Recovery Characteristics of GdBCO Superconducting Tape With Cooling Fins and Teflon Coating for Resistive Fault Current Limiter

Recovery time, which is defined as the time during which the superconducting component recovers to its initial condition after the current-limiting operation, is very important to design an SFCL. In this paper, the cooling properties of GdBCO superconducting tape with various types of fins or PTFE (polytetrafluoroethylene:Teflon) coating were investigated. Superconducting tape was heated by current, which was larger than its critical current, in liquid nitrogen. The cooling down speed after the current shut down from film boiling to nonboiling and to the superconducting state was investigated. To clarify the effect of surface condition on the heat transfer characteristics, the superconducting test tapes with various shaped fins or PTFE coating were compared with that without fins/coating. According to the experimental results, it was confirmed that superconducting tape with fins or PTFE coating recovered to the superconducting state faster than that without fins/coating and is hopeful for the cooling design of SFCL

Improvement of Recovery Characteristics of REBCO Tape With Several Surface Conditions for Resistive Fault Current Limiter

Superconducting fault current limiters (SFCLs) are required to return to the superconducting state within the proper time (recovery time) after limiting a fault current according to a relay operation scheme in a power system. In order to apply SFCLs to power systems, the recovery time is important property and deeply depends on the heat transfer property of the heated surface of the superconducting tape (normal conducting state) to liquid nitrogen. It has been confirmed that REBCO tapes with various shaped fins or PTFE coating improved cooling property. In this paper, to clear the mechanism of cooling property improvement of fins or PTFE coating, boiling phenomena on REBCO tapes with some types of fins or PTFE coating was observed by use of a high-speed video camera. The influence on the cooling improvement property of cooling fins and PTFE coating was discussed according to the photographical view of the boiling phenomenon