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Three-phase transformer type superconducting fault current limiter (SFCL) using two common connection points between secondary windings, which consisted of three-phase transformer windings wound on three legs of E-I iron core and two/three superconducting modules (SCMs), were suggested and its fault current limiting operations according to ground-fault types were analyzed. To verify the effective operation of the three-phase transformer type SFCL using two common connection points between secondary windings, the unsymmetrical ground and the symmetrical ground faults were applied into three-phase power simulated system with the suggested SFCL. For the comparison, the ground faults were generated into three-phase transformer type SFCL with two/three SCMs. Through analysis on the test results, the SFCL with two SCMs was confirmed to have no different fault current limiting operation from the SFCL with three SCMs. The structure of E-I iron core with three magnetically coupled legs and the constitution of three secondary windings with two common connection points were analyzed to be contributed to the same fault current limiting operation. Furthermore, the power consumption and the joule energy of the SCMs comprising both the SFCL with two SCMs and the SFCL with three SCMs during the fault period had shown to be almost the same except for the transient period due to the quench time difference in case of the single-line ground fault.

In this paper, the transformer type superconducting fault current limiter (SFCL) with two nonisolated secondary windings was suggested and its peak fault current limiting characteristics were analyzed. The suggested transformer type SFCL largely consists of two high-TC superconducting elements, one primary winding, and two nonisolated secondary windings, which are wound on the same iron core. Except for the structure with nonisolated secondary winding, the suggested transformer type SFCL has the similar operation to the previously reported transformer type SFCL with two triggering current levels. However, its peak fault current limiting characteristics are different from the previous transformer type SFCL. To confirm its peak fault current limiting operation with two limiting operational currents, the fault current limiting tests of the suggested SFCL according to the fault angle, which affects the amplitude of the initial transient fault current, were performed and its peak fault current limiting characteristics were discussed.

In this paper, the transformer-type superconducting fault current limiters (SFCLs) with common connection point between two secondary windings, which was similar structure to the previously suggested transformer-type SFCL with two triggering levels, was proposed and their current limiting characteristics were compared. The suggested transformer-type SFCLs consist of the primary winding and two secondary windings with common connection point. However, the current limiting operations through two triggering levels, which can be generally adjusted by the winding direction and the number of turns between two secondary windings, are affected by the application position of two high- ${\rm{T}}_{{\rm{C}}}$ superconducting (HTSC) elements into the transformer type SFCL with common connection point. To analyze the dependence of the current limiting operation on the application position of two HTSC elements, the short-circuit tests for the transformer-type SFCL with two different positions of two HTSC elements were carried out and their current limiting characteristics were compared from the point of view of the power burden and the accumulated energy of two HTSC elements comprising each transformer-type SFCL.

In this paper, the transformer-type superconducting fault current limiter (SFCL) with additional circuit, which could limit the fault current through twice quench operations, was suggested. The suggested SFCL includes one primary winding, two nonisolated secondary windings wound on the same iron core, and two high- TC superconducting elements connected with each secondary winding. The advantage of the suggested SFCL is that it can perform the twice current limiting operations due to the transient amplitude of the fault current. Among its design parameters, the winding direction of another secondary winding comprising the additional circuit of the transformer-type SFCL or the nonisolated secondary winding is expected to affect its fault current limiting characteristics. To analyze the dependence of the fault current limiting operation on the winding direction of two nonisolated secondary windings, two limiting operational currents from its electrical equivalent circuit were derived. Through the fault current limiting tests for the suggested SFCL, the fault current limiting characteristics of the SFCL were discussed.

Superconducting fault current limiters (SFCLs) are emerging as an alternative to limit fault current in AC and DC power systems. SFCLs can perform faster current limiting operation and automatic fault current detection and recovery, regardless of the type of fault. In this paper, a laboratory-scale prototype SFCL was fabricated and analyzed for its magnetization characteristics due to the magnetizing current according to the change of the number of windings in pairs. This bridge type SFCL consists of two windings and two high-Tc superconducting (HTSC) elements on one iron core. When the number of windings of the two coils were changed in pairs, the variation of the induced voltage and Joule losses due to the magnetizing current, magnetic flux in each winding, and power losses for the bridge type SFCL were compared with each other. Through comparative analysis, it was confirmed that the size of the number of turns should be considered to reduce the power losses of SFCL while effectively limiting the fault current during the fault cycle.

We report the increase of the current limiting capacity of SFCLs by using the basic 1 × 3 matrix module with 3 superconducting elements. To do this, we fabricated the basic superconducting module with the 1 × 3 matrix structure which consists of a trigger part and current limiting parts. Firstly, we analysed the current limiting characteristics of the basic superconducting module with the 1 × 3 matrix structure. Secondly, we investigated characteristics about the increase of the current limiting capacity of 2 × 3 matrix-type SFCLs and 3 × 3 matrix-type SFCLs which were connected in parallel with 2 or 3 basic 1 × 3 modules. From this procedure, we approved that the easy increase of the current limiting capacity of SFCLs could be realized throughout the simply parallel connection of basic 1 × 3 modules without complex wiring. We used YBCO superconducting thin films and constructed matrix-type SFCLs by using 9 superconductors and 3 reactors. Experimental results were reported in terms of the increase characteristics of the limiting capacity for fault currents and fault voltages.

The flux-lock type superconducting fault current llmiter (SFCL) uses the magnetic coupling between two coils connected in parallel with each other. This SFCL has the merit that both the resistance of high-TC superconducting (HTSC) element and the limiting current capacity can be simultaneously increased through the application of magnetic field into HTSC element. However, like other type of SFCLs using an iron core, unless the saturation of the iron core in the design is considered, the actual limited fault currents can be higher than expected as the saturation of the iron core occurs, and can lead to damage the electrical equipment of the power system. To analyse the dependence of the fault current in the flux-lock type SFCL on the fault angles, its electrical equivalent circuit with the magnetization branch was derived. From the electrical equivalent circuit, the fault current and the inner magnetic flux considering the fault angles as well as the design parameters such as winding direction and inductance ratio of two coils were calculated. The analysis results were compared with the experimental ones, and both the results agreed.