Motors Employing REBCO CORC and MgB₂ Superconductors for AC Stator Windings

Future all-electric aircraft will employ highly efficient compact and lightweight machines for power generation and propulsion applications. Previous studies have indicated that the most attractive options include synchronous machines employing superconducting excitation and stator windings for achieving high power density and efficiency. The dc excitation winding could be constructed using a variety of superconductors, but the choice for ac stator windings is limited. High conductivity aluminum conductor at cryogenic temperature is a possible option but it is expected to be heavier than a superconducting winding and will require more extensive cooling as the losses within the winding pack will be much larger. A conductor-on-round-core (CORC) cable using REBCO tapes looks like an attractive option as it enables compound bending for constructing saddle coils. Here, we investigate using this cable for the stator winding of a 3 MW, 4500 RPM, 4-pole propulsion motor and compare with an identical motor employing an MgB ₂ stator winding. The motor configuration assumes saddle-shaped coils for the stator winding. Each saddle coil constitutes a double pancake. A round conductor capable of bending in three-dimensional is preferred for such coils, making the round CORC cable ideal for this application. The cable employs striated REBCO with striation width as small as 1/3 mm. The ac field in the stator winding region is about 0.7 T at 150 Hz and the cable is operated at 50% of its critical current for limiting ac losses and for providing a safety margin. Individual tapes in the CORC cable experience field perpendicular to its broad face resulting in high ac losses. Comparing the performance of motors employing CORC and MgB ₂ cables for the stator, we find that the ac losses in the CORC stator are much larger than the MgB ₂ stator. High losses in the CORC stator winding make this option less attractive unless coolant power is freely available, such as in LH ₂ -fueled planes. However, this machine with CORC coils is the most compact and lightweight option. Such compact light mass motors could be attractive for LH ₂ fueled applications, such as interstate trucks, heavy machinery, locomotive hauling goods trains, ships (especially for podded propellers), etc.