Coated conductor arrangement for reduced AC losses in a resistive-type superconductingfault current limiter

Abstract

The basic element of a resistive superconducting fault current limiter (FCL) can consist ofcoated conductor tape exceeding a few meters in length and compacted into a cryogenicenvelope. This paper is focused on optimizing the arrangement of coated conductors with anon-magnetic substrate for a resistive superconducting FCL. Several configurations havebeen tested experimentally and theoretically. Two low-loss arrangements have beenidentified, both utilizing the bifilar configuration, i.e. the currents in two adjacent tapes areidentical in amplitude but opposite in direction. The separation between two adjacent tapess varied from 0.07 up to 2.10 mm. For the lowest examined separations the AC transport loss of the straight bifilar model decreased by more than one order withrespect to the AC transport loss in the single-tape configuration. Further AC loss decreaseis achieved when the pair of tapes carrying opposite currents forms a flat pancake coil. Wedeveloped a numerical model in order to analyze the influence of distance between adjacenttapes. To achieve agreement between experimental and numerical results it wasnecessary to incorporate a lateral distribution of critical current density in the tape.The remaining differences between the results of experiment and calculation canbe explained by analysis of experimental imperfections. Finally we suggest anempirical fit for the prediction of AC loss of a practical superconducting fault currentlimiter.