Fault Current Limiting Using Continuously Variable Series Reactor

This paper discusses a novel method for fault current limiting using a Continuously Variable Series Reactor (CVSR). CVSR is a device that can vary the reactance in an ac circuit using the magnetizing characteristic of its ferromagnetic core shared by an ac and dc windings. A dc bias current in the CVSR's ac equivalent reactance to control power flows, balance loads, and limit fault currents. A proper use of this device requires comprehensive understanding of its characteristics. For this purpose, the Gyrator-Capacitor approach has been applied to model the relatively complex electromagnetic circuit with an equivalent electric circuit. A detailed analysis of the CVSR in terms of currents, induced voltages, and magnetic fluxes is presented. A unique CVSR configuration is considered based on which the novel method of fault current limiting is proposed. A pair of ac coils wound on the same leg and connected in anti-series connection during normal conditions, create magnetic fluxes that cancel each other and result with a low impedance. During fault condition, the CVSR is automatically reconfigured to present high impedance in the circuit and limit the fault current to a desired level. Simulation results demonstrate the feasibility and effectiveness of the proposed method.