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

为了建立可靠、灵活的电力系统，对故障限流器的需求不断增加。特别是高温超导体的发现以来，人们对各种类型的故障限流器进行了研究和开发。磁屏蔽型超导故障限流器（MSFCL）被认为是一种很有前途的实用限流器。为了产生较大的限流阻抗，MSFCL超导磁屏蔽体必须快速加热到临界温度以上。然而，在限流作用的初期，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，它具有解决这一问题的功能。其特点之一是超导磁屏蔽体在发生短路故障后会自动快速升温。故障清除后，也会在短时间内恢复到超导状态。计算机模拟揭示了这些特征。在本项目中，采用所提出的结构对MSFCL进行了热和限流特性的实验研究，以验证这些特性。结果表明，在故障发生后，当施加在限流线圈上的电压设定在与配电线路电压（6.6 kV）对应的适当值上时，超导体在大约1个周期内自动加热到临界温度t_c以上。并对超导回收特性进行了实验研究。结果表明，线路电流为零后，故障限流器在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.