Temporal resistance variation of the second generation HTS tape during superconducting-to-normal state transition
BackgroundThe quench process in high-temperature superconducting (HTS) wires plays an important role in superconducting power devices, such as fault current limiters, magnets, cables, etc. The superconducting device should survive after the overheating due to quench.MethodsWe studied the evolution of the resistance of the YBCO tape wire during the quench process with 1 ms time resolution for various excitation voltages.FindingsThe resistive normal zone was found to be located in a domain of about 1-4 cm long. The normal state nucleation begins in 40-60 ms after voltage is applied across the HTS tape. In subsequent 200-300 ms other normal state regions appear. The normal domain heating continues in the following 5-10s that results in a factor of 2–3 increase of its resistance.ConclusionsFormation of the normal domain during the quench process follows the same stages for different excitation voltages. Characteristic domain sizes, lifetimes and temperatures are determined for all stages.
Normal domain temperature profile in second generation HTS tape wire
BackgroundStudies of the normal zone in high-temperature superconducting wires are extremely important for power applications, such as fault current limiters, motors, cables etc. We studied the temperature distribution and normal domain propagation in high-temperature superconducting YBCO tape with highly resistive substrate.FindingsFor applied voltages exceeding a certain threshold value the normal domain was found to become unstable and started to propagate along the tape.ConclusionsThe normal domain in superconducting tape with highly resistive substrate appears when voltage is applied to the sample.At voltages greater than the threshold value, the domain starts to move.This motion enables us to find the domain temperature and potential profile.
Investigation of the Stability Behavior of Coated Conductors
Superconducting applications like cables, current leads and high current power lines made with YBCO coated conductors (CC) require a protection of the CC against overheating in case of over currents. One possible protection of the CCs is the application of a highly conductive stabilization layer, such as electroplated Cu. The duration of over currents can vary between microseconds and several seconds depending on the application of the superconductor and the characteristics of the fault current. If liquid Nitrogen (LN2) is used as coolant, the transient heat transfer into the coolant varies from adiabatic behavior at short term over currents up to a nearly static heat transfer into the coolant at long term over currents. The thermal behavior of CC cooled by LN2 during over currents was investigated experimentally. The time to reach the transition temperature was calculated analytically and measured for different currents and different stabilizer conditions on the CC. To allow a comparison of the stability for different CCs, a stability number is introduced.