Normal transition and stability characteristics of YBCO coated conductors under AC / pulse operation

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S/N transition processes of monofilament / multifilament YBCO conductors as well as parallel conductors were studied experimentally and numerically, and the following results were obtained.1)Ramp-up currents and AC over-currents were supplied to single YBCO conductors to study their S/N transition processes. It was found that the time-derivative of the supplied currents does not influence the S/N transition processes of single YBCO conductors. In case of AC over-current tests, a normal zone generated near the peak of the supplied current disappeared when the magnitude of the current decreased.2)Two YBCO coated conductors were connected in parallel, and ramp-up currents were supplied to study their current sharing characteristics. Due to different contact resistances to the current lead, some current imbalance was observed in currents of two conductors. When the current of the conductor carrying more current became larger than its critical current, a normal zone was produced, and the current transferred to other conductor to influence their stability property.3)S/N transition processes of monofilament / multifilament YBCO conductors were studied numerically by the combination of the electromagnetic field analysis and thermal analysis using FEM. It was found that the externally applied AC/pulse magnetic field substantially influences the current distribution on YBCO conductors but not substantially influences the temperature distribution and quench characteristics. Longitudinal distributions of critical currents do not substantially influence quench characteristics.