Investigation of cryogenic current leads for contact-cooled superconducting fault current limiters

MINIATURA 5

Funding Organization: National Science Centre

Project title: Investigation of cryogenic current leads for contact-cooled superconducting fault current limiters

Agreement number: DEC-2021/05/X/ST7/00635

Project implementation period: 03.11.2021 - 02.11.2022

Principal Investigator:  dr hab. inż. Michał Majka

Project value: 49 949,00 PLN

Funds granted for Lublin University of Technology: 49 949,00 PLN

Abstract: In the scientific project, research is conducted on the electrical current leads for superconducting fault current limiters.  The research is carried out in the discipline of automation, electronics, and electrical engineering. The current leads connect external devices operating at room temperature with superconducting electrical devices operating at cryogenic temperatures. The warm end of the current lead connected to the power source is at room temperature (293 K), the cold end of the current lead connected to the superconducting device operates at cryogenic temperatures (< 120 K). The power losses occurring in the current leads are about 30 - 50% of the total power losses in the cryostat. Reducing losses in current leads is crucial in reducing cooling costs, significantly influencing the operational stability of superconducting devices and reducing the operating costs of superconducting devices. So far, several methods have been developed for the selection of geometrical parameters of current leads cooled by gas vapour or cryocoolers. However, these methods have been developed for systems supplying superconducting electromagnets. Many superconducting electromagnets are operated at full operating current only for short periods of time, and most often they are operated at the reduced operating current or are kept in standby mode for long periods of time. In the case of superconducting current limiters, we are dealing with different operating conditions for current leads. Under normal grid operating conditions, the rated current flows through the current leads and the current limiter, but under short-circuit conditions, the flow of short-circuit current with a value several times higher than the rated current causes very rapid heating of the current leads to very high temperatures. Other operating conditions of current leads in superconducting current limiters make it necessary to develop new methods of calculating geometrical parameters of current leads for current limiters. The aim of the project is to perform experimental investigations of copper current leads cooled by cryocoolers. The measuring system consists of a vacuum cryostat and a Sumitomo RDK-408 cryocooler with a CSW-71 helium compressor with a cooling power of 34 W on the first stage at 40 K. Experimental investigations will allow the determination of the maximum allowable current value for the current leads at different operating temperatures and the determination of the optimum geometrical dimensions of the current leads to minimizing energy losses in the current leads.