电阻型超导限流器失超过程激增气泡对液氮绝缘击穿特性影响规律研究

Resistive type superconducting fault current limiters (R-SFCLs) with advantages of fast response speed and deep current limit ability are the frontiers and hotspots of research in the field of current limiters. During the quench of the R-SFCLs, quench generating bubbles seriously affect the insulation properties of liquid nitrogen. Current research of the effect of the bubbles on the liquid nitrogen breakdown characteristics is mostly studied through injecting or heating generating bubbles, which is different from the case when the bubbles rapidly growing and drastically changing during quench of superconducting tapes. And there is a lack of research on the effect of bubble accumulation on liquid nitrogen breakdown characteristics in the process of quench-recovery-re-quench of superconducting tape under the requirement of automatic reclosing. The project is based on the actual working conditions of the R-SFCLs. Quench generating bubbles are produced by applying short circuit current to the superconducting tapes to quench the tapes. The amount, velocity, accumulation form and the distribution of the quench generating bubbles during the quenching process of the R-SFCLs are studied. The accumulation effect and interaction of bubbles during the quench-recovery-re-quench process of superconducting tape are analyzed. The effect of bubble generation-decrease-regeneration process on the breakdown characteristics of liquid nitrogen insulation is obtained. The superconducting quenching resistance model and the superconducting electromagnetic thermal coupling model are established. The electric field distribution and breakdown field strength of the R-SFCLs are simulated. The mechanism of liquid nitrogen insulation breakdown is revealed and the internal insulation design criteria of the R-SFCLs are proposed. These studies provide theoretical basis and technical support for the insulation design of superconducting fault current limiter.

具有反应速度快、限流程度深优势的电阻型超导限流器是当前限流器领域研究的前沿和热点。电阻型超导限流器失超过程中产生气泡严重影响液氮的绝缘特性。现有的关于气泡对液氮击穿特性影响的研究多通过注入或加热产生气泡的方式，与超导带材失超气泡快速增长、激烈变化的情况不同，更缺乏自动重合闸要求下超导带材失超-恢复-再失超过程中积累气泡对液氮击穿特性影响的研究。项目基于电阻型超导限流器的实际工况，施加短路电流使超导带材失超产生激增气泡，研究限流器失超过程中激增气泡的数量、运动速度、积聚形式和分布规律；研究超导带材失超-恢复-再失超过程中气泡的积累效应和相互作用，获得气泡产生-消减-再产生过程对液氮绝缘击穿特性的影响规律；建立超导失超电阻模型和超导电磁热耦合模型，仿真分析限流器内部电场分布和击穿场强，揭示液氮绝缘击穿机理，提出电阻型超导限流器内部绝缘设计准则，为超导限流器的绝缘设计提供理论依据和技术支撑。

电阻型超导限流器利用超导独特的零电阻和超导态-正常态转变特性限制故障电流，是一种理想的限流设备。电阻型超导限流器失超过程中激增气泡对液氮绝缘击穿特性的影响是研制高电压等级超导限流器需要考虑的关键问题。据此，本项目首先研制了10kV/10kA大容量超导限流自激振荡直流开断样机，得到超导限流直流断路器开断过程中超导带材失超特性曲线及热通量值；然后，实验研究了影响液氮/气泡复合系统击穿电压的关键因素，得到气泡导致的电场畸变是使液氮绝缘水平降低的关键因素；之后，针对电阻型超导限流器的重合闸运行工况，研究了超导带材“失超-恢复-再失超”过程中气泡的形态、数量，超导带材的失超电压、产热和恢复状态，建立了超导电磁热多物理场耦合模型，获得了重合闸时间、电极间距、通流电流等因素对液氮/气泡复合系统击穿电压、超导温度变化和恢复时间的影响规律，得到设计超导限流器内部绝缘强度时需考虑二次失超时累积气泡对液氮绝缘强度的影响。此外，项目额外提出通过施加绝缘屏障提高电阻型超导限流器内部液氮复合系统绝缘强度的方法，得到通过合理设计屏障可使正、负极性绝缘屏障/液氮/气泡复合绝缘系统的直流击穿电压与无屏障时相比分别提升1.24倍及1.30倍；而且，项目研究了绝缘屏障/液氮/气泡复合绝缘系统的沿面闪络特性，得到随着绝缘屏障向双针电极侧靠近，击穿路径由绝缘屏障体击穿转换为绝缘屏障沿面闪络，激增气泡使复合绝缘系统由绝缘屏障体击穿放电模式转换为沿面闪络放电模式的概率增加。最后，建立了考虑超导“失超-恢复-再失超”工况的液氮/气泡复合系统击穿电压预测模型、绝缘屏障/液氮/气泡复合绝缘系统击穿电压及沿面闪络电压预测模型，提出了电阻型超导限流器和绝缘屏障式超导限流器内部绝缘优化设计策略。项目研究结果对设计电阻型超导限流器内部绝缘，提高绝缘可靠性，促进设备小型化，推动高电压等级超导电力设备和低温高电压绝缘技术的发展具有重要的理论和实际意义。