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We have proposed a superconducting thin-film fault current limiter (FCL) that uses high-resistivity Au-Ag alloy shunt layers for the protection against "hot spots". Its design enables reduction of the total length of FCL elements that can withstand high electric fields 40 V peak cm, thus greatly reducing the cost of FCLs. In this paper, two methods to increase current capacity of the FCLs were demonstrated. The first method protects the films from hot spots by using capacitors in addition to external resistors. The capacitors decrease rapid voltage rise in the films at the moment of quenching. The second method maximizes the rated current of two parallel-connected thin films by using parallel connections via superconducting tapes, even if the critical currents of these films are largely different. We then successfully tested two parallel-connected YBCO films prepared by a low-cost, metal organic deposition (MOD) method. Over-current tests showed that (a) superconducting transport currents up to 380 A peak flowed 5 cycles without quenching, which is more than 1.3 times larger than the peak value of the 200 A rms rated current and (b) after switching, = 45 7 V peak cm was achieved without film degra- dation.Index Terms-Au-Ag alloy shunt layers, current capacity, electric fields, fault current limiters, YBCO thin films.

Stabilities o f magnets in a h i g h gravitational field up t o 2000 G are discussed, based upon the experimental results o f forced quench t e s t s in a set o f rotating magnets, in order to establish the s t a b i l i t y design criterion o f field windings o f superconducting generators. R e l a t i o n s o f propagat i o n v e l o c i t i e s , recovery currents, minimum quench energy and heat transfer characteristics are studied, a g o o d agreement between the experimental results and a theory confirmed the improvement o f magnet s t a b i l i t y in a h i g h gravitational field because o f the enhanced heat transfer characteristics.Superconducting power generators are being developed in Japan, as a part of a R&D program on energy technology, the New Sunshine Project. In this development, national laboratories are taking a role of fundamental studies to contribute to the K&D being carried out mainly by the manufacturers involved in a research association, Super-GM. The stability design criteria of field windings is the issue of great importance to be clarified, because extremely high reliability is required not only for the safety but to ensure the operation of power generators free of troubles. The possibility of both of degradation and improvement of the stability of magnets is considered in a high gravitational field. Because the strong centrifugal force may deform the coil structure and generate friction loss in the wires of magnets, but the cooling characteristics by natural convection will be enhanced at the same time. It is our purpose to evaluate these effects quantitatively, and to establish the scaling law of the stability design criteria of field windings in a high gravitational field.

The transformer type superconducting fault current limiter, which is made up of a series transformer and a superconducting current limiting device, has many advantages such as the design flexibility of the current limiting device. However, the design strategy for determining the superconducting current limiting device ratings and the transformer ratings is unclear because the relations between the current limiting characteristics and these ratings are not analyzed enough.In this paper, the relations between the current limiting characteristics and these ratings are analyzed theoretically. The experimental results of the transformer type superconducting fault current limiter are also shown.