Current-Sharing Behaviour of Single-Phase HTS Transformers With Stacked-Tape Cables

The performance of HTS transformers is integral to predictability of outputs in HTS transformer-rectifier flux pumps. To date, little attention has been given to compact HTS transformers using stacked-tape cables. Current sharing behaviour in HTS transformers with stacked-tape cable secondary windings is studied here experimentally. Secondaries of 1-4 tapes are tested with a 500:1 transformer. Two modes of coupling are identified. Firstly, primary inductive coupling determines secondary current during changes in primary current. Secondly, current is shared inductive between loops when primary current is held constant. This is caused by secondary circuit resistance. The transition between sharing modes causes strong hysteresis in the current output of the transformer. However, this is found to have little impact on the RMS current in the secondary if the resistance is sufficiently low. Outputs greater than 600 A are demonstrated from a compact transformer. These results may lead to more compact transformers in future transformer-rectifier flux pump devices.