Improved Fault Current Limiting Characteristics of Three-Phase Transformer Type SFCL with Non-Separated Secondary Windings due to Unsymmetrical Ground Fault Types

The fault current limiting characteristics of three-phase transformer type superconducting fault current limiter (SFCL) with non-separated secondary windings, which were wound on three legs of an E-I iron core together with three-phase primary windings and were connected with superconducting modules (SCMs), were analyzed due to unsymmetrical ground fault types. The non-separation of three-phase secondary windings was analyzed to play a main role to improve its fault current limiting operations from the viewpoint of the magnetization current and the quench occurrence of superconducting modules (SCMs) especially in unsymmetrical ground faults. To verify its effective operation, the unsymmetrical ground faults such as single line ground and double line ground faults were applied into three-phase power simulated system with three-phase transformer type SFCL with non-separated secondary windings as well as separated secondary windings. From the analysis on three-phase ground fault tests, the power burden in magnetization inductance comprising three-phase transformer type SFCL was confirmed to be more reduced through the balance of power burden between three SCMs compared to the SFCL with separated secondary windings, especially in the case of unsymmetrical ground fault.