In order to realize bulk power transmission with high reliability and high efficiency, electric power companies have made efforts to connect several electric power systems together. In this case, fault current may exceed the rated current of such power devices as a circuit breaker and a power transformer in the case of contingency and they have to be replaced with the devices with the higher rated value. Fault current limiters (FCL) have been expected to be installed in an electric power system to suppress fault current and to prevent the replacement. This paper first reviews the necessity of FCL in electric power system, and R & D status of various types of FCL in the world. The review is focused on superconducting FCL made of AC superconducting wires. Second, the experimental evaluation of the new superconducting FCL which has been developed by Tokyo Electric Power Co. and Toshiba Corporation is described. The success of the current suppression up to 1, 800A is emphasized.
Structural metallic materials in cryogenic engineering relating with superconducting magnets are generally used under high magnetic field and stress. However, only a few researches on cryogenic structural metallic materials have taken into consideration the effects of magnetic field on mechanical and other properties. The reason for this fact is mainly due to the lack of experimental data about the effects. It is very important to make clear the effects in order to develop widely and soundly cryogenic and superconducting technologies. In the present article, several subjects relating with the effects of magnetic field on mechanical properties, martensitic transformation and other properties mainly at cryogenic temperatures are reviewed.
High cycle fatigue tests at cryogenic temperatures were performed for titanium alloys and austenitic steels. The S-N curves shifted to higher stress or longer life side with a decrease in test temperature with some exceptions in forged Ti-6Al-4V alloys. There was little change in fatigue strength between 77K and 4K for the forged Ti-6Al-4V alloys. Fatigue strength at 106 cycles increased in proportion to a gain in strength by temperature decrease. However, a ratio of the farigue strength to tensile or yield strength depended on material and its processing. From the viewpoint of combination of yield strength and fatigue strength, austenitic steels had a higher fatigue strength than titanium alloys at a given yield strength. Among the titanium alloys, the rolled ones exceeded the forged ones.