Analytical and empirical studies on the characteristic resistances of no-insulation GdBCO racetrack pancake coil under various operating currents

Kim, K.L.; Choi, Yoon Hyuck; Yang, Dong; Kang, Dahyun; Kim, J.H.; Kim, H.M.; Lee, H.G.

doi:10.1016/j.cap.2014.10.029

Cited by 23 publications

(3 citation statements)

References 27 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Insulated coils -in which the coil is either co-wound with an electrical insulator or the conductor itself has an insulator coating -suffer from stability issues and are prone to damage due to local defects. Non-insulated (NI) coils [4], where the HTS tapes are wound without turn-to-turn insulation, are also actively researched [5][6][7][8][9][10][11] as an alternative. One of the main benefits of such coils is their proven selfprotecting behavior [4,12,13] due alternative current paths via the turn-to-turn resistances.…”

mentioning

confidence: 99%

Fluorescent thermal imaging of a non-insulated pancake coil wound from high temperature superconductor tape

Gyuráki

Benkel

Schreiner

et al. 2019

Supercond. Sci. Technol.

View full text Add to dashboard Cite

We have wound a 157-turn, non-insulated pancake coil with an outer diameter of 85 mm and we cooled it down to 77 K with a combination of conduction and gas cooling. Using high-speed fluorescent thermal imaging in combination with electrical measurements we have investigated the coil under load, including various ramping tests and over-current experiments. We have found found that the coil does not heat up measurably when being ramped to below its critical current. Two over-current experiments are presented, where in one case the coil recovered by itself and in another case a thermal runaway occurred. We have recorded heating in the bulk of the windings due to local defects, however the coil remained cryostable even during some over-critical conditions and heated only to about 82-85 K at certain positions. A thermal runaway was observed at the center, where the highest magnetic field and a resistive joint create a natural defect. The maximum temperature, ∼100 K, was reached only in the few innermost windings around the coil former.

show abstract

mentioning

confidence: 99%

Fluorescent thermal imaging of a non-insulated pancake coil wound from high temperature superconductor tape

Gyuráki

Benkel

Schreiner

et al. 2019

Supercond. Sci. Technol.

View full text Add to dashboard Cite

show abstract

“…As aforementioned [15][16][17], the contact resistivity changes with surface roughness and tolerance, load cycles, thermal cycles, stress, and temperature etc. Moreover, Kim et al [28] observed that the turn-toturn contact within the coil was enhanced with larger amplitude of current due to the increased Lorentz force when a NI coil was ramped up with the same ramping rates. It is quite difficult to maintain a constant contact resistivity after winding the NI coil because of these multiple impacting factors.…”

Section: Analysis Of Sudden-discharge and Charge Processmentioning

confidence: 99%

Study of contact resistivity of a no-insulation superconducting coil

Liu

Gyuráki

et al. 2021

Supercond. Sci. Technol.

View full text Add to dashboard Cite

Previous studies of test coils have demonstrated the high thermal and electrical stability of no-insulation (NI) high temperature superconducting (HTS) coils thanks to the presence of turn-to-turn current paths. These turn-to-turn current paths in a NI coil are significantly influenced by the contact resistivity. In practice, it is very challenging to measure the contact resistivity of a NI coil by direct experiments of short samples, since the contact resistivity of superconducting tapes is influenced by surface roughness and tolerance, stress, temperature etc. A proper simulation model is needed to investigate the contact resistivity of the NI coils with dedicated experiments. Hence, in this paper a distributed circuit model is employed. This model, implemented in Matlab 2018a, considers the local contact resistivity, self and mutual inductance, and HTS resistance, which depends on the supplied current, magnetic field and temperature. To validate the model, experimental results from literature, including sudden discharge, and charge–discharge processes, are employed and the results from simulations are consistent with experimental results. Then the model is used to investigate the equivalent contact resistivity of a 157-turn NI coil. Through the comparison of simulated and experimental results, it is found that the contact resistivity of the NI coil has an inhomogeneous distribution. When the current changes with different speeds, ramping rates or frequency, a different number of turn-to-turn contacts carries radial current. Since the turn-to-turn contacts have different contact resistivity, the equivalent contact resistivity calculated from sudden discharge cannot be used in simulations to reproduce all the experimental data.

show abstract

“…However, R C for the straight section in a racetrack coil depends on the Lorentz force induced by the excitation current. Because the Lorentz force dissipates as the coil current is instantly decreased to zero, R C is not at all affected by the Lorentz force during a sudden charge [32,42]. Therefore, it is more appropriate to calculate the R C of the NI HTS racetrack coil using the charge time constant.…”

mentioning

confidence: 99%

A Flux-Controllable NI HTS Flux-Switching Machine for Electric Vehicle Applications

2020

View full text Add to dashboard Cite

This paper deals with a flux-controllable NI HTS flux-switching machine (FSM) for electric vehicle (EV) applications. In a variable-speed rotating machine for EVs, such as electric buses, electric aircraft and electric ships, an electric motor capable of regulating the flux offers the advantage of constant output operation. In general, conventional HTS rotating machines have excellent flux-regulation performance, because they excite an HTS field coil. However, it is difficult to ensure any flux-regulation capabilities in HTS rotating machines using HTS field coils that apply the no-insulation (NI) winding technique, due to the inherent charge and discharge delays in these machines. Nevertheless, the NI winding technique is being actively researched as a key technology for the successful development of HTS rotating machines, because it can dramatically improve the operational stability of HTS field coils. Therefore, research to implement an HTS rotating machine with flux-regulation capabilities, while improving the operating stability of the HTS field coil using the NI winding technique, is required for EV applications. In this paper, we propose an HTS rotating machine with a flux switching structure, a type of topology of a rotating machine that is being actively studied for application to the electric motors used in EVs. The proposed HTS flux-switching machine (FSM) uses NI field coils, but additional field windings are applied for flux regulation, which enables flux control. In this study, an NI HTS field coil was also fabricated and tested because the characteristic resistance value should be used for the design and characteristic analyses of machines which utilize an NI coil. The simulation model used to analyze the flux-regulation performance capabilities of the NI HTS FSM were devised based on the characteristic resistance values obtained from a charging test of the fabricated NI HTS field coil. This study can provide a good reference for further research, including work on the manufacturing of a prototype NI HTS FSM for EV applications, and it can be used as a reference for the development of other HTS rotating machines, such as those used in large-scale wind power generation, where flux-regulation capabilities are required.

show abstract

Analytical and empirical studies on the characteristic resistances of no-insulation GdBCO racetrack pancake coil under various operating currents

Cited by 23 publications

References 27 publications

Fluorescent thermal imaging of a non-insulated pancake coil wound from high temperature superconductor tape

Fluorescent thermal imaging of a non-insulated pancake coil wound from high temperature superconductor tape

Study of contact resistivity of a no-insulation superconducting coil

A Flux-Controllable NI HTS Flux-Switching Machine for Electric Vehicle Applications

Contact Info

Product

Resources

About