Design and first stage test of 50-meter flexible superconducting cable

A 50-meter flexible superconducting cable model is described, including a copper-stabilized Nb3Sn-tape current-carrying core and cable-paper electric insulation of 13 mm total thickness which is submerged in cold helium while under working conditions. The helium-cooled inner channel is 36 mm in diameter and the outer diameter of the current-carrying core is 75 mm. Helium also flows in an annular channel between the outer surface of the core and a corrugated enclosure. The core is incorporated in a flexible cryostating envelope consisting of 4 corrugated enclosures; the two middle pipes form an annular channel for liquid nitrogen which reduces heat leaks to helium. The design of a 110 kV, 12 kA lead was developed to test the flexible superconducting cable model. For d.c. and a.c. tests of the model, a technique of inductive current introduction through a superconducting transformer is offered. A multisection transformer with a superconducting primary of insulated Nb3Sn tape was manufactured, the current-carrying core being the secondary. Before assemblying, the sections were tested in a liquid helium cryostat to check the design characteristics and to determine the critical current in the winding. A.C. losses (50 Hz) in the transformer´s primary were measured. The cable model was cooled by two improved helium refrigerator plants, HGU-150/4,5. Current tests were performed at a working temperature.