Design parameters influencing non-uniform current distributions in superconducting multi-stage stranded cables

Multi-strand superconducting cables, e.g., cable in conduit conductors (CICCs), are applied to large-scale apparatus, such as fusion machines. In this sort of cable, strands carry different currents. This phenomenon is known as nonuniform current distribution (NUCD). NUCD causes increase of AC loss and/or instability of the cable. During the energization, induced voltage occurs along each strand and the minute difference between induced voltages results in the circulation current through the closed circuit composed of two different strands. Superposing these circulation currents and transport one, NUCD appears. The leakage inductance along the pair of strands is around 10 7 H m, thus the minute difference between induced voltages can produce large circulation currents. In spite of this fact, conventional NUCD simulations are fulfilled with ideal circuit models. Here, the ideal model consists of superposition of sinusoidally waving tracks of the strands. We made a numerical electric circuit model based on real tracks of strands simulating actual multi-strand cable. We considered mechanical interactions between the strands and proposed the solution about the strands' positions based on the mechanical energy minimum principle. Establishing suitable circuit model, we successfully calculated NUCD. Finally, NUCD due to the deformation of the cable's cross section was discussed. The deformation is caused by the electromagnetic force or cross sectional forming into rectangular shape.Index Terms-Induced voltage, multi-strand superconducting cable, nonuniform current distribution.

Section: A Tracks Of Strands and Deformation Of The Cablementioning

confidence: 76%

Numerical Analyses of Non-Uniform Current Distribution Within the Multi-Strand Superconducting Cable for Fusion Apparatus

Seo

Takahata

Mito

et al. 2004

“…8(a-4), framed sub-cables don't go through this region. This is because the strands are not transposed perfectly [13]. In contrast, the stress distributions through the strands are even in our sample due to the external force.…”

Section: B Comparison Of Trapse and Actual Conductor Samplesmentioning

confidence: 84%

Mitigation of Critical Current Degradation in Mechanically Loaded ${\hbox{Nb}}_{3}{\hbox{Sn}}$ Superconducting Multi-Strand Cable

Seo

Nishimura

Hishinuma

et al. 2008

It was reported that Lorentz force caused degradation of critical current in the ITER-TFMC conductor. We have used our novel experimental setup, which utilizes the closed electric circuit concept for critical current and stability measurements of multi-stand superconducting cables. The feature of this setup is mechanical loading applied to the multi-strand cable in the transverse direction. Significant degradation in the critical current of the cable was observed when the average compressive stress was about 20 MPa. This degradation was found irreversible after unloading. We tested the cable with epoxy or ice molds as well. No degradation was observed in the molded cables. We also tested the cable with smaller void fraction. In this case, significant degradation in critical current was observed.

“…However, CICC has a problem of imbalanced current among each strand which produces ramp rate limitation (RRL) [1], [2]. The imbalance of current is caused by a disorder of cabling and difference of inductance of each wire despite of removal of surface insulation [3], [4]. It also avoids conductor to flow the current up to rated current if ramp rate is very high.…”

Section: Introductionmentioning

confidence: 99%

Current redistribution under imbalanced condition in cable-in-conduit conductors

Mori

Takahata

Nishimura

2002

Cable-in-conduit conductors possess possibility of nonuniform current distribution among strands. Any strand reaching to the critical current may lead the whole conductor to the quench. However, current redistribution will play a major role in avoiding such a quench. In this paper, the enhancement of normal-zone propagating current of a superconducting cable due to the current redistribution was studied experimentally. In the experiment, the current redistribution was confirmed, and the normal-zone propagating current, of the cable became higher than the critical current of the strand.has been investigated under several coolant conditions. As a result, in liquid helium had the highest value compared with in sub-cooled or supercritical helium. This difference clearly appeared by the usage of latent heat when the temperature of the strand rose.Index Terms-Cable-in-conduit conductor, current redistribution, normal-zone propagating current ( ), supercritical helium.