Electrical insulation characteristics of paper-ice composite insulating system in liquid nitrogen

In recent years, research work for realizing the high-temperature superconducting cable has advanced, where the development of electrical insulating system at cryogenic temperatures is one of the major researches. A composite insulating system made of insulating paper-LN/sub 2/ has been studied as one of the electrical insulating systems on the high-temperature superconducting cable. In paper-LN/sub 2/ composite insulating system, where the conventional techniques are used, microscopic bubbles remain inside the paper, and the partial discharge could occur easily. In order to overcome this problem, we have been studying the paper-ice composite insulating system as a substitute for paper-LN/sub 2/ of cryogenic electrical insulating system in high-temperature super-conducting cables. We found that AC electric strength (Fb) of paper-ice composite insulating system was higher than that of paper-LN/sub 2/ composite insulating system. Furthermore we found the existence of self-healing breakdown. This paper describes the breakdown characteristics and partial discharge resistibility of the paper-ice composite insulating system in LN/sub 2/.