Method and device for cooling of a superconducting cable and corresponding system

A method for cooling a superconducting cable (1) using a coolant comprising liquid nitrogen, the method comprising:

• subjecting at least a part of the coolant to a subcooling step and thereafter bringing the at least a part of the coolant into thermal contact with the superconducting cable (1) in a cooling cycle,
• wherein said subcooling step is at least in part performed using a refrigerant which is provided in a Brayton process in which at least a part of the refrigerant is cooled and heated in a main heat exchanger (11) and a part of the coolant is withdrawn from the cooling cycle, expanded using an expansion valve, and heated in the main heat exchanger (11) in which at least a part of the refrigerant is cooled and heated in the Brayton process, before being vented to the atmosphere, and
• wherein the coolant in the cooling cycle is passed through one or more circulation pumps (2), thereafter subjected to said subcooling, thereafter brought into said thermal contact with the superconducting cable (1), and thereafter recirculated to the circulation pump (2), and
• wherein said part of the coolant which is withdrawn from the cooling cycle and heated in the main heat exchanger (11) is:
• (a) withdrawn from the cooling cycle downstream of said thermal contact with the superconducting cable (1) and before being recirculated to the circulation pump (2),
• (b) withdrawn from the cooling cycle downstream of the circulation pump (2) and before being subjected to said subcooling, or
• (c) withdrawn from the cooling cycle after a part of said thermal contact with the superconducting cable (1).