An Equivalent Magnetic Circuit Coupled Model of PMFCL for Transient Simulation

Fault current limiters are required to restrict the excessively large short-circuit currents. With several incomparable merits such as compactness, small size, reliable operation and zero reset time, the permanent-magnet-biased saturated iron core fault current limiter (PMFCL) falls into many researchers concern for its prospective commercial application in power systems. The PMFCL is a combination of one permanent magnet, two lamb cores and two coils. The permanent magnet is used to bias the two cores into saturation under normal condition. The coils are wounded around the two core lambs and connected in series with the electrical circuit. Under normal operating condition, the cores are in saturation state and the PMFCL behaves like an air-core reactor with low impedance. During large fault currents, the cores come out of saturation on alternate half-cycles of the supply current and the impedance of the PMFCL rises to a large value to limit the fault currents. In this paper, a series of magnetic circuit formulas have been presented. The equivalent magnetic analysis is used to simulate the PMFCL's transient process with MATLAB software. To consider the nonlinearity of the cores, an equivalent magnetization B-H curve is used in the circuit simulation. In order to verify the circuit analysis, field-circuit coupled simulation is integrated in ANSOFT and a PMFCL prototype is further investigated. All of the computed and experimental results have been compared to each other. Field-circuit coupled simulation and experimental measured results confirmed the accuracy of the equivalent magnetic circuit analysis in both normal and fault conditions. The proposed method of magnetic circuit analysis is convenient for mutual influence research of the PMFCL with power systems.