AC loss in ReBCO pancake coils and stacks of them: modelling and measurement

Abstract

Many applications of ReBCO coated conductors contain stacks of pancake coils. In order to reduce their high AC loss, it is necessary to understand the loss mechanisms. In this article, we measure and simulate the AC loss and the critical current, Ic, in stacks of pancake coils ("pancakes"). We construct stacks of up to 4 pancakes and we measure them by electrical means. We also obtain the anisotropic field dependence of Jc from Ic measurements of the tape. This Jc is the only input to the simulations, together with the coil dimensions. After validating our computations with the measurements, we simulate stacks of many pancakes, up to 32. We found that the AC loss in a stack of (four) pancakes is very high, two orders of magnitude larger than for a single tape. A double pancake behaves as a single one with double width but a stack of more pancakes is very different. Finally, we found that a 2-strand Roebel cable reduces the AC loss in a stack of pancakes but not in a single pancake. In conclusion, our simulations are useful to predict the ac loss of stacks of coated conductor pancake coils and to reduce the ac loss by optimizing the coil design.

Comparison of 2D simulation models to estimate the critical current of a coated superconducting coil

“…7 it can be noted that the magnetic flux densities at the top and bottom coils have same the amplitude, but opposite field angles, when zero angle is defined as the perpendicular field to the tape's wider surface. The fact that the top coil has lower critical current is consistent with the conclusion in [26]. However, in [26] the two critical currents for the top and bottom coils are only slightly different.…”

Development of a three-dimensional finite-element model for high-temperature superconductors based on the H-formulation

“…2-D models have proven to be in excellent agreement with measurement when the 2-D symmetry is also realized in the measurements -see for example [8,10]. In those cases, the magnetic field lines are always perpendicular to the current, and pinning and flux flow in the microscopic scale can be used to describe what happens inside the superconductor [11].…”

A Finite Element Simulation Tool for Predicting Hysteresis Losses in Superconductors Using an H-Oriented Formulation with Cohomology Basis Functions

“…Hence, the nonlinearity of our AC loss modelling problem arises from the nonlinear constitutive equation between E and J in the superconducting subdomains of . Depending on the material, n values between 20 to 50 are quite typical for superconductors under practical operating conditions [1,[25][26][27].…”