[APP2] Magnets, Electric power devices, Rotating machines

[APP2-14] Experimental Evaluation of Current Distribution on Transposed Four-Parallel Conductors in Three-phase REBCO Armature Coils under Rotating Magnetic Field

*Yudai Kimura¹, Goki Kawasaki⁴, Masayuki Ishihara¹, Tomohiro Inoue¹, Kohei Yoshida¹, Shun Miura³, Hiroshi Miyazaki¹, Akifumi Kawagoe², Masataka Iwakuma¹ (1. Kyushu Univ. (Japan), 2. Kagoshima Univ. (Japan), 3. NIFS (Japan), 4. NIT, Miyakonojo C (Japan))

Keywords:

Fully Superconducting Motor,Armature Coil,Transposition,Current Distribution,Uniform Current,Circulating Current

Fully superconducting rotating machines employing superconducting armature and field coils are highly attractive for aircraft applications due to their high-power density. Since practical superconducting motors are expected to involve large transport currents in the armature, we have developed a cabling design for the transposed multi-strand parallel conductors. In general, introducing more transpositions into a coil leads to a more uniform current distribution. However, this significantly reduces the manufacturability of coil and increases the cost and size. Therefore, it is necessary to find a transposition configuration that minimizes the number of transpositions as much as possible and provides uniform current distribution. We have previously proposed the transposition concept to suppress the nonuniform current distribution among strands caused by inductance irregularities between each strand in armature windings¹⁾²⁾³⁾. We found that circulating currents in the armature windings, induced by the magnetic flux variations of the rotor, also have a significant impact on the current distribution in actual motor environments and lead to a reduction in output. Therefore, this study aims to develop a transposition method that reduces the inductance irregularities from the armature and circulating currents induced by the rotor. We fabricated the test coils composed of four-strand REBCO parallel conductors and proposed a novel transposition method. This method is based on the CUCG¹⁾ which can reduce inductance irregularities among four-parallel conductors and achieve the uniform current branch under single-phase coil conditions. In addition, we improved the end-turns section of the transposition so that the coil can flip, thereby reducing the effects of the magnetic flux variations of the rotor. The FEM calculations were conducted by applying a 50 A, 10 Hz current to the armature under a magnetic flux density of 0.4 T at the surface of the field magnets, with the system modeled as a synchronous motor using a novel transposition. The calculations were performed for load angles of 0°, 45°, and 90°. The analysis showed a uniform current distribution in three-phase armature coils under rotating magnetic field even in case of large load angles. The obtained current distributions of each strand were 25.05%, 24.95%, 25.01% and 24.99%. The next step is to experimentally verify the uniform current distribution of this coil under a rotating magnetic field condition. The armature windings, consisting of six racetrack coils applying a novel method, are energized with three-phase alternating current under a 0.4 T neodymium-magnet field, and the measurements were performed at liquid nitrogen temperature (77 K). The current in each strand is measured while the system operated as a synchronous motor. The frequency of the applied current was gradually increased until the rotor lost synchronism. Rogowski coils are used for measuring current in each strand, with the induced voltage waveforms recorded. In addition, the total current of each phase is measured as a voltage waveform using shunt resistor. The experimental results and influence of a rotating magnetic field on the current distribution will be discussed in ISS 2025.
Presentation Materials
https://iss-archives.jp/iss2025.jp/slides/APP2-14.pdf