Application of fault current limiter in 22.9 kV KEPCO grid

Abstract

Watertight 25.8 kV/600 A/12.5 kA fault current limiter (FCL) was developed to realize the protection coordination by limiting fault current at 22.9 kV underground distribution systems. In order to maximize an effect of FLC, it is good to install the FCL near to the substation. This FCL is made of watertight structure with rupture disk to prepare for rainy season, and composed of fast fault detector (FFD), mechanical fast switch (FS) and current limiting resistor (CLR). When fault occurs between FCL and downstream protection device in distribution line, the fault is detected by FFD and the fault current is changing its direction from FS to the CLR. If the fault is resolved by downstream protection device such as circuit breaker (CB), the load current flows to the FS again. The limitation of fault current by FCL is perfectly completed within 1 cycle from the moment of fault occurrence. The general technical specification of Korea Electric Power Corporation (KEPCO) for FCL was established, and the performance of FCL was verified by type test and field test. Recently, five FCLs have been successfully installed in KEPCO power grid for the purpose of commercial demonstrations. The distribution lines installed with FCL were analyzed focusing on the protection coordination by over current relays (OCRs) in comparison with before and after application of FCL. And also, we estimate and propose the optimal setting value of the relays.