Research on Advanced Superconducting Fault Current Limiter with Both Quick Current Limiting Function and Superconducting Recovery Characteristics

为了建立一个可靠和灵活的电力系统，对故障电流限制器的需求越来越大。自高温超导体被发现以来，人们对各种类型的故障限流器进行了大量的研究和开发。磁屏蔽型超导限流器(简称MSFCL)被认为是实用型超导限流器的候选方案之一。MSFCL的超导磁屏蔽体必须在临界温度以上快速升温，才能产生大的限流阻抗。然而，在限流动作的早期阶段很难将其加热到如此高的温度，作者提出了一种高性能的MSFCL，它将具有解决这一问题的功能。其中一个特点是，超导磁屏蔽体在发生短路故障后会自动快速升温。当故障被清除后，它还将在短时间内恢复到超导状态。这些特征是通过计算机模拟揭示的。在本项目中，对采用该结构的MSFCL进行了热限流特性和电流限流特性的实验研究，以验证该特性。结果表明，当加在限流线圈上的电压超过配电网电压(6.6kV)时，超导体在故障发生后约1个周期内自动升温到临界温度T_c以上。对超导恢复特性也进行了实验研究。结果表明，线路电流过零后，故障限流器可在1 S内迅速恢复到超导状态。给出了超导快速恢复冷却结构的设计准则。

The needs for fault current limiters are increased in order to establish a reliable and flexible power system. The research and development on various types of fault current limiters have been conducted especially since the discovery of the high temperature superconductor. A magnetic shield type superconducting fault current limiter (denoted as MSFCL) is thought to be one of the promising candidates for the practical one. The superconducting magnetic shielding body for MSFCL has to be heated up quickly over the critical temerature in order to produce large current limiting impedance. It is, however, difficult to heat it up to such a high temperature in the early stage of current limiting action.The authors proposed a high-performance MSFCL which would have functions to solve such a problem. One of the features is that the superconducting magnetic shielding body will be heated up automatically and quickly after a short circuit failure occurs. It will also be recovered to superconducting state in a short period of time when the fault is cleared. Those characteristics were revealed by computer simulations. The researches on the thermal and current limiting characteristics were conducted experimentally for the MSFCL with the proposed structure to verify such characteristics in this project. It was revealed that the superconductor was automatically heated up over the critical temperature T__c within around 1 cycle after a fault occurs when the voltage applied to the current limiting coil is set over an appropriate value which corresponds to the distribution power line voltage (6.6 kV). The superconducting recovery characteristics were also studied experimentally. It was shown that the fault current limiter will be recovered quickly into a superconducting state within 1 s after the line current becomes zero. The design criterion of cooling structure for fast superconducting recovery was also shown.