Analysis of Recovery Time of HTS Tapes With Electrical Insulation Layers for Superconducting Fault Current Limiters Under Load Conditions

The implementation of superconducting fault current limiters (SFCL) in the electrical power system requires the coordination of its parameters with the installed power system protection (PSP), in particular when using automatic reclosing (AR). The crucial parameter for AR is the recovery time of the SFCL, understood as the SFCL return time to the superconducting state after its operation. This time will depend mainly on the efficiency of the cooling system and the heat dissipation processes in the electrical insulation system. This article presents the results of experimental research on the return time to the superconducting state of superconducting tapes with layers of electrical insulation of various thicknesses. The tests were carried out in conditions in which the density of energy generated during the surge current flow correspond to the operating conditions of superconducting material in SFCL. Also, the transfer of this energy to liquid nitrogen corresponds to phenomena occurring in SFCL. The recovery time of several types of high temperature superconducting tapes in the zero current state and recovery under load were determined. The range of the load current at which it is possible return to the superconducting state was determined for tapes with and without electrical insulation. It has been shown that the analysis of these processes must take into account the strong dependence between the thermal energy transfer from the sample surface to liquid nitrogen and the type of nitrogen evaporation process on the surface of the sample. The presented research results are of particular importance for the functionality of SFCL and its cooperation with the PSP.