Determining the Operating Current of No-Insulation Field Coils in HTS Generators

This paper proposes a new method for calculating the operating current of high-temperature superconducting (HTS) no-insulation coils whose overcurrent characteristics are more stable than those of conventional field magnets in superconducting generators. Problems related to calculating the operating current of conventional high-temperature superconductors have been analyzed, and the conditions for coils to overcome such problems have been proposed. To complement electrical stability issues of conventional HTS field coils, a small pancake coil was constructed from the Bismuth strontium calcium copper oxide (BSCCO) first-generation HTS wire with noinsulation winding. The pancake coil was then tested. The tests confirmed that the no-insulation coil was electrically stable. In addition, it was confirmed that quenching did not occur in electrically stabilized coils, even at higher input currents than the critical current value of the coil. In addition, the magnetic field value having the largest effect on the decrease in the critical magnetic field in the superconducting coil was calculated through finite-element method analysis, thus predicting the effective current of the superconducting coil. This analysis was compared with experimental results to demonstrate the validity of the proposed method.