Charge–Discharge and Thermal–Electrical Characteristics of GdBCO Coils Wound With Various Types of Grease as an Insulation Material

Kim, Seonggyeom; Choi, Yoon Hyuck; Yang, Dong; Kim, Young Gyun; Lee, Haigun

doi:10.1109/tasc.2016.2530747

Cited by 20 publications

(6 citation statements)

References 17 publications

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“…HE stability of rare-earth barium copper oxide (REBCO) pancake coils is drastically enhanced with a no-insulation (NI) winding technique [1]. Following the NI winding technique, some methods of increasing the REBCO magnet stability have been proposed; a metal insulation technique [2], [3], a metal cladding [4], the use of thermal grease [5], a smart switching by metal-insulator transition (MIT) [6], and a coating with electrically conductive epoxy resin [7]. A key of these techniques is the increase in the contact resistance.…”

Section: Introductionmentioning

confidence: 99%

Turn-to-Turn Contact Resistance Measurement of No-Insulation REBCO Pancake Coil: External Field Dependence

Noguchi

Mori²,

Mato³

et al. 2021

IEEE Trans. Appl. Supercond.

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The characteristics of no-insulation hightemperature superconducting (HTS) manet is dominated by the magnitude of the turn-to-turn contact resistance. A few techniques have been proposed to increase the turn-to-turn contact resistance. The relation between the turn-to-turn contact resistance and the magnet stability has also been investigated in simulations. Although the turn-to-turn contact resistance measurement was only the sudden-discharging method before, we proposed a lowfrequency-AC current (LFAC) method. Using our proposed method, it is possible to measure the turn-to-turn contact resistance under various conditions. In a previous paper, we measured it when charging DC current to a single pancake coil. In this paper, the turn-to-turn contact resistance was measured by the LFAC method when an external field of 1-3 T was applied to a single pancake coil. The coil strain was also measured, and the relation of the turn-to-turn contact resistance and the coil strain was also discussed.

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Section: Introductionmentioning

confidence: 99%

Turn-to-Turn Contact Resistance Measurement of No-Insulation REBCO Pancake Coil: External Field Dependence

Noguchi

Mori²,

Mato³

et al. 2021

IEEE Trans. Appl. Supercond.

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“…On the other hand, to mitigate the long charging delay drawback, a few techniques have been proposed, e.g. use of thermal grease [9] and a metal-as-insulation (MI) technique [10]. The key aim of these techniques is to increase turn-to-turn contact resistivity, while without losing the self-protecting feature.…”

Section: Introductionmentioning

confidence: 99%

A simple protection evaluation method for no-insulation REBCO pancake coils during local normal-state transition

Noguchi

Hahn

Ishiyama

et al. 2019

Supercond. Sci. Technol.

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No-insulation (NI) and metal-insulation (MI) winding techniques are promising for enhancing the thermal stability of REBCO pancake coils, toward the practical use of nuclear magnetic resonance and magnetic resonance imaging systems. The NI and MI REBCO pancake coils showed high thermal stability in many over-current tests. However, a disadvantage is a charging delay due to low turn-to-turn contact resistance. Therefore, many researchers have tried to increase turn-to-turn contact resistance to overcome the charging delay problem. Meanwhile, a partial element equivalent circuit (PEEC) model can accurately simulate the over-current and charging/discharging tests of NI REBCO pancake coils in detail. Using the PEEC model coupling with thermal finite element analysis (FEA), the thermal stability was evaluated during a local normal-state transition. From the simulation results, it was found that a best range of turn-to-turn contact resistance existed to keep a high thermal stability during a local normal-state transition. However, the PEEC and thermal FEA method requires a substantial amount of time with complicated simulation approach. In this paper, we propose a simple mathematical formulation to obtain an appropriate range of turn-to-turn contact resistance during a local normal-state transition, supposing a worst cooling condition. The simple computation is easy to use and timesaving to roughly estimate the operation reliability of NI REBCO pancake coils.

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“…The no-insulation (NI) high temperature superconductor (HTS) pancake winding technique is expected to provide a practical solution for stability and protection of HTS magnets, and it has been regarded as a promising approach to build high field HTS direct current (DC) user magnets [1]. To date, >13 NI HTS magnets, mostly made of REBCO tapes, have been built and tested [2][3][4][5][6][7][8][9][10], including the 26 T 35 mm in inner diameter (35 mm) all-REBCO magnet completed in 2015 [11]. More NI REBCO magnets are currently being built, which include: (1)13T 58mm insert for a 20 T allsuperconducting magnet system by the National High Magnetic Field Laboratory (NHMFL), which will be, upon successful completion in early 2017, the first DC user magnet with the NI technology incorporated; (2) 800 MHz (18.8 T) 91 mm insert coils for 1.3 GHz low temperature superconductor (LTS)/HTS nuclear magnetic resonance (NMR) magnet by the Francis Bitter Magnet Laboratory, MIT; (3) 10 T 125 mm insert for 30 T DC user magnet by the Laboratoire National des Champs Magnétiques Intenses Grenoble; (4) 400 MHz 64 mm all-REBCO NMR magnet by a team from the Korea Basic Science Institute (KBSI), the National High Magnetic Field Laboratory (NHMFL), SuNAM Co. Ltd., the Korea Institute of Machinery & Materials, and Kunsan National University [12].…”

Section: Introductionmentioning

confidence: 99%

Design and performance estimation of a 35 T 40 mm no-insulation all-REBCO user magnet

Kim

Bhattarai

Jang

et al. 2017

Supercond. Sci. Technol.

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This paper presents a design of a 35 T 40 mm winding diameter no-insulation standalone magnet that consists of a stack of 52 double pancake (DP) coils wound with multi-width REBCO tapes. The inner and outer diameters and height of the magnet are 40 mm, 221.6 mm, and 628 mm, respectively. It is designed to generate 35 T at an operating current (Iop) of 179.8 A in a bath of liquid helium at 4.2 K. All the DP coils will be ‘dry’ wound without epoxy, making turns within the DP coils to be essentially ‘self-supporting,’ which is effective to reduce the magnetic stress. To reduce the magnet charging time constant, the so-called ‘metallic cladding’ REBCO tapes will be adopted, where a 1–2 μm thick stainless steel layer surrounds the tapes hermetically. With an average surface contact resistance (Rct) of 170 cm−2, experimentally obtained from a charging test of our recent 3 T 100 mm stainless steel cladding REBCO magnet, the charging time constant of the 35 T magnet was estimated to be 3.01 minutes, though the magnet will be energized substantially slower over a few hours to reduce ac loss and Joule heating from radial turn-to-turn leak currents. A preliminary post-quench analysis, based on our lumped equivalent circuit model, was performed; the total stored energy of 1.79 MJ (magnet inductance: 110.5 H) was expected to be discharged in approximately 1.28 seconds after a quench due to the fast electromagnetic quench propagation among the DP coils, while the peak hot spot temperature was estimated to rise to 94 K, acceptable for a safe quench of a REBCO magnet.

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Charge–Discharge and Thermal–Electrical Characteristics of GdBCO Coils Wound With Various Types of Grease as an Insulation Material

Cited by 20 publications

References 17 publications

Turn-to-Turn Contact Resistance Measurement of No-Insulation REBCO Pancake Coil: External Field Dependence

Turn-to-Turn Contact Resistance Measurement of No-Insulation REBCO Pancake Coil: External Field Dependence

A simple protection evaluation method for no-insulation REBCO pancake coils during local normal-state transition

Design and performance estimation of a 35 T 40 mm no-insulation all-REBCO user magnet

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