  The current-voltage characteristics of superconductors are commonly
determined by means of a standard 4-probe DC measurement technique. In coated
conductors, however, one often encounters problems due to weak or no
stabilization and in such case, when the risk of burning the tape is high, the
4-probe approach can fail. In other cases such as in HTS cable structures,
besides vulnerability and high risk of damage, it may also be difficult to
achieve a high critical current level with a power supply that is normally used
to characterize single strands. We therefore investigated an alternative method
to determine the DC I-V curve, based on measuring the AC transport loss as a
function of frequency in overcritical current range. In the AC regime, both the
hysteretic loss component and the joule dissipation are present for applied
transport currents exceeding the critical current Ic. In this work, AC loss
measurements at different frequencies are related to different electric fields
in DC and a curve similar to the DC I-V is obtained. From this curve, the power
index N and Ic values are estimated. AC regime operation can be more beneficial
for two reasons: firstly, because very high currents can be achieved easily by
using a transformer; secondly, because the effective joule heat dissipation
with overcritical AC currents is much lower than that with DC of the same
amplitudes. In the experiment, we used a 4 mm wide YBCO reference tape with 20
{\mu}m of Cu-stabilization. For the comparison with AC transport loss, the
sample was measured with the standard 4-probe technique and remained stable
even in overload condition. To support our study, numerical simulations,
reproducing both transient and stationary operation conditions, were performed.
A similar relation between the AC current transport loss and the I-V curves was
also observed in the simulations.
