Torque Simulation on NI REBCO Pancake Coils during Quench

Self Cite

The no-insulation (NI) winding technique greatly enhances the thermal stability of REBCO (REBa2Cu3O x , RE = Rare Earth) pancake coils by avoiding burn-out and thermal runaway. The complicated electrical behaviors in NI REBCO pancake coils produce convoluted mechanical behaviors, so that some journal papers reported that high-field NI REBCO pancake coils were mechanically damaged during quench. To apply NI REBCO magnets for practical commercial use, it is important to understand the electromagnetic and mechanical behaviors of NI REBCO pancake coils in detail with both experiments and simulations. To clarify the electrical behaviors, a few simulation methods for NI REBCO pancake coils have been proposed; such as a simple RL parallel equivalent circuit. In these previous models, the radial current paths along the top and bottom of the pancake coils are represented as one current circuit path. However, since the radial current path of the bottom of one pancake coil is actually very close to that of the top of the next lowest coil, inductive behavior between these two paths appears. The simulation results show a probability that different amounts of radial current on the top and bottom of one pancake coil are carried during quench.

“…This force appeared as a torque in REBCO coils. The possibility of damaging terminals or coils themselves during quench was shown in the previous paper [19].…”

Section: Introductionmentioning

confidence: 87%

“…In our previous research using a partial element equivalent circuit model (PEEC), a torque simulation on NI REBCO double pancake coil have been conducted [19]. When a normal state transition occurred in an NI REBCO pancake coil, the operating current changed from the circumferential to the radial direction through the contact of turns.…”

Section: Introductionmentioning

confidence: 99%

Unbalanced radial current flow simulation of no-insulation REBCO pancake coils during normal state transition

Kurauchi¹,

Noguchi²

2020

Self Cite

“…Driven by curiosity regarding the distinctive attributes of NI REBCO coils such as the self-protecting nature and its intrinsic mechanism, the distributed network model has been widely used to study the electromagnetic-thermal-mechanical behaviors of NI REBCO pancake coils in various normal and off-normal operation conditions, such as charging and discharging tests [17,19,20], overcurrent tests [21,22], post-quench process analysis [19,23], mechanical behaviors during quench [24,25] and screening current effect [26]. Among these studies, a massive system of circuit equations stemming from a distributed network model needs to be solved usually along with a thermal model or mechanical model at each time step, which leads to rather a time-consuming simulation process and high computational efforts.…”

Section: Introductionmentioning

confidence: 99%

Quench analysis of a no-insulation REBCO magnet based on the ADI method considering the coupling effect of the cryostat

Zheng,

Liu,

Song

et al. 2023

A no-insulation (NI) REBCO superconducting magnet is under development at Wuhan National High Magnetic Field Center, China. The magnet with the liquid helium cryostat system has a compact structure to reduce the space required for operation. During a quench, the fast-changing spatial magnetic field around the NI magnet may induce a strong eddy current in the conductive parts of the cryostat. The eddy current and its associated Lorentz force will generate mechanical stress on the cryostat, especially on the thermal shield (TS). The mechanical strength of the cryostat needs verification in the preliminary design. Furthermore, the degree to which the electromagnetic coupling between the cryostat and NI magnet might impact the quench behaviors of the NI magnet remains uncertain. In this paper, a multi-physics quench model is newly developed for the NI REBCO magnet, and the alternating direction implicit method is employed for the solver of the thermal model to improve computational efficiency. This simulation model can consider the electromagnetic coupling effect between the NI magnet and cryostat by constructing a partial element equivalent circuit. A quench analysis has been performed and we found that: (1) The cryostat can function as a secondary shorted circuit to the NI magnet and slow down the quench speed to a certain extent. (2) During the rather fast inductive quench phase, the cryostat will experience an attraction force towards the quench propagation frontier. (3) A quench propagation from one end of the magnet can cause a significant z-axis unbalanced force on the TS. (4) Cryostat materials with drastically changed electrical conductivity can significantly affect their mechanical responses during a quench. However, the eddy current density and maximum Von Mises stress on the TS are barely affected by the thickness of the TS and the contact resistance of the NI REBCO magnet.

“…However, a full resolution model of such NI coils is practically difficult to implement due to the high aspect ratio of the superconductor and the need to consider the currents flowing normal to the conductor's surface. While progress has been made using circuit grid models (CGM) [18,[24][25][26][27], these models lose axial fidelity and cannot simulate the associated shielding currents, and associated stress [28], within the HTS windings [23,[29][30][31].…”

Section: Introductionmentioning

confidence: 99%

Finite-element modelling of no-insulation HTS coils using rotated anisotropic resistivity

Mataira¹,

Ainslie²,

Badcock³

et al. 2020

The no-insulation (NI) winding method is an effective technique for winding coils from high-T c superconductors (HTS). NI coils are electrically and thermally robust due to their ability to radially bypass current away from the fragile superconducting path when necessary. This avoids stored magnetic energy being entirely discharged on local defects in the HTS tape. However, the increased degrees of freedom for the current distribution makes finite-element modelling of these coils a complicated and multi-level problem. Here we present and validate a 2D axially symmetric model of an NI (or partially insulated) coil that captures all the inherent electromagnetic properties of these coils, including axial vs radial current flow and critical current suppression, and also reproduces the well-known charging and discharging characteristics. The model is validated against previously reported discharge measurements, and is shown to produce results consistent with the expected equivalent-circuit behaviour. Only by solving the NI coil problem with both axial and radial fidelity can the interplay of critical current anisotropy and turn-to-turn current be properly accounted for. The reported FE model will now enable coil designers to simulate key complex behaviours observed in NI coils, such as shielding currents, magnetic field inhomogeneity and remnant field effects.