Contact Resistance and Current Characteristics of NI HTS Coils in Low Frequency AC Method

The development of high-performance HTS magnets requires a method to correctly measure the contact resistance between turns of no-insulation (NI) coils. We have proposed a method to measure the turn-to-turn contact resistance of NI coils using low frequency alternating current (LFAC). In the LFAC me...

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Bibliographic Details
Published in:IEEE transactions on applied superconductivity 2023-08, Vol.33 (5), p.1-5
Main Authors: Kim, SeokBeom, Kobayashi, Hirotaka, Sato, Daiki, Inoue, Ryota, Ueda, Hiroshi, Mato, Takanobu, Noguchi, So
Format: Article
Language:English
Subjects:
Alternating current
Coils
Coils (windings)
Contact resistance
Cooling
Current distribution
Current measurement
Electrical resistance measurement
High-temperature superconductors
LFAC method
Liquid nitrogen
Low frequencies
Magnets
Measurement methods
NI HTS coil
Nonuniformity
Pickup coils
Reliability analysis
Spatial resolution
turn-to-turn contact resistance
Windings
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Summary:The development of high-performance HTS magnets requires a method to correctly measure the contact resistance between turns of no-insulation (NI) coils. We have proposed a method to measure the turn-to-turn contact resistance of NI coils using low frequency alternating current (LFAC). In the LFAC method, AC current is used, and it is assumed that all the AC current flows in the radial direction of the NI HTS coil. To confirm the reliability of the proposed measurement method, AC current distribution characteristics were evaluated using four (quarter circle, 1/4 size) pickup coils in a previous study. The pickup coils were mounted under the NI test coils and the current bypass characteristics from circumferential to radial direction were evaluated as a function of frequency. However, the size of the fabricated four pickup coils was relatively large compared to the test coil, so its sensitivity and spatial resolution were not sufficient. Therefore, in this article, we prepared eight pickup coils smaller than the 1/4 size pickup coil used in the previous study. Two test coils with winding tensions of 0.5 and 1 kg were prepared, and the non-uniformity of the contact resistance of both NI coils was detected using eight pickup coils.**We also identified locations in the test coil where the contact resistance changed due to multiple cooling cycles by liquid nitrogen.
ISSN:1051-8223
1558-2515
DOI:10.1109/TASC.2023.3248519