Improving the performance of saturated cores fault current limiters by varying winding density in the AC coils

Effect of the winding density in the AC coils on the performance of a saturated cores fault current limiter (SCFCL) has been studied, exploiting Finite Element Analysis. For a given design, a fixed number of turns was concentrated at the center of the AC coils limb, resulting in high windings density. The coil length was then increased gradually along the limb, decreasing the winding density and therefore decreasing the coil impedance. However, we found that the ratio between the fault to nominal state impedances increases with decreasing winding density. The results are discussed and explained as originating from the change in the flux linkage of windings in the coil for various core states. In the nominal-state of the SCFCL, the core is saturated and the coupling between the windings is lower, given the lower winding density. However, when the core is desaturated during a fault, the magnetic interaction of the windings with the core strengthens, the coupling between the windings increases and contributes to higher fault-state impedance. Thus, reducing the winding density may serve in increasing the impedance ratio of the device and improving the performance of SCFCLs. The results suggest that the windings density in SCFCLs should be used as a significant design parameter.