There has been a worldwide rush to solve environmental and energy problems in recent years. In particular, the development of high-efficiency, high-power-density rotating machines has been active in the transportation and energy fields. Fully superconducting rotating machines (FSRMs), which have superconducting field and armature windings [1] attract attention because they achieve high efficiency and high-power density. We have been studying the FSRM using REBCO wire for the field windings and MgB2 wire for the armature windings [2].
AC losses, hysteresis and coupling losses, are generated because a rotating magnetic field is applied to the armature windings. It is very important to develop a FSRM to investigate the magnitude and causes of this AC loss in detail. Therefore, we have experimentally measured the AC loss in MgB2. Figure 1 shows the AC loss measurement equipment based on mechanical input. MgB2 coil is placed inside the cryostat. A rotating magnetic field is applied to the MgB2 coil by rotating a Halbach array of permanent magnets outside the cryostat. Temperature sensors are attached to the MgB2 coil so that we can measure the temperature at some parts of the MgB2 coil. It is necessary to consider the electromagnetic phenomena and heat generation by AC losses in the measurement equipment.
This study aims to improve measurement accuracy by a detailed understanding of electromagnetic and thermal conduction phenomena in AC loss measurement equipment based on mechanical input. We use multiple temperature sensors to evaluate the temperature distribution. By comparing two types of wire with the same diameter, number of filaments, and filament diameter but different twist pitches (25 mm and 100 mm), the relationship between the magnitude of AC loss and temperature gradient due to twist pitch is clarified.
[1] Yutaka Terao, Satsuki Okumura, Hiroyuki Ohsaki, “Study on Electric and Magnetic Loadings in Fully Superconducting Motor Design,” Physica C: Superconductivity and its Applications, vol. 617, 1354399, 2024.
[2] Yutaka Terao, Haruka Nakamura, Satsuki Okumura, Shuichiro Fuchino, Hiroyuki Ohsaki, “AC Loss of MgB2 Superconducting Coils with Alternating Transport Current in Rotating magnetic Field,” IEEE Transactions on Applied Superconductivity, vol. 33, no. 5, pp. 1-5, Aug. 2023.
Figure 1. The AC loss measurement equipment based on mechanical input
Keywords: MgB2, AC loss, thermal conduction phenomena