Nb3Sn/NbTi superconducting windings for 30 MVA synchronous rotary condenser

This paper is concerned with the construction and the test of superconducting coils for the field of a 30 MVA synchronous rotary condenser. The superconducting field is a dipole magnet which consists of 8 coils. Two coils are made of Nb3Sn monolithic conductors. Another six coils are made of NbTi monolithic conductors. The heat treatment of Nb3Sn conductors was made after winding (Wind and React). Coils were inserted into slots of a rotor and were fixed by wedges. Both conductors (NbTi, Nb3Sn) are insulated by the helical wrap of insulation tapes. Thus, the conductors are directly cooled by liquid He. Superconducting coils were assembled into a rotor; the rotor was made of Ti and Ti alloy. The rotor was rotated up to 3900 r.p.m. (108% over speed) for a rotor balancing, the maximum centrifugal force being up to 4200g (g; gravity). Then, the rotor was cooled down and the field winding was energized in liquid He. It was found that the degradation due to the rotation did not occur in Nb3Sn coils. The field winding could be energized up to 1007A. By the way, the operational current of the field winding in a 30 MVA machine is 770A.