Fault current limiting properties of YBCO-films on sapphire substrates

Abstract

Absraarct -We have studied the switching of YBCO thin film resistive fault current limiting devices. Films of 300 nm thickness were deposited on 2 inch and 4 inch sapphire substrates by thermal co-evaporation. Bridges 10 mm wide and 22 mm long (2 inch) or 42 mm long (4 inch) were structured by standard photolithography. Contacts were made by in-situ gold overlayers and soft solder. The gold film was removed from the switching area so that the YBCO film was not shunted. The films were tested by 30 ps DC pulses and 50 Hz AC pulses for 50 ms. We find evidence that at the AC tests heat propagates over several cm under these conditions in sapphire so that hot spots can be avoided even without shunt layer with the prospect of higher switching power. The highest destruction free switching power -the r m s critical current times r m s voltage after switching -was 57 kVA. The highest switching power density achieved was 2.5 kVAkm2. To our knowledge, these are the highest switching power densities observed so far.

Resistive fault current limiters with YBCO films 100 kVA functional model

“…the nominal power per substrate area, of about 130 W/cmz. Experiments with single switching elements and recent results of other groups [5] indicate that the maximum achievable power density is much higher. This would make the devices even more compact.…”

Switching behavior of YBCO thin film conductors in resistive fault current limiters

“…The jump in resistance starts when the current in the strip is at its peak, which is typically -for epitaxial YBCO films [1], [3]- [5]. The rise is ending as the device starts to limit the current to with .…”

“…A variety of FCL designs have been demonstrated in the last years proving the feasibility of the concept [1]- [5]. The quench process in the first moment of overcurrent condition controls the switching behavior of the thin film conductors.…”

Superconducting FCL: Design and Application

“…Some papers [48] reported that such structures would prevent domains and provide fast propagation of the normal zone. However, recent experiments showed that overheated zones also appear in long thin film elements [39].…”