Study on heat transfer characteristics of stainless steel wrapped YBCO strip under liquid nitrogen

Abstract

This paper mainly studies the heat transfer characteristics of stainless steel wrapped YBCO strip in the resistance superconducting current limiter under liquid nitrogen, and provides theoretical basis for the design and manufacture of superconducting current limiter through the study and comparative analysis of its electrical and thermal properties under out-of-state state.Based on the experiment, the characteristic curve of superconducting strip itself is established. On this basis, the temperature distribution of epoxy curing coil and non-epoxy curing coil in liquid nitrogen with different heat transfer coefficients and impact current is studied. For the superconducting strip without epoxy curing, the loss of superconductivity instantly generates a large amount of heat to conduct outwards. If the coil is directly in contact with liquid nitrogen, it will produce boiling phenomenon and quickly produce a large amount of gas. For different currents, the superconducting strip will eventually reach thermal equilibrium at different temperatures. The higher the current, the higher the thermal equilibrium temperature. Through simulation analysis, the current is controlled at 5 times Ic, the superconducting strip surface is in the state of nuclear boiling, and the temperature transfer is faster. The energy efficiency of the high-temperature superconducting coil cured by epoxy can limit the heat output, the heat conduction rate decreases, the coil cooling rate is slow, and the temperature difference between the surface of epoxy-liquid nitrogen decreases, and the boiling phenomenon is restrained to some extent. In this process, the heat transfer is less, which can be approximated as an adiabatic process, but the coil's tolerance time is only about 0.15s, beyond this time, the coil temperature is too high and easy to burn. In epoxy curing coil, different epoxy layer thickness has a great impact on subsequent quench recovery time. The epoxy layer thickness increases from 0.01mm to 0.2mm, and the time rapidly increases from 0.5s to 3s. If epoxy is used for curing, if the system does not consider the recovery time, epoxy can be used as thermal buffering material, but if the heat is generated too fast to be released, and the temperature exceeds the bearing limit of epoxy and strip, the strip will be damaged.As the performance of the current superconducting strip is fragile, it is a bottleneck problem in the current limiter. In order to protect the superconducting strip, in the design and manufacture of the current limiter, the scheme without epoxy curing coil is preferred.