Gas-Cooled Peltier Current Leads for Compact HTS Devices

Abstract

As is known, heat losses through current leads essentially determine the economic efficiency of the superconducting systems. Much attention is paid to the design of optimal current leads, but the Wiedemann-Franz law physically limits the benefits of the standard approach. An innovative way to further reduce heat inflow is to use current leads equipped with Peltier thermoelectric elements. These elements are installed in series in the power circuit. Therefore, when the transport current passes through the Peltier element, the thermoelectric effect counteracts the heat flow caused by the temperature gradient in the current lead. Another advantage of this design is that when the circuit is de-energized, the heat loss is reduced due to the low thermal conductivity of the Peltier element. In addition to the theoretical works devoted to the Peltier current leads (PCLs), many experiments confirmed a decrease in heat loss by about 30%. Moreover, PCLs were installed on 500- and 1000-meter HTS power transmission lines in Ishikari (Hokkaido, Japan). An advanced approach involves cooling the current-carrying parts with evaporating nitrogen, which should improve the performance of PCLs. In this work, an experiment on testing gas-cooled PCLs was carried out for the first time. A 30% additional reduction in heat inflow was achieved. At the same time, the dependence of the specific heat loss on the current became flatter, which means an expansion of the range of operating current. In the experiment, the vented gas passed through copper pipes used as conductors. In the future, to increase the efficiency of the gas-cooled PCLs, we plan to improve the heat transfer between the gas flow and the conductor using surface ribbing.