Cryocooler cooled HTS current leads for a 1 MJ/1 MW-Class SMES system

Within the Italian project for the development of 1 MJ/1 MW SMES, Ansaldo-CRIS and CESI have been involved in the design and manufacturing of 1100 A resistive/HTS current leads conduction cooled by a closed cycle refrigerator. Main design and technological problems concern the achievement of electrical insulation between cryocooler and current leads at the voltage level of 6 kV together with a thermal contact good enough to keep the upper part of the HTS material at a temperature below 70 K, when the cryocooler temperature is 60 K and about 100 W is the thermal load. Thermal transport properties of electrical insulating materials as thin sheet placed between copper massive plates have been measured as a function of temperature and hence, according to the measured thermal performances, the area for thermal contact with the cryocooler has been suitably dimensioned. Mechanical structure for the whole current leads has been designed and manufactured. Final assembly of resistive section has been completed. Results about the achieved lead performances are presented and discussed.