Short circuit analysis of a fault-tolerant current-limiting high temperature superconducting transformer in a power system in presence of distributed generations

Power transformers are key elements for the safe and reliable delivery of electrical energy generated by renewable energy resources to consumers via transmission lines. Fault-tolerant current-limiting High Temperature Superconducting (FTCL HTS) transformers are type of superconducting transformers that tolerate fault for seconds and limit the fault current without the threat of burnout or delamination of tapes and deformation of windings. In this paper, the fault performance of a FTCL HTS transformer in a standard IEEE power system is investigated. The studied transformer is a 50 MVA 132 kV/13.8 kV transformer where both windings are made up of HTS tapes. The understudied power system consists of two microgrids with distributed generators. Part of the power in microgrids is supplied by the upstream grid which is connected to the microgrids through the HTS transformers. Two fault scenarios have been considered in this power system, in each one of these scenarios, a fault happens in one of the microgrids. Two considered fault scenarios have an approximate fault current of 18x to 23x of the rated current in the secondary windings. Results showed that insulated windings in FTCL HTS transformers could substantially reduce the peak temperature of the HTS windings, compared to bare windings. Afterwards, post-fault loading is imposed on the HTS windings, to observe their performance against the current increase after fault clearance. In this case, for the first scenario of the faults, the FTCL HTS transformer could tolerate 192% of post-fault overloading, while this number for the second fault scenario is 170%. Finally, the impact of post-fault loading on the full recovery time was discussed.