This paper describes a study on the optimal location of a resistive superconducting fault current limiter (SFCL) applied to an electric power grid. The resistive SFCL, which is designed to provide the quick system protection in the event of a fault, can have different effects on the planning and operation of a power system depending on its location.To select the optimal location of the SFCL, the sensitivity analysis of power changes and/or power losses in the system with respect to its resistive value occurred in series with a transmission line during a fault is introduced. Moreover, the optimal location determined by the proposed method is coordinated with the corresponding optimal resistive value of the SFCL to improve low-frequency oscillation damping performance of the system. The IEEE benchmarked four-machine, two-area test system is used to evaluate the effectiveness of the proposed method with the case studies based on time-domain simulation.Index Terms-Electric power grid, low-frequency damping, optimal location, sensitivity index, superconducting fault current limiter.

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This paper describes a study to determine the optimal resistance of a superconducting fault current limiter (SFCL) connected to a wind-turbine generation system (WTGS) in series considering its protective coordination. The connection of the WTGS to the electric power grid may have serious effects on the stability and reliability of the overall system during a contingency due to the increase in fault currents. Moreover, it causes malfunction in the protective devices such as overcurrent relays (OCRs). To deal with this problem, the SFCL is applied to reduce the level of fault current increased by the connection of the WTGS. Then, to determine the optimal parameter of the SFCL, protective coordination between the existing multiple OCRs is considered based on the computation of fault current by the equivalent voltage source method.The effectiveness of the optimal resistance for the SFCL is evaluated by the time-domain simulation with the power systems computer aided design/electromagnetic transients including DC (PSCAD/EMTDC) software. The results show that protective coordination is well maintained without changing the previous settings of existing OCRs by applying the SFCL with its optimal parameter. Therefore, the system can keep its suitable reliability even when the level of fault current is increased by connecting the WTGS to the power system. Index Terms-Equivalent voltage source method, overcurrent relay, protective coordination, short-circuit current, superconducting fault current limiter, wind-turbine generation system.

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-This paper proposes the new adaptive protection algorithm for inverse-time overcurrent relays (OCRs) to ensure their proper operating time and protective coordination. The application of the proposed algorithm requires digital protection relays with microcontroller and memory. The operating parameters of digital OCRs are adjusted based on the available data whenever system conditions (system with distributed generation (DG)) vary. Moreover, it can reduce the calculation time required to determine the operating parameters for achieving its purpose. To verify its effectiveness, several case studies are performed in time-domain simulation. The results show that the proposed adaptive protection algorithm can keep the proper operating time and provide the protective coordination time interval with fast response.