Normal zone propagation characteristics of coated conductor according to insulation materials

Yang, Seong Eun; Ahn, Min-Cheol; Park, D.K.; Chang, Ki Sung; Bae, Duck Kweon; Ko, Tae Kuk

doi:10.1016/j.physc.2007.04.308

Cited by 5 publications

(4 citation statements)

References 2 publications

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“…The same factors that suppress quench occurrence would now result in a very slow development of the thermal instability and inhibit its propagation along the wire. The normal zone propagation velocity reported [3,4] for practical 2G superconductor wires is in the range of 0.1-1 cm s −1 , which is 10 3 -10 4 times less than in the low-T c materials. Slow developing thermal instability means that a small local hotspot is initially formed in the wire and some significant heating occurs there prior to the surrounding region quenching into the normal state.…”

Section: Introductionmentioning

confidence: 85%

Quench detection method for 2G HTS wire

Marchevsky

Xie²,

Selvamanickam

2010

Supercond. Sci. Technol.

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2G HTS conductors are increasingly used in various commercial applications and their thermal and electrical stability is an important reliability factor. Detection and prevention of quenches in 2G wire-based cables and solenoids has proven to be a difficult engineering task. This is largely due to a very slow normal zone propagation in coated conductors that leads to formation of localized hotspots while the rest of the conductor remains in the superconducting state. We propose an original method of quench and hotspot detection for 2G wires and coils that is based upon local magnetic sensing and takes advantage of 2G wire planar geometry. We demonstrate our technique experimentally and show that its sensitivity is superior to the known voltage detection scheme. A unique feature of the method is its capability to remotely detect instant degradation of the wire critical current even before a normal zone is developed within the conductor. Various modifications of the method applicable to practical device configurations are discussed.

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Section: Introductionmentioning

confidence: 85%

Quench detection method for 2G HTS wire

Marchevsky

Xie²,

Selvamanickam

2010

Supercond. Sci. Technol.

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“…Thermal gradients for Coil C are shown in Figure 14 (again, T p = T h -T 0 ). Using again Eq (9) and the data in Figure 14 we obtained an average thermal conductivity of the winding of Coil C as <κ>=2.35 Wm -1 K -1 . Here we took the gradient from the steepest portion of the curve, that between T1-T2, assuming at this low level of excitation the heat is removed by the T3 layer.…”

Section: Thermal Gradient Measurements Of Coil C (12 M/45 Turns Zno mentioning

confidence: 99%

“…Figure 8(b) shows the temperature gradient at two different power levels. We again can use Eq (9) to extract κ, obtaining κ = 2.79 Wm -1 K -1 .…”

Section: Thermal Gradient Measurements Of Coil B (1 M/4 Turns Zno Ins...mentioning

confidence: 99%

“…Another alternative is the use of a thin sol-gel type insulation, similar to that used for Bi-2212 [8], bearing in mind that those of Ref [8] tend to stick best to Ag surfaces. But presently, researchers looking at YBCO for magnet applications tend to use Mylar or similar insulation -even if noting the need for better thermal conductivity [9]. Below we will investigate both quench propagation in small pancake coils made with coated conductor and the differences seen with different insulations methods.…”

Section: Introductionmentioning

confidence: 99%

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Thermal diffusion and quench propagation in YBCO pancake coils wound with ZnO and Mylar insulations

Sumption

Majoroš

Susner

et al. 2010

Supercond. Sci. Technol.

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The thermal diffusion properties of several different kinds of YBCO insulations and the quench properties of pancake coils made using these insulations were studied. Insulations investigated include Nomex, Kapton, and Mylar, as well as insulations based on ZnO, Zn 2 GeO 4 , and ZnO-Cu. Nomex, Kapton, and Mylar, chosen for their availability and ease of use, were obtained as thin ribbons, while the ZnO based insulations were chosen for their high thermal conductivity and were applied by a thin film technique. Initially, short stacks of YBCO conductors with interlayer insulation, epoxy, and a central heater strip were made and later measured for thermal conductivity in liquid nitrogen. Subsequently, three different pancake coils were made. The first two were smaller, each using one meter total of YBCO tape present as four turns around a G-10 former. One of these smaller coils used Mylar insulation co-wound with the YBCO tape, the other used YBCO tape onto which ZnO based insulation had been deposited.One larger coil was made which used 12 total meters of ZnO-insulated tape and had 45 turns.Temperature gradients were measured and thermal conductivities were estimated from these coils, the results obtained were compared to those of the short stacks. The results for all short 2 sample and coil thermal conductivities were ~1-3 Wm -1 K -1 . The lack of distinction for the ZnObased insulations was attributed to the presence of a thermal interface contact resistance. TheZnO insulations, while not strongly increasing the average thermal conductivity of the winding pack or coil, were much thinner than the other insulations, and would thus enable substantial increases in winding pack critical current density. Finally, quench propagation velocity measurements were performed on the coils (77 K, self field) by applying a DC current and then using a heater pulse to initiate a quench. Normal zone propagation velocity (NZP) values were obtained for the coils both in the radial direction and in the azimuthal direction. Radial NZP values (0.05-0.7 mm/s) were two orders of magnitude lower than axial values (~14-17 mm/s).Nevertheless, the quenches were generally seen to propagate radially within the coils, in the sense that any given layer in the coil is driven normal by the layer underneath it. This initially surprising result is due to the fact that while the radial normal zone propagation velocity (NZP) is much lower than the NZP along the conductor (∼100 x) the distance the normal zone must expand longitudinally is much larger than what it must expand radially to reach the same point, in our case this ratio is ~ 1600.Keywords: YBCO, Coated conductor, Quench, Stability, thermal conductivity varied; sometimes they were performed in vacuum, or more frequently under gas cooling. More recently, results for quench measurements of small coils of YBCO are becoming available [6,7], although much work remains to be done. Of course, as it was for other magnet/conductor systems, insulation is very important. One of the key issues is ...

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Epoxy-based thermally conductive adhesives with effective alumina and boron nitride for superconducting magnet

Hwang

Kim

et al. 2020

Composites Science and Technology

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Normal zone propagation characteristics of coated conductor according to insulation materials

Cited by 5 publications

References 2 publications

Quench detection method for 2G HTS wire

Quench detection method for 2G HTS wire

Thermal diffusion and quench propagation in YBCO pancake coils wound with ZnO and Mylar insulations

Epoxy-based thermally conductive adhesives with effective alumina and boron nitride for superconducting magnet

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