Article

Breakdown Characteristics of Liquefied SF6 and CF4 Gases in Liquid Nitrogen for High Voltage Bushings in a Cryogenic Environment

IEEE Transactions on Applied Superconductivity (Impact Factor: 1.32). 06/2011; 21(3):1430-1433. DOI: 10.1109/TASC.2010.2090638

ABSTRACT Highvoltagecryogenicinsulationissuesneedtobead- dressed in order to promote the commercialization of high temper- ature superconducting (HTS) equipment. One of the critical com- ponents for superconducting devices is the bushing whose role is to safely supply high current to the device. Due to a steep tem- peraturegradient,commercialbushingswhichhavebeeninsulated with gas could not be directly applied to cryogenic equipment due to liquefaction of in the cryogenic environment; there- fore, alternative suitable structure and insulation methods should be developed. As a fundamental step in the development of the op- timum bushings for HTS devices, the breakdown characteristics of liquid nitrogen mixed with liquefied insulating gases such as , and have been investigated. In particular, we noted the insulation characteristics of gas whose liquefication tempera- ture is much higher than gas. Thus, in order to investigate the possibility of substituting gas for gas for the bushings of HTS electrical equipment, impulse tests, AC withstanding voltage tests, and partial discharge (PD) tests have been performed. As a result of these tests, it was shown that mixtures of liquefied insu- lating gases have a much higher breakdown voltage compared to pure liquid nitrogen. Especially in a cryogenic environment, the usage of gas should be evaluated due to freezing effects. On the other hand, gas has shown excellent insulation properties even in a cryogenic environment and could be utilized as an insu- lation gas for high voltage bushings of HTS electrical equipment.

1 Follower
 · 
46 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: One of the critical matters yet to be solved for commercial applications of extra high voltage superconducting devices is the optimum design and development of high voltage cryogenic bushings which could withstand both severe insulation requirements and a steep temperature gradient due to the cryogenic environment. Neither conventional extra high voltage bushings insulated by ${\rm SF}_{6}$ gas nor composite materials are directly applicable to cryogenic bushings due to an extremely low temperature environment. In order to obtain suitable dielectric performance of bushings in the cryogenic environment, we focused on an alternative insulation gas instead of ${\rm SF}_{6}$ such as ${\rm CF}_{4}$, which shows excellent dielectric performance under extremely low temperatures, and also on the optimum design of cryogenic bushings, which have a longer creepage distance compared to conventional bushings. In this paper, design factors of cryogenic bushings were discussed, and test results of 60 and 100 kV extra high voltage prototype bushings were discussed in detail. Consequently, it was possible to obtain satisfactory results to verify the insulation level of newly designed extra high voltage cryogenic prototype bushings for superconducting electric power applications.
    IEEE Transactions on Applied Superconductivity 06/2012; 22(3):7701204-7701204. DOI:10.1109/TASC.2011.2177629 · 1.32 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: One of the critical components to be developed for high-voltage superconducting devices, such as superconducting transformers, cables, and fault current limiters, is a high-voltage bushing to supply a high current to devices without insulation difficulties in cryogenic environments. Unfortunately, suitable bushings for high-temperature-superconductivity (HTS) equipment have not been fully developed to address cryogenic insulation issues. As a fundamental step towards developing the optimum design of the 154 kV prototype SF6 bushing of HTS devices, the puncture and creepage breakdown voltages of glass-fiber-reinforced-plastic (GFRP) were analyzed with a variety of configurations of electrodes and gap distances in the insulation material. And design factors of high-voltage cryogenic bushings were obtained from the result of tests. Finally, the withstand voltage tests of manufacturing a 154 kV extra-high-voltage (EHV) prototype bushing has been performed. Consequently, we verified the insulation level of the newly designed 154 kV EHV cryogenic prototype bushings for superconducting electric power applications.
    Japanese Journal of Applied Physics 09/2012; 51(9). DOI:10.1143/JJAP.51.09ME01 · 1.06 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Recently, the superconductivity projects to develop commercial superconducting devices for extra high voltage transmission lines have been undergoing in many countries. One of the critical components to be developed for high voltage superconducting devices, including superconducting transformers, cables, and fault current limiters, is a high voltage bushing, to supply high current to devices without insulating difficulties, that is designed for cryogenic environments. Unfortunately, suitable bushings for HTS equipment were not fully developed for some cryogenic insulation issues. Such high voltage bushings would need to provide electrical insulation capabilities from room temperature to cryogenic temperatures.In this paper, design factors of cryogenic bushings were discussed and test results of specimen were introduced in detail. First, the dielectric strength of three kinds of metals has been measured with uniform and non-uniform electrodes by withstand voltage of impulse and AC breakdown test in LN2. Second, puncture breakdown voltage of glass fiber reinforced plastics (GFRPs) plates has been analyzed with non-uniform electrodes. Finally, creepage discharge voltages were measured according to the configuration of non-uniform and uniform electrode on the FRP plate. From the test results, we obtained the basic design factors of extra high voltage condenser bushing, which could be used in cryogenic environment.
    Physica C Superconductivity 01/2013; 484:338–342. DOI:10.1016/j.physc.2012.03.036 · 1.11 Impact Factor
Show more