Current Limitation Experiments on a 1 MVA-Class Superconducting Current Limiting Transformer

We designed, built, and tested a single phase 577 kVA transformer demonstrator, optimized for high current limiting capability and low loss operation. The transformer demonstrator consists of a conventional warm iron core and a normal conducting primary winding operated at 20 kV / 28.9 A in combination with a superconducting secondary winding at 1 kV / 577.4 A composed of 12 parallel ReBCO-tapes. To demonstrate the short-circuit behavior we present in detail a current limitation experiment. The results show that the current limiting transformer design is capable of limiting short-circuit currents in the first half-wave of a fault to 67.6% and in the sixth half-wave to 29.1% of the prospective current. The current distribution among the parallel tapes was analyzed and showed different current sharing patterns for the nominal transformer operation and during the current limitation. The experimental results are further compared to numerical simulations to predict the current limitation behavior under short-circuit conditions with parameters different to the conducted experiments. In addition to the successful current limitation, we also present and explain a mechanism during a current limitation measurement that lead to a failure of the superconducting winding of the transformer demonstrator. The reason for this failure is discussed and we give a recommendation for changes in the transformer design to prevent similar failures in future generations of superconducting transformers.