Quench transient current and quench propagation limit in pancake wound REBCO coils as a function of contact resistance, critical current, and coil size

Abstract

It is a general belief that no insulation (NI) coil technology is a path to very high field superconducting coils. Recent experience has shown that there are aspects of NI coil design that, if not addressed, can possibly lead to coil failures. One potential problem area is the large transient currents that are associated with quench propagation in NI coils. In an attempt to understand and possibly find ways to minimize the potential for damage from quench transients, a parameter study was undertaken to examine the factors that influence the magnitude of transient currents during quench in NI coils. The characteristics of the transient currents are first examined. A study is then made of a set of test coils, looking at quench propagation and the transient current magnitude as a function of contact resistance, critical current, and importantly coil size. For each coil size, it is found that as the contact resistance increases, the magnitude of quench transient currents is reduced until a condition where effective quench propagation ceases, called the quench propagation limit (QPL). As the QPL is approached, the amplitude of the transient current is decreased and may provide a regime where quench induced stress can be effectively contained in coil designs. As coil size increases, the value of contact resistance associated with the limit of quench propagation increases as well. At large coil sizes that will be characteristic of high field REBCO magnets, the QPL extends to truly large values of contact resistance compared to values observed between bare conductors. The use of methods such as resistive films on conductors and co-wind steel will be required to increase contact resistance. In recognition of this development, the use of high contact resistance achieved in this manner is appropriately called resistive insulation coil technology.

Quench analysis of a no-insulation REBCO magnet based on the ADI method considering the coupling effect of the cryostat

“…During the course of the inductive current quench phase, Imax(t) rises with fluctuation, which stems from the sequential quench propagation within the discrete cells along the radial and axial direction. Similar spike waveforms of the azimuthal current in REBCO coils have also been reported in the previous study [33]. When the quench frontier nearly approaches the end of the coil, Imax(t) reaches a peak value and then dropped quickly.…”

“…Hence it has become a feasible approach for the quench simulation of NI magnets, which is essential for both the preliminary design and failure analysis. To date many works have been done based on this model: Markiewicz et al [32,33] developed an inhouse code based on a 2D PEEC model with a finite difference method thermal model to examine the factors that influence the transient inductive currents of REBCO magnets during quench. Bhattarai et al [34,35] utilized a 2D PEEC model without radial subdivision to understand the quench behaviors of different types of NI REBCO magnets and obtained results relatively consistent with the experiments.…”

Quench and self-protecting behaviour of an intra-layer no-insulation (LNI) REBCO coil at 31.4 T

“…In general, an NI pancake coil has contact resistance R c between turns, which is obtained from contact resistivity ρ ct divided by contact area. Such a parameter strongly affects quench behaviour [26]. For an LNI coil, R c or ρ ct exists at the contact between each turn and the facing copper sheet.…”

Electro-thermal modelling by novel variational methods: racetrack coil in short-circuit

“…Although there has been extensive developments in electro-thermal modeling in magnets [8,[11][12][13][14][15][16][17][18] and fault-current limiters or single tapes [19][20][21][22][23], these usually neglect screening currents. The reason is that taking screening currents into account is highly time consuming and of little relevance for currents well above the critical current.…”