Analysis of heat transfer characteristics of (6+1)-structure MgB2 cable

Abstract

$\mathrm{Mg}{B}_2$ superconducting material has a wide range of application prospects for its high transition temperature, favorable structural characteristics and low cost. When using $\mathrm{Mg}{B}_2$ to produce superconducting energy storage magnets, it is necessary to twist superconducting wires into cables to increase their current carrying capacity. One typical cable is made of 6 $\mathrm{Mg}{B}_2$ superconducting wires wrapped around 1 central copper wire, forming a (6+1) structure. $\mathrm{Mg}{B}_2$ coils used for energy storage require solid impregnation and can be cooled by liquid hydrogen or solid nitrogen. Due to the need for fast charging and discharging of energy storage coils and low thermal conductivity of commonly used epoxy resin impregnation and solid nitrogen, it is necessary to consider the temperature variation characteristics caused by AC loss and eddy current loss during operation process. A coil with 8 turns in each layer and 4 layers is simulated using the (6+1)-structure cable. In order to obtain better temperature distribution results while reducing the time required for simulation operation, the simulation time is set to 1 s. The impact of epoxy resin properties and surrounding environments on the coil are then analyzed. The results indicate that increasing the thermal conductivity of epoxy resin can significantly reduce the maximum temperature of the coil, while only changing the cooling method is unhelpful in dealing with the problem of local overheating of the coil.