Theoretical estimation of quench occurrence and propagation based on generalized thermoelasticity for LTS/HTS tapes triggered by a spot heater

No-insulation (NI) high-temperature superconducting (HTS) coils exhibit high thermal stability and self-protecting features compared with traditional insulated HTS coils. As NI coils experience heat disturbance, the underlying mechanism of the heat propagation, the changes of the central field and voltage of the coil need to be further explored. Moreover, due to the rapid temperature rise caused by the heat disturbance, the coil typically suffers from large strain and stress. Therefore, the mechanical behavior is also a vital factor in the design and operation of superconducting magnets. This paper proposes a multiphysics quench model to study the thermal stability, composed of an equivalent circuit axisymmetric model combined with a two-dimensional magnetic field model and a one-dimensional (1D) heat transfer model. An additional 1D solid mechanical model is used to analyze the mechanical behavior of the NI coil. The results indicate that when the temperature of the coil exceeds its critical value, the current flows along the radial direction. The heat generated by the radial resistance of the coil is small, so that it is difficult to induce a quench. The thermal expansion and heat propagation velocity also affect the distributions of the hoop and radial stresses in the coil. The change of the hoop stress is larger than that of the radial stress, and the electromagnetic force has a relatively small effect in the self-field. The pulsed energy, inner diameter of the coil and location of the heater are all found to have an observable effect on the thermal stability and mechanical behavior.

“…The strain has proved to be an effective method to detect the quench [31,32]. Moreover, the mechanical behavior has an impact on the turn-to-turn contact resistivity [25,30].…”

Section: Solid Mechanical Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Thermal stability and mechanical behavior in no-insulation high-temperature superconducting pancake coils

Liu

Zhang

Yong

et al. 2018

“…Our recent investigations revealed that, as quenching proceeds in a superconducting magnet, sharp variations occur in the strain, strain rate, temperature, and magnetic fields [33][34][35][36]. Therefore, a strain-based quench-detection method for detecting a quench event in LTS magnets using cryogenic strain gauges combined with Wheatstone half-bridge compensation circuits has been proposed [33,34].…”

Section: Introductionmentioning

confidence: 99%

Quench detection and early warning based on thermoelastic strain rate for HTS tapes thermally triggered by heat spots

Chen¹,

Guan²,

Tong³

et al. 2022

Self Cite

The rapid detection and comprehensive monitoring of quench onset and evolution in high-temperature superconducting (HTS) materials remain immensely challenging because the normal zone propagation velocity in HTS materials is two or three orders of magnitude less than that in low-temperature superconductors. In this study, we experimentally and numerically explore quench events triggered by heat spots in yttrium barium copper oxide HTS tapes to characterize the quench onset and propagation. A multiplexed fiber Bragg grating sensor with multiple gratings was used to perform highly accurate strain measurements. Conventional voltage and temperature measurements were performed synchronously on the HTS tapes. A systematic comparison of these multifield signals during quench onset and development illustrated that the evolution of thermoelastic strain and strain-rate in HTS tapes captures the quench onset and propagation. A distinct feature was exhibited during the quenching of a pre-tensioned HTS tape: the thermoelastic strain initially relaxed but subsequently increased until the strain rate exhibited a significant slope change, which corresponded to the quench onset time. The thermoelastic strain in a nearly unconstrained HTS tape gradually increased until quenching occurred. A prominent characteristic for detecting quench onset in HTS materials have been revealed based on the change in the slope of the thermoelastic strain-rate or the second derivative of the strain remaining nearly constant. For a pre-tensioned HTS tape, the minimization of the thermoelastic strain or the strain-rate becoming zero may be a predictor that preceded the quench by 1–2 s, which can be, to a certain extent, regarded as an early warning. Another important and novel result was the experimental demonstration of global strain responses distant from the quench location in the pre-tensioned HTS tape, while the temperature and voltage detection are commonly localized methods. The mechanism behind these thermoelastic strain characteristics was further discussed and simulated from the induced Joule heating throughout the quench event. The measurements and numerical predictions suggested a new paradigm of quench detection based on the thermoelastic strain-rate in HTS materials.

“…The magnet excitation and quench tests were performed on superconducting solenoid magnets [49,50], and the transient strains and their abrupt changes were compared with the current, magnetic field, and temperature signals collected during excitation and quench tests to indicate that the SG measurements could detect the quench of the superconducting magnet. Furthermore, the mechanism for the abrupt change of strain and strain rate in a superconducting magnet during a quench was explained using a dynamic thermoelastic model with a relaxation time based on generalized thermoelastic theory [51]. Additionally, strain measurement during quench was also validated as an effective quench-detection method for both LTS and HTS magnets [52][53][54].…”

Section: Introductionmentioning

confidence: 99%

A dynamic strain-based quench-detection method in an LTS sextupole magnet during excitation and quench

Gao

Guan

Xin

2020

Self Cite

The dynamic strain characteristics and responses of a low-temperature superconducting (LTS) magnet during excitation and a quench are investigated in the present work. For the strain measurements, strain gauges in the form of a half-bridge circuit comprising cryogenic strain gauges and their dummy resistances are embedded directly within the superconducting magnet structure. A wireless high-speed data acquisition system with a resolution of 1 ms is also used to obtain the strain history of the LTS magnet during operation. The dynamic strain induced by thermal or mechanical disturbances is detected promptly and compared with the transport current and temperature signals recorded during a quench. This indicates that the dynamic strain measured in the LTS magnet can capture a quench feature in a timely manner. For a better understanding of the dynamic strain histories in the magnet, the dynamic strain signals are subjected to spectral analysis during the excitation and pre- and post-quench processes. It is shown originally that several spectral peaks on strain measured are always observed at the onset of a quench. Thus, the dynamic strain characteristics and responses provide a evaluation means of superconducting magnet.