Determining critical activation time of inductive fault current limiters in electric power systems

With the capacity expansion of power systems, fault currents may exceed the interrupting capacity ratings of circuit breakers (CBs). Inductive fault current limiters (FCLs) are able to effectively limit fault currents and maintain circuit breakers on duty. For power systems of different ratings, it is important to decide whether the parameters of an inductive FCL satisfy the requirement of limiting fault currents under a user-defined value. By analyzing the transient performance of fault current limitation processes, the critical activation time of inductive FCLs has been formulated. The critical activation time relates to the system voltage ratings, the inductances of FCLs and the upbound of fault currents choosen by users or CB´s ratings. Fault currents can be limited under any user-defined value when the activation time is shorter than the critical one. The equation reveals that an inductive FCL which works in medium-voltage systems may not be able to limit fault current under a certain value in high-voltage systems. An inductive FCL should be checked according to this equation before it is applied to a paticular power system. These conclusions are verified by simulation results.