Design of 2-MW REBCO Fully Superconducting Synchronous Generator With Saddle-Shaped Field Coils and Distributed Armature Windings

To achieve carbon neutrality in the aviation sector, significant efforts to develop electric propulsion systems for aircraft are underway. These systems require high-power-density equipment, particularly propulsion drivetrains. In this light, the development of a 2-MW electric propulsion system that incorporates a fully superconducting generator and motor is underway. This paper presents the electromagnetic design and key features of the 2-MW fully superconducting synchronous generator using REBa<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>Cu<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub>O<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-δ</sub> (REBCO) tapes. The generator is designed as a two-pole machine operating at 3,600 rpm. To ensure mechanical integrity at high rotational speeds, a highstiffness through-shaft was implemented, and saddle-shaped windings were selected for the field coil. The coil ends were optimized using the generalized Frenet–Serret equations, effectively minimizing their length and mitigating critical current degradation in the REBCO tape. Furthermore, a face-toface double-stacked (FFDS) REBCO tape—known for its superior strain tolerance—was employed. Under an operating current of 230 A DC, the field coil achieved a maximum magnetic field of 1.6 T, with a load factor estimated at 87% at 65 K. The armature winding features a novel distributed winding scheme, wherein the U, V, and W phases overlap by 60° through a variation in winding radius. Each winding comprises 20 stacked FFDS REBCO tapes, with reversed tape positions between adjacent turns to ensure uniform current distribution. The design ensured that the load factor remained below 100%, even at an armature temperature of 77 K. To reduce the overall weight of the generator, the back iron yoke was eliminated, and the armature casing was constructed from the glass-fiberreinforced plastic. A 0.9 W resistive load was connected to the armature, and three-dimensional electromagnetic analyses were conducted. The effective armature current and line voltage were calculated to be 881 A<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rms</sub> and 1374 V<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rms</sub>, respectively, corresponding to an estimated output power of approximately 2.1 MW.