Electromagnetic-thermal-mechanical behaviors of a no-insulation double-pancake coil induced by a quench in the self field and the high field

Abstract

High-temperature superconducting double-pancake (DP) coils wound by the no-insulation (NI) approach have been proved to have a high thermal stability and a self-protecting ability. This paper mainly studies the effect of a quench of one pancake coil on the electromagnetic-thermal-mechanical behaviors of an NI DP coil in the self field and the high field. An electromagnetic-thermal coupling quench model is used to calculate the distributions of current, temperature and electromagnetic field in the coil, and then a three-dimensional homogeneous mechanical model is built to analyze the changes in strain and stress during a quench by considering the distributions of thermal strain and Lorentz force of the coil. The results indicate that the obvious increase in circumferential current and radial current density in the bottom pancake coil is induced by a quench of the top pancake coil due to the electromagnetic coupling effect in the self field and the high field, and that the DP coil still has a negative coil voltage during a quench in different fields. Although the bottom pancake coil has a large circumferential current, the mechanical deformation of the DP coil during a quench is mainly caused by the temperature rise in the self field. The thermal expansion of the top pancake coil has a remarkable effect on the mechanical behaviors of the bottom pancake coil. Moreover, the DP coil has the same temperature rise and mechanisms of bypass current in the self field and the high field. However, the mechanical deformation of the DP coil is based on the combined effects of temperature rise and Lorentz force in the high field. It can be found that the values of the hoop and axial stresses are affected by a large electromagnetic stress.

Thermomagnetic instability and accompanied stress intensity factor jumps in type-II superconducting bulks under various magnetization processes

“…∆T = T − T 0 . The constitutive relation of stressstrain for the superconducting material can be expressed as [48]…”

Magnetic Field Saturation of Non-Insulation High-Temperature Superconducting Coils during Overcurrent

“…Rj,k represents the k-th radial resistance. Considering that a DP coil is wound spirally with a single tape, the upper pancake is reflectional rather than translationally symmetric [21] with respect to the lower pancake, which should be considered when numbering spiral elements and calculating the mutual inductance between an arc element of the upper pancake and one of the lower pancakes.…”

Performance enhancement of coated conductor magnet with double-layer metal insulation

“…Motivated by the situation described above, two metalinsulation coils with single-layer and double-layer brass tapes were fabricated to compare their contact resistivities through a sudden-discharge test, and to further identify the effectiveness of the double-layer metal-insulation method for increasing the contact resistivity without sacrificing the thermal conductivity. Then, to theoretically understand the influencing mechanism of the contact surface resistivity distributions, a developed thermo-electromagnetic model considering the actual structure of the double-layer insulator was extended to analyze the characteristics of the double-layer metal-insulation coil based on the previous publications [31][32][33]. Finally, we carried out several case studies to observe insights into the performance distinctions of the double-layer metal-insulation coils with different contact surface resistivity distributions under various conditions.…”