The Field Decay Characteristic for a Closed HTS No-Insulation Coil With Partial Tape Exposed to an AC Magnetic Field

No-insulation (NI) coils made by second-generation (2G) high-temperature superconducting (HTS) tapes have a better thermal stability than traditional coils which wound with insulation. The NI coils have been developed and been employed in many superconducting applications such as superconducting motor, transform, and generator. In these cases, the NI coils will inevitably be affected by ac magnetic field. When a superconductor carrying a dc current is exposed to an ac field, a dynamic resistance
R
_dyn
will occur and cause significant ac loss. In this paper,
R
_dyn
is calculated by field-decay method, which has a wider measurement range and higher accuracy than four-probe method. The correction curve for
R
_dyn
with the ratio of operating current and critical current (
I
_op
/
I
_c
) is presented. Combining the persistent-current mode (PCM) circuit model of closed NI coil and the correction curve, a predictable simulation model for central magnetic field characteristic of closed NI coil with partial tape exposed to an ac magnetic field is established and verified by experiments.