Novel Dual-FCL Connection for Adding Distributed Generation to a Power Distribution Utility

A novel dual-connection of fault current limiters is described for use when connecting new distributed generation plants to the electric grid. The operation and control scheme of this connection are described and analysed. The proximate arrangement of the two current limiters has the advantage that they can share one cryogenic system. The dual connection limits fault currents sufficiently to avoid disturbing the original protection relay schemes of the utilities, and also improves synchronism between the new generator and the grid. These benefits are proven by simulations of a 36 MW, 4.16 kV gas turbine generator connected to an infinite grid. This dual-FCL connection reduces fault current contributions of the DG by 97% (from 41 to 1 kA), and maintains the circuit breakers within their duty limits when a three-phase fault occurs at a bus connected to the DG. Otherwise, when a three-phase fault occurs in the infinite system, this connection limits the fault current contribution of the DG from 4.8 to 0.4 kA, and frequency oscillations of the DG from 0.14 to 0.01 Hz. The power continuity in the local network is improved, as the voltage sag at the bus connected to the DG is reduced by 96% (from 851 to 32 V) during and after serious short-circuit faults.