Experimental Study for Modified Lumped-Circuit Model to Analyze Saddle-Shaped No-Insulation HTS Coil Operated in Overcurrent Situation

This work presents a modified lumped-circuit model for a saddle -shaped no-insulation (NI) high temperature superconductor (HTS) coil in overcurrent, which is defined by the situation that azimuthal current is close to or greater than the critical current. We suggested the variation of the coil's circuit parameters, such as inductance, 'index' resistance, and characteristic resistance. We modified the base assumptions of the conventional lumped-circuit model and experimented to validate the suggested model. An 82-turn saddle -shaped NI coil was fabricated, and terminal voltage and magnetic field were measured during the overcurrent test in a 77 K liquid nitrogen bath. Compared to the conventional model, our modified lumped-circuit model reduced the error between measurement and simulation from 44.2% to 2.9%. We inversely calculated the variation of circuit parameters and magnet constant, which cannot be the constant value, and the results are presented.