Mechanical Analysis of a No-insulation Pancake Coil with the Overband During a Quench

The experiments have showed that the actual value of magnetic field in the magnet wound by rare-earth (RE) Ba2Cu3O7−x (REBCO) tape during the operation is less than its design value due to the effect of screening current-induced magnetic field (SCMF). Some simulation methods have been used to calculate the SCMF. In this paper, a modified model is proposed to estimate the SCMF of the magnet based on the previous simple model. The inductance correction and field-dependent critical current density are considered in the modified model. Thereinto, two parameters, named reversal coefficient and Nagaoka coefficient, are introduced in the model. The former is used to track the location of the minimum SCMF value in the charging process, and the latter is applied to correct the induction of the magnet. The numerical results indicate that the SCMF estimated by the modified model is in agreement with those from experiments and finite element method (FEM). Moreover, the effects of electromagnetic and geometrical parameters on the reversal coefficient and Nagaoka coefficient are also investigated. Finally, the model is extended to estimate the SCMF of no-insulation (NI) magnet.

Section: Discussionmentioning

confidence: 99%

A modified model to estimate the screening current-induced magnetic field of a REBCO magnet

Tang¹,

Liu²,

Li³

et al. 2022

“…Hence, zinc cannot be used as a material for overband under high magnetic fields. Although the stainless steel overband can only slightly reduce tensile radial stress, stainless steel is a frequent choice for overband to keep the structural integrity of the coils in high-field magnet experiments due to the great ultimate tensile strength [42,43].…”

Section: The Inhibition Effect and Feasibility Of Overband On The Del...mentioning

confidence: 99%

“…In this regard, the investigation showed that the thermal stress can be reduced by modifying the CTE of the epoxy resin by adding fillers to the epoxy resin [38][39][40][41]. Meanwhile, the overband fabrication technology is also widely used in the epoxy impregnated REBCO pancake coil or no-insulation REBCO coil to reduce the radial and hoop stresses [42][43][44]. Gao et al numerically investigated the effect of overband on the radial stress of the epoxy impregnated REBCO pancake coil during cooling and propose an optimization scheme that divides the coil into several sub-coils based on 2D axisymmetric symmetry models [44,45].…”

Section: Introductionmentioning

confidence: 99%

3D numerical investigation on delamination behavior of the epoxy impregnated REBCO pancake coil

Shen,

Chen,

Peng

et al. 2023

Superconducting coils made of Rare-Earth-Barium-Copper-Oxide (REBCO) coated conductor (CC) exhibit superior electromagnetic performance. Employing epoxy impregnation can improve the structural integrity and mechanical property of the superconducting coils. However, due to the extreme work environment and weak adhesion strength of REBCO CC, the delamination induced by radial thermal stress and electromagnetic force significantly affects the electromagnetic property and the reliability of the superconducting coil. This study proposes a three-dimensional (3D) thermal-electromagnetic mechanical delamination model that incorporates the cohesive zone model (CZM) to investigate the delamination mechanisms in epoxy impregnated REBCO pancake coils during the cooling and coil operation processes. The simulation employs a three-parameter Weibull distribution to account for the inhomogeneity of transverse tensile strength in the CCs. The delamination behavior and mechanisms of the coils under different conditions are analyzed. The simulation results show that the model considering random adhesion strength proves to be more effective in representing the delamination behavior of the coil. And large tensile radial stresses caused by thermal stresses and electromagnetic forces lead to the delamination behavior of the coil during cooling and operation. The main reason for the tensile radial stress is the mismatch in the thermal contraction among components of the coils during cooling process. Furthermore, we investigate the influence of the thermal expansion coefficient (CTE) and thickness of the mandrel, the CTE and prestress of the overband and the initial localized damage. The results indicate that these factors significantly affect the tensile radial stress and the extent of delamination in the windings. And the extent and distribution of delamination is related to the stress release caused by delamination to a certain degree.

“…It is necessary to build an electromagnetic-mechanical coupled model to numerically analyze the influence of the variation of contact resistance induced by mechanical deformation on the electromagnetic behavior of an NI layer-wound coil. Moreover, many reports have verified that overbanding is an effective method to reduce the hoop stress and strain, particularly in NI coils [35,[39][40][41]. A reasonable overband can prevent the deformation and separation between turns of an NI REBCO coil, which motivates us to discuss the influence of overbanding in the high field.…”

Section: Introductionmentioning

confidence: 96%

“…For the NI REBCO coil, the deformation and separation between adjacent turns may have an effect on contact resistance in external fields. Many studis have calculated the mechanical deformations or stresses in REBCO conductors and NI coils numerically [34][35][36][37][38]. However, few works have focused attention on the effect of separation between adjacent turns on the contact resistance of NI coils.…”

Section: Introductionmentioning

confidence: 99%

Numerical analysis of the contact resistance in a no-insulation layer-wound coil with a simplified electromagnetic–mechanical model

Li¹,

Tang²,

Liu³

et al. 2022

Self Cite

The increase in contact resistance of no-insulation (NI) high-temperature superconducting (HTS) coil was observed in the high-field test, which may be related to the mechanical deformation and the separation between adjacent turns in the coil. The large electromagnetic force generated in the high magnetic field can cause the separation between adjacent turns of the NI coil, which can affect the contact resistance of the magnet. An electromagnetic-mechanical model is built to study the effect of separation on the contact resistance and field delay time of an NI layer-wound coil. The numerical results show that the large electromagnetic force generated in the high field leads to the local separation between adjacent turns and the increase of contact resistance of the NI layer-wound coil. Moreover, a higher external field or target current can result in a larger area of separation region, a higher contact resistance and a shorter characteristic field delay time. The overband can restraint the mechanical deformation and separation between turns of the NI coil in the high field, which suppresses the increase of turn-to-turn contact resistance.