Cryogenic design and test results of 30-m flexible hybrid energy transfer line with liquid hydrogen and superconducting MgB2 cable

Abstract

In this paper we present the development of a new hybrid energy transfer line with 30m length. The line is essentially a flexible 30m hydrogen cryostat that has three sections with different types of thermal insulation in each section: simple vacuum superinsulation, vacuum superinsulation with liquid nitrogen precooling and active evaporating cryostatting (AEC) system. We performed thermo-hydraulic tests of the cryostat to compare three thermo-insulating methods. The tests were made at temperatures from 20 to 26K, hydrogen flow from 70 to 450g/s and pressure from 0.25 to 0.5MPa. It was found that AEC thermal insulation was the most effective in reducing heat transfer from room temperature to liquid hydrogen in ∼10m section of the cryostat, indicating that it can be used for long superconducting power cables. High voltage current leads were developed as well. The current leads and superconducting MgB2 cable passed high voltage DC test up to 50kV DC. Critical current of the cable at ∼21K was 3500 A. It means that the 30m hybrid energy system developed is able to deliver ∼50–60MW of chemical power and ∼50–75MW of electrical power, i.e. up to ∼135MW in total.