Design and Experimental Evaluation on kA-Class HTS Binary Superconducting Current Lead Using a Liquid Nitrogen Bath under Short-Term Current Test

A power supply located at room temperature is normally connected to superconducting machines through a pair of current leads. The current leads should carry currents along a range of temperatures from 4.2 to 300 K with low heat load to minimize cooling power required to cool the whole current lead at operating conditions. Heat loads into the magnet cryostat through these leads are responsible for most of the running cost of the magnet system. In this paper, an alternative size optimization is described for a binary current lead consisting of a liquid nitrogen vapor-cooled resistive heat exchanger (first stage) and a high temperature superconducting part (second stage). The optimal size was determined where the required liquid nitrogen mass flow at the cold end of the heat exchanger is minimal. Thermal and magnetic self-field analysis was also performed for the second stage of the current lead carrying current in opposite direction. Moreover, the results of the short-term operation of the current leads at 1000 A including the voltage drops across the heat exchanger and the HTS part are presented. The measured data are compared with the calculated temperature profile.