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.
van Overbeeke, F., Oordt, K., & van de Klundert, L. J. M. (1985). Design and operation of a protection system for transformers with superconducting windings. Cryogenics, 25(12), 687-694. https://doi.org/10.1016/0011-2275(85)90189-4