Design, Fabrication, and Critical Current Testing of No-Insulation Superconducting Rotor Coils for NASA's 1.4 MW High-Efficiency Megawatt Motor

Abstract

NASA Glenn Research Center is developing a 1.4 MW high-efficiency electric machine for future electrified aircraft to reduce energy consumption, emissions, and noise. This wound-field, synchronous machine employs a self-cooled, superconducting rotor to achieve excellent specific power and efficiency. This paper discusses the design and fabrication of the no-insulation high temperature superconducting (HTS) rotor coils and compares them to conventionally insulated HTS coils. Two sub-scale test coils with epoxy on only one axial face were fabricated. Critical current testing of the coils at 77 K and self field was conducted to study the influence of thermal cycling on their critical current and n-value. After two or four aggressive thermal cycles between 77 K and about 278 K (5 • C), the critical current and n-value were nearly unchanged, indicating very little to no degradation.

Progress Toward the Critical Design of the Superconducting Rotor for NASA's 1.4~MW High-Efficiency Electric Machine

“…The preliminary design of the HEMM's superconducting rotor was detailed in [12] and [13]. Figure 1 depicts the current design of the superconducting rotor and Table 1 summarizes the notable characteristics.…”

“…Although they were suggested only recently, a number of papers have reported the fabrication and critical current testing of no-insulation coils [13,14,16,17]. However, no-insulation coils have not been used in the rotor of an electric machine.…”

“…To reduce the risk that the HEMM's superconducting coils will be damaged by thermal stresses, a series of thermal cycling tests have been conducted on multiple sub-scale test coils. Prior work by the authors [13] discussed the coil fabrication and testing procedures and presented initial measurements of how two small, single-layer coils responded to repeated thermal cycling between room temperature and liquid nitrogen temperature (77 K). Here, that work is expanded by describing an improved coil fabrication procedure and by presenting thermal cycling measurements of two new sub-scale coils that have nearly all of the features of the full-scale HEMM coils.…”

“…After winding multiple sub-scale HTS coils using the authors' original coil fabrication process [13], the process was found to have a few deficiencies. The primary issue was that the geometry of the coils' end turns considerably deviated from the design; this resulted from the coil former's insufficient stiffness in some locations and the build up of a small amount of slack in the coil while winding.…”

“…The testing procedure was the same as described in [13] except in the following ways. Here, the coils were given several minutes more time to warm up and were also given five minutes to cool down.…”