Magnetization loss of no-insulation coil for an electrodynamic suspension system

Abstract

A high-temperature superconducting no-insulation (NI) coil, with its self-protection property, high engineering current density and unique demagnetization property, becomes a potential candidate for an electrodynamic suspension (EDS) system. Compared with the applications in high field magnets, the NI coil used in the EDS system is considered as working in a dynamic state, the magnetization loss generated in the NI coil is essential for the design of a cryogenic system. This paper presents the study on AC magnetization loss of NI coils by both numerical and experimental methods. Firstly, a 3D finite element numerical model representing the full geometry of the NI coil is built to analyse the effect of field frequency, field magnitude, as well as the radial characteristic resistance. Then, systematic discussions are conducted to figure out the working mechanism of NI coils. Finally, a calibration-free method testing platform is installed to validate the numerical model, and a modified model is proposed to represent the non-uniform radial characteristic resistance caused by stress distribution. The conclusions of this paper will be used in the future optimization of NI coils and the cryogenic design of the EDS system.

Time-variant magnetic field, voltage, and loss of no-insulation (NI) HTS magnet induced by dynamic resistance generation from external AC fields

“…In previous experiments, Lu et al have derived the non-uniform ρ t2t distribution that the innermost and outermost turns have the largest ρ t2t values through refined voltage measurements for different sections of their NI coil [61]. Wang et al have found that experimental results agree better with the simulation results setting larger ρ t2t value for the outermost turns [62]. Liu et al observed that the NI coil sample with ρ t2t = 90 µΩ•cm 2 indicated from a sudden discharge test, if operated with a highfrequency AC transport current supply, behaves like an NI coil with ρ t2t = 500 µΩ•cm 2 , which is also explained to be the local non-uniform ρ t2t distribution [39].…”

Study of the demagnetization behavior of no-insulation persistent-current mode HTS coils under external AC fields by 3D FEM simulation

“…Qin et al [50] and Noguchi and Hahn [51] proposed the refined circuit and advanced partial element equivalent circuit models, which are based on the conventional circuit grid models with the tape elements divided in the width directions. For finite-element method (FEM) models, Zhao et al [52] and Wang et al [53] proposed 3D models that built all the distinct HTS tapes including the specific turn-to-turn-contact and superconducting layers. Schnaubelt et al [54] built an NI HTS coil model based on the H−ϕ formulation with the turn-to-turn contact layers modeled as the shell elements.…”

A non-destructive method for detecting turn-to-turn resistivity distribution in NI REBCO coils

“…A portion of the current in the NI coils will be forced to flow into the inter-turn paths during unsteady conditions such as excitation, demagnetization and quench, resulting in delayed charging and discharging [13], complicated quality degradation in the magnetic field [14,15] and stress concentration problem [16,17]. Additionally, the alternating background magnetic field also induces radial currents in the NI coils or similar cables, which leads to inter-turn losses [18,19], distinct dynamic resistance distribution from the insulated coils [20][21][22], and the redistribution of coil currents and spatial magnetic fields [23]. In closed-loop NI coils during the excitation process, non-uniform distribution of circumferential and radial currents and their continuous redistribution processes will be experienced after turning the persistent current switch to be superconducting and lead to a misunderstanding of the field decay rate [24].…”

“…To accurately predict the behaviour of NI coils during unsteady conditions, it is crucial to set up a 'good' distribution of TTRD in the simulation model. In recent years, an increasing number of studies have reported that setting only a uniform TTRD in simulation models is not sufficient to accurately predict the behaviour of NI coils in experiments [18,[24][25][26]. In fact, the TTRD of NI coils is affected by various factors including surface condition [27], temperature [12], number of thermal cycles [2] and turn-to-turn contact pressure [1] which is influenced by winding tension [28], thermal stress [28] and electromagnetic force [29].…”