Role of Insulation Materials and Cryogenic Coolants on Fault Performance of MW-Scale Fault-Tolerant Current-Limiting Superconducting Transformers

Fault-tolerant current-limiting (FTCL) high-temperature superconducting (HTS) transformers are promising components for playing a role in renewable energy integrated modern power systems. In this article, the impact of different insulation materials and cryogenic coolant fluids on the electro-thermal characteristic of an MW-scale FTCL-HTS transformer is investigated. For this purpose, an equivalent circuit model (ECM) is established to characterize the temperature, recovery time, and fault tolerability of FTCL-HTS transformer under different conditions. The proposed ECM is firstly validated using experimental results of a typical HTS transformer. After that the model is developed for a 50 MVA, 132 kV/13.8 kV HTS transformer. In order to add fault tolerance capability to the 50 MVA HTS transformer, three strategies were considered in this article. In the first strategy, the effect of three insulation materials (including Kapton tapes, Nomex papers, and Acrylated Urethane solid insulation) covering HTS tapes was investigated on fault performance. The second strategy was changing cryogenic fluid to liquid hydrogen instead of liquid nitrogen. As for the last strategy, the impacts of thickness and material properties of stabilizer in HTS tape were investigated on the maximum temperature and recovery time of HTS transformer. Results show that by using these strategies, the maximum temperature of HTS tape of transformer winding under a short circuit fault was reduced.