How to Speed Up Y–Ba–Cu–O Tape Recovery

The recovery of Y-Ba-Cu-oxide tape, which is intended for use in a resistive fault current limiter, was, in a comprehensive way, related to the radial heat transfer and sample properties. To check our numerical model, experiments were made on a SuperPower tape and a set of copper wires in a liquid nitrogen bath at 77 K. The inner sample temperature
T
(
t
) and radial heat flux density
q
(
T
)
t
were deduced from the
I
(
t
) and
U
(
t
) , which were measured during the sample cooldown, after immersion to the bath. The temperature fall mimicked a zero-current recovery after the quench. The idea of the heat flux measurement was based on the fact that, for a specific sample, which is immersed in a coolant, the enthalpy change
Vocm
ρ
m
(
dT
/
dt
) is in equilibrium with the heat removal
q
(
T
) ·
So
, during the cooldown from initial temperature. Measuring the rate of the enthalpy change at a moment
t
, we measured the radial heat flux across the wetted tape surface
q
(
T
)
t
. For a superconducting tape, the
Tc
presented the lower limit of this method. Still, {
dT
/
dt
}(
t
) allowed tracking the onset and span of the superconducting transition, giving the quick, simple, and cheap way for
Tc
estimation. Moreover, the self-heating burst of the transport current was applied to a sample (both in a numerical model and in experiment). Choosing an appropriate thermal insulation layer on a surface and keeping the thermal capacity/wetted surface ratio small were recognized as the ways of recovery speedup, in parallel with making the volume density of the heat power or the total time of the overall heat load after fault as small as possible (increasing matrix resistance or incorporating protective switch within hybrid scheme).