progress in Superconductivity and Cryogenics
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• v.10 no.3
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• pp.32-35
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• 2008

A common problem in many fields of cryogenic power engineering is applying high voltage to cold parts of superconducting apparatus. In many cases, a bushing provides electrical insulation for the conductor which makes the transition from ambient temperature to the cold environment. The 60 kV class cryogenic high voltage bushing for neutral line of the 154 kV / 100MVA high temperature superconducting (HTS) transformer was described. The bushing is energized with the line-to-ground voltage between the coaxial center and outer surrounding conductors; in the axial direction, there was a temperature difference from ambient to about 77 K. For the insulation design of cryogenic bushing, electrical insulation characteristics of the GFRP were discussed in this paper.

• Progress in Superconductivity and Cryogenics
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• v.14 no.4
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• pp.20-23
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• 2012

Superconducting equipment has been actively investigated for securing the environment and energy technology (ET) in various parts of the world. Despite these movements, a high voltage cryogenic bushing, which plays an important role of interconnection between the electric power systems and superconducting devices, has not been fully developed due to severe insulation requirements. A gas insulated cryogenic bushing has been investigated as one of our projects since 2010. As a basic step to obtain the design parameters for cryogenic bushing, we focused on the surface flashover characteristics of glass fiber reinforced plastic (FRP) in several insulation gases. For the surface flashover tests, several insulation gases including $SF_6$, $CF_4$ and $N_2$ gas were prepared. Various length of FRP specimens were fabricated in order to obtain the fundamental data for creepage distance of FRP. The first specimen group was from 2 mm to 10 mm with 2 mm intervals and the second specimen group was from 20 mm to 100 mm with 20 mm intervals. And the gas pressure was varied from 1 bar to 4 bar. An AC overvoltage test and a lightning impulse test were performed. Then the experimental results of surface flashover were obtained and analyzed. Based on these results, it would be possible to design the optimum creepage distance of FRP in a cryogenic bushing.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.216-217
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• 2006

A common problem in many fields of cryogenic power engineering is to apply high voltage to cold parts of superconducting equipment. In many of these cases a bushing provides electrical insulation for the conductor which makes the transition from ambient temperature to the cold environment. The cryogenic high voltage bushing for the 154kV, 100MVA high temperature superconducting(HTS) transformer is described. The bushing 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 the insulation design of cryogenic bushing, the arrangement of condenser cone and electrical insulation characteristics of GFRP, Air, $LN_2$ and $GN_2$ were discussed in this paper.

• Progress in Superconductivity and Cryogenics
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• v.12 no.3
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• pp.12-15
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• 2010

Important key technologies of high-$T_c$ superconducting (HTS) transformer may include the HTS wire technology, bushing technology, cooling technology, AC loss, reduction technology, large current technology, and cryogenic temperature insulation technology. From among others, the cryogenic temperature insulation technology may be specifically a core technology for ensuring reliability for the smaller size, stability, economic efficiency, and power supply of a transformer. Therefore, the electric insulation technology of a superconducting transformer should be prerequisite. Such relevant studies are ongoing, but still, they are very insufficient for establishing the cryogenic insulation technology as of yet. Therefore, this paper simulated HTS transformer applied with continuous transposed conductor (CTC), which has been studied as a way of reducing AC loss. Also, the paper analyzed the insulation configuration of HTS transformer and bushing, and, accordingly, reviewed various characteristics of insulation breakdown out of liquid nitrogen. Thus, the paper constituted insulation database, and it is going to design the insulation of a transmission class HTS transformer and bushing.

• Progress in Superconductivity and Cryogenics
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• v.15 no.3
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• pp.20-23
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• 2013

In the development of high temperature superconducting (HTS) power machines, HTS bushing is one of core technologies. In particular, the insulation body with sheds and electrical insulation at cryogenic temperature have attracted a great deal of interest from the view point of the size, weight and efficiency of bushing. In this study, the electrical and mechanical characteristics of various insulators for body in liquid nitrogen ($LN_2$) were investigated. And the surface discharge distance, collar length of GFRP sheds were studied. To emit bubbles between sheds, the shape and arrangement of shed were studied. The shed structure for 60 kV class HTS bushing were designed with regular arrangement.

• Progress in Superconductivity and Cryogenics
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• v.13 no.4
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• pp.10-13
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• 2011

For the operation of high temperature superconducting (HTS) power equipments, it is necessary to develop insulating materials and high voltage (HV) insulation technology at cryogenic temperature of bushing. In this paper, the surface flashover characteristics of various insulating materials in $LN_2$ are studied. These results are studied at both AC and impulse voltage under a non-uniform field. The negative impulse breakdown voltage of GFRP is slightly higher than the positive impulse breakdown voltage. The use of glass fiber reinforced plastic (GFRP) and polytetrafluoroethylene (PTFE, Teflon) as insulation body for HTS bushing should be much desirable. Especially, GFRP is excellent material not only surface flashover characteristics but also mechanical characteristics at cryogenic temperature. The surface flashover is most serious problem for the shed design in $LN_2$ and operation of superconducting equipment.

• Progress in Superconductivity
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• v.13 no.1
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• pp.24-27
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• 2011

High voltage insulation in cryogenic environment is one of big issues for development of superconducting power application, such as superconducting fault current limiter, transformer, transmission cable, and so on. We had proposed a composite solid insulator composed of plastics and polymer insulation sheets for a use of high voltage superconducting power applications. It is well known that the G10 FRP keeps its mechanical strength at very low temperature and the PPLP is very good insulator adopted as insulations for superconducting transmission cables. The composition of these two materials will show very good electrical and mechanical properties adequate for the insulation components of superconducting power applications, such as bushing, insulation barrier, and even for a cryostat. Dielectric strengths of prepared samples were measured at the temperature of boiling point of liquid nitrogen at atmospheric pressure, which will be presented in this paper to show a usefulness of this technique.