A new numerical approach to find current distribution and AC losses in coaxial assembly of twisted HTS tapes in single layer arrangement

Abstract

A new numerical approach to find current distribution and AC losses in coaxial assembly of twisted HTS tapes in single layer arrangement Abstract. This paper presents a novel technique for evaluating AC losses and current distribution in single layer assemblies of coaxially wound thin conductors, such as YBCO coated conductors. The proposed approach takes into account the twisted geometry of the individual superconducting tapes by considering the integral relation between the magnetic vector potential and the current density in the tapes (Biot-Savart formula). The integrals are solved numerically and semi-analytically, and the results are used to generate a discretized system of equations based on the magnetic flux diffusion equation (eddy current problem). The latter is solved using an efficient time transient solver (DASPK). It is assumed that, due to the helical symmetry of the problem, it is sufficient to solve for the current distribution in half of a single tape crosssection, even if many tapes are present, which allows a drastic reduction of the 3-D problem to a simple 1-D domain. The method was used to evaluate the AC losses of a HTS cable made of coated conductors, and it was observed that for a given radius of the former and number of tapes, twisted tapes with smaller pitch have lower AC losses.

A full 3D time-dependent electromagnetic model for Roebel cables

“…Although this model represents a 3D structure, it does not account for the finite thickness of the conductors. Infinitesimally thin approximations have already been used in several instances for 2D and 3D models [8][9][10]. In essence, they do not account for current distributions across the tape's thickness.…”

Assessment of alternative design schemes to reduce the edge losses in HTS power transmission cables made of coated conductors

“…According to the left-hand side of figure 4, as was already known [7,8], with the typical design the AC losses decrease as the size of the gap decreases. In this figure, it is observed that, for a given gap, the AC losses remain the same regardless of the winding angle of the cable.…”

“…As explained, the edge losses arise from the presence of small gaps between the adjacent tapes (shown in figure 2). Therefore, the minimum AC losses with a typical design of single layer HTS cables are achieved when these gaps are completely closed [7,8]. But due to mechanical considerations, there is a minimum size for the gap (0.6-0.8 mm) [8].…”

“…In this paper, for the same number of tapes with the same characteristics used in [10], we investigate the impact of the helical configuration of the tapes on the AC loss behavior with the idea of overlapping the tapes. To consider the helical configuration of the tapes, we use a numerical model developed in our previous work [7,11] to find current distributions and AC losses in helically wound thin tape conductors. In addition to the previously introduced overlapped design (which here is renamed as cyclic overlapped design) we consider two other alternative overlap designs to reduce the edge losses in HTS power cable.…”

Numerical study of AC loss of two-layer HTS power transmission cables composed of coated conductors with a ferromagnetic substrate

“…Moreover, the experimental setup for superconducting cables is very costly and time-consuming. Therefore, using the finite-element method (FEM) in the simulation of AC loss of superconducting power transmission cables, instead of experimental work, has been preferred by many researchers [6][7][8][9][10]. Simulations of cables have also been useful for predicting and understanding the measured loss mechanism for either transport or magnetization loss [11,12].…”