Cool-Down and Thermal Performance Test for Toroidal Configuration HTS SMES

The high-temperature superconducting (HTS) magnetic energy storage system working temperature is around 20 ~ 30 K because the HTS coils must be cooled below the critical temperature. In this paper, we have designed a system with an operating temperature of 15 K or below for the purpose of full utilization of the HTS wire material, minimization of the hardware dimension, and stable operation. For the cooling, four of 2-stage Gifford-McMahon coolers were used. The cooling system has a short and uniform thermal passage from the cryocooler head to each HTS coil for an effective cooling of HTS coils. The cold head first stage cools the thermal shield and current lead, and the second stage cools the HTS coils. Our full system has a total of 28 double pancake coils forming a toroidal configuration. For this study, we assembled a test set consisting of six dummy double pancake coils for cooling and load tests without charging current. This paper describes the cool-down and the thermal characteristics of the conduction cooling system. The modified cooling method is optimized for cool-down time reduction, and thermal tests were performed with heat loads up to 300 W.