Transient voltages and energy balance in REBCO insulated magnet: experimental and numerical studies

Tixador

2022

Self Cite

In the framework of the BOSSE project, a 12 T insulated REBCO solenoid is being manufactured. This magnet will be used as a SMES with the objective to reach 1 MJ and a specific energy of 20 kJ/kg for the winding. To manufacture this solenoid and reach such performances, 21 insulated REBCO Double Pancakes (DPs) will be assembled and cooled in a liquid helium bath at 4.2 K. To validate the solenoid's electromagnetic design, a prototype DP tested in self-field up to its critical current (972 A), thanks to a sensitive protection system, was presented in a previous work. Here we present the background magnetic field test of this prototype DP which allowed to validate the coil's mechanical design. In order to validate the electromagnetic performances of the 21 DPs, each of them is tested in liquid helium up to its rated current. The performances of the 17 DPs already tested and validated will also be presented. Finally, we will present the tests and results of 2 preliminary assemblies of 3 and 5 DPs. These assemblies were tested with two different protection philosophies. The results of these tests show that an individual protection of each DP is to be preferred in order to obtain a better sensitivity on the protection signal.

Section: A Assembly Characteristics and Test Resultsmentioning

confidence: 89%

Section: Protection Of Dps In Assembliesmentioning

confidence: 99%

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12 T Insulated REBCO Magnet Used as 1 MJ SMES: Protection Strategies and Preliminary Assembly Tests

Vialle

Tixador

2022

Self Cite

“…7). This high radial stress and strain value illustrate the fact that the turns are not glued together, as such stress would surely cause delamination [11], and that radial stress is solely applied to the flanges.…”

Section: Measured Strain and Discussionmentioning

confidence: 99%

A High Performance Insulated REBCO Pancake With Conductive Cooling Capability

Vialle

Takahashi

et al. 2023

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REBCO Coated Conductors have high tensile strength along their length. They are however sensitive to delamination when traction force is applied on the tape surface, which in a pancake winding corresponds to radial tensile stress. For this reason, most REBCO magnets are dry-wound (not impregnated). One of the drawbacks of dry winding is that conduction cooling to low temperature (below 20 K) would be inefficient. Edge impregnation structures were developed to mitigate this problem but retaining a soft non-stick insulating layer in between the turn. In this paper, we propose an improved pancake structure with the benefits of edgeimpregnation but using Hastelloy tape with thin insulation coating to reinforce the winding. The mechanical behavior of such structure is first estimated then validated with high current tests under large background magnetic field. The insulation performance is then tested by rapid ramping and fast discharge.

“…In [8] it was estimated through detailed thermos-electric modelling that even though the thermal runaway itself occurs too fast for protecting the coil using a dump resistor, the dissipation levels are measurable (in the 1 -10 mV range in the current density range we are using here) a few seconds before, time enough to initiate a preemptive discharge preventing the thermal runaway to occur. The challenge is then to discriminate this dissipative signal from the other transient signals across the coil as discussed first in [18] and more in details in [19]. Moreover, it is important to be able to localize an eventual dissipative area so that the faulty pancake can be replaced without damage to the other pancakes.…”

Section: A Robust Rebco Coil Protection Conceptmentioning

confidence: 99%

First Validation of Robust REBCO Insert Concept on a Large 20-Pancake Prototype Reaching Up to 25 T

Takahashi

Zampa

et al. 2023

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We recently proposed a robust REBCO insert coil concept in the framework of a project to upgrade the 25 T CSM magnet at HFLSM with a new REBCO insert to reach 30 T. In this concept, the conductor consists of a two-tape bundle to mitigate the risks posed by local tape degradation. So-called edge impregnation is used to enhance the mechanical stiffness while reducing delamination risk, providing conduction-cooling capability at the same time. This insert is to be protected against the risk of thermal runaway simply by using dump resistor, thanks to an early detection concept. The different ideas forming the robust REBCO insert coil concept were tested successfully on various small scale prototypes. We report here their first implementation on a large-size insert coil, consisting of 20 stacked pancakes from the 30 T CSM upgrade insert. The mechanical behavior of the coil is modelled and validated with experiments. The thermal runaway detection setup is introduced. Its sensitivity and selectivity is discussed based on previous works on thermal runaway scenarios.