Abstract The resistance Superconducting Fault Current Limiter (RSFCL) using YBCO tape is supposed to be of great potential in the high voltage power grids. The fast recovery rate after quenching is the safety guarantee of the electric system to prevent the subsequent fault current shocks. However, the transient heat transfer and local boiling bubble behaviors of liquid nitrogen (LN2) highly affecting the recovery rate are seldom revealed, especially for the disc structure RSFCL with tiny channels. In this work, the boiling heat transfer characteristics during the quenching and recovery process of a YBCO tape in LN2 bath were studied. A 3-D CFD model based on a local part of a typical RSFCL with disc structure was first built to reveal the transient heat transfer coefficient, cooling curve, gas phase volume and temperature distribution that cannot be measured in experiments. The visualization experiment for verification and observation on bubble distribution was conducted with a high-speed camera. Results show that the boiling bubbles generate immediately as quenching starts, film boiling can form quickly within in 0.035 s on the tape surface. The bubble motion behaviour is severely affected by the layout of the Teflon framework. The bubbles detachment from the upper surface of the tape is more frequent than that from the lower surface of the tape, causing inhomogeneous temperature distribution along the tape. Since the recovery is mainly under the film boiling with small heat flux, even a single YBCO tape needs about 2.5 s to return to 77.7 K from 162 K, which means it is impossible to reclose the YBCO tape within 2 s after the quenching cutting off, especially for practical large RSFCL systems with longer recovery time. Besides, there are bubbles still remaining in the system after 5 s when the temperature has recovered to 77.7 K. The remaining gas would change the dielectric field and induce a risk of electric breakdown under the next large impulse current, which should be considered in the safe operation of RSFCL.

中文翻译：

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YBCO带淬火恢复过程液氮沸腾行为模拟与可视化实验

摘要 使用YBCO胶带的电阻超导故障限流器(RSFCL)在高压电网中具有巨大的潜力。熄火后的快速恢复速度是电力系统防止后续故障电流冲击的安全保障。然而，液氮 (LN2) 的瞬态传热和局部沸腾气泡行为对回收率影响很大，很少被揭示，特别是对于具有微小通道的盘状结构 RSFCL。在这项工作中，研究了 YBCO 带在 LN2 浴中淬火和恢复过程中的沸腾传热特性。首先建立了基于具有盘状结构的典型 RSFCL 局部部分的 3-D CFD 模型，以揭示瞬态传热系数、冷却曲线、在实验中无法测量的气相体积和温度分布。气泡分布的验证和观察的可视化实验是用高速相机进行的。结果表明，沸腾气泡在淬火开始时立即产生，薄膜沸腾可以在 0.035 秒内在胶带表面迅速形成。气泡运动行为受到 Teflon 框架布局的严重影响。与胶带下表面相比，胶带上表面的气泡脱落更频繁，导致胶带温度分布不均匀。由于恢复主要是在热通量小的薄膜沸腾下，即使是单个 YBCO 胶带也需要大约 2.5 秒才能从 162 K 恢复到 77.7 K，这意味着不可能在淬火切断后 2 秒内重新闭合 YBCO 胶带，特别是对于具有较长恢复时间的实用大型 RSFCL 系统。此外，当温度恢复到 77.7 K 时，5 s 后系统中仍有气泡残留。残留的气体会改变介电场，在下一个大脉冲电流下引起电击穿的风险，在设计中应考虑到这一点。 RSFCL 的安全运行。