Multiobjective Design of Tunable Shield-Type Superconducting Fault Current Limiter

Shield-type superconducting fault current limiters (SFCLs), due to their outstanding advantages, form an important category of SFCLs. Tunable shield-type SFCL is a novel device that introduces the extra advantage of controllable fault current limitation. As different limitation currents may be required in a voltage level of the power system, the tunability characteristic, aside from the unification of devices, may eliminate the need for multiple SFCLs in power substations and result in reduction of total initial and operational costs. In this paper, basic relations governing the operation of the novel tunable shield-type SFCLs are presented and target functions are defined, which have the most impact on the cost, weight, and performance of the device, such as the volume of copper, iron, and superconductor; the maximum control voltage source; and the ohmic resistance and leakage reactance of primary winding. A heuristic method has been proposed for the multiobjective design of tunable SFCLs where weight coefficients are defined to choose the degree of importance of each target function. Eight cases have been studied with various weighting coefficients; the variations of the target functions are compared in these cases. The outputs of the optimization flowchart for one of the cases have been used for the fabrication of a prototype that has shown satisfactory tunable characteristic in limitation current. The experimental test results have shown good compatibility with the theoretical results.