Application of New Cryogenic Electrical Insulating System of High-Temperature

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The investigators have been studying the application of paper-ice composite insulating System to electrical insulation system of superconducting power cables. The superconducting cables is the promising ways for handling huge electric power efficiently in the future. It is necessary to study the behavior of the electrical insulation system at cryogenic temperature to evaluate long term reliability as a superconducting cable.The results are summarized as follows :(1) In paper-ice composite insulating system, the difference of electric strength (Fb) due to type of papers between kraft paper and PPLP (Polypropylene Laminated Paper) decreased and the breakdown characteristics was mainly dominated by ice.(2) The life time of the paper-ice composite insulating system was longer than the paper-liquid nitrogen composite insulating system, and the paper-ice composite insulating system using the high density kraft paper had the longest life time.(3) AC electric strength of paper-ice composite insulating system was higher than that of paper-liquid nitrogen composite insulating system, and that the breakdown appeared to be a self-healing type.(4) The inception electric field strength (Ei) and extinction electric field strength (Ee) of the partial discharge on the paper-ice composite insulating system were also higher than the paper-liquid nitrogen composite insulating system, and in the case of the paper-ice composite insulating system using high density kraft paper, the highest Ei and Ee were obtained.In conclusion, paper-ice composite insulating system is considered to be one of the best for cryogenic electrical insulating system such as high-temperature superconducting cables.