Power transformers with superconducting windings need a protection system to prevent damage to the low-loss superconducting winding by an abnormally high current. The generally accepted protection technique which uses auxiliary coils has been analysed using a network representation. The current distribution between main and auxiliary coil is expressed in terms of geometrical parameters. Experimental data on current transfer and main coil recovery in a test transformer are presented and a method of obtaining a very low auxiliary coil current is suggested.

Recent studies1I2 confirm the economical feasibility of the .application of superconductors in AC power apparatus. The low-loss conductor which has been proposed still only exists in theory. Simple calculations show that the economic criterion described by Ogasawara3 and Hldsnik' is inaccurate because of an oversimplified hysteresis loss formula. A necessary modification shows that stricter demands will have to be made. As production of ultrafine filaments is abig technological problem, final diameter reduction by rolling instead of drawing is proposed. The expected better performance of a rolled composite has been verified experimentally in test coils as well as in transform&-geometry. Experimental setup and results are presented.