A Can Improve Power Quality, Fault Current Limiter

The growth of electric power consumption has resulted in a corres-ponding development of power system, in addition the requirement for the stability of the large system has increased. Utilities are faced with fault current which can exceed the rated capacity of the installed circuit breakers and other equipments, and the fault often result in a serious voltage sag which can make the power quality lower. To correct these problems, a fault current limiter(FCL)is available.This paper has analyzed the advantages and disadvantages of various fault current limiters with reference to the research achievements of short-circuit current limiters that have been reported, a Fault current limiter that according to transformer-type reactor is proposed. This FCL is composed of a capacitor in parallel with primary side of the reactor, and its second side is connected to a discharge gap. It can realize trace, detection and performing function automatically, according to the variation of the voltage drop across capacitor. In normal operation conditions, the voltage across capacitor is very small and discharge gap does not breakdown, so the inductive reactance of the reactor is two orders of magnitude higher than the capacitive reactance of the capacitor and series with a inductance, the FCL can attain to the goal of controllable series compensation. When there is a large fault current in power systems, discharge gap breakdown, the inductive reactance of the reactor decreases and becomes comparable with the capacitive reactance of the capacitor, the circuit produces a large impendence that reduces the fault current due to occurrence of parallel resonance.the author has analyzed its working principle and characteristic in detail. Then, mathematical model and circuit configuration of the FCL are introduced, and system simulation is made by applying electromagnetic transient program(EMTDC) software, the result proves the feasibility of the FCL. In addition, this paper also analyze the characteristic of this FCL affecting to voltage sags due to short fault in three model systems of different net structure.The better performance of the FCL is proved by simulation. It will be a practical protective device for restraining the short-circuit current in power systems in the future.