Analysis of the Evolution of Accidental Transients in the Cooling of a MgB ₂ -LH ₂ Hybrid Power Cable

The safe and reliable operation of superconducting cables is critically dependent on efficient cooling strategies, and this point becomes even more relevant when hybrid cables cooled by liquid hydrogen (LH2) considered. This study analyzes the evolution of accidental transients in the cooling of a submarine 30 km hybrid cable in MgB2, capable to transfer 10kA at 30 kV and a mass flow rate up to 1 kg/s of LH<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> at 20 K. Three key failure scenarios are examined: a loss-of-flow accident (LOFA), a loss-of coolant accident (LOCA) and a loss-of-vacuum accident (LOVA). For each of the accidents, the phenomenology leading to the cable cooling deterioration is first discussed and the qualitative or quantitative evolution of the thermal-hydraulic transient in an unprotected situation is presented. The diagnostics most suited to detect the accident are then identified. This work, the first of its kind, suggests instrumentation to detect the occurrence of the different scenarios to protect the investment associated with the future hybrid power cables. The analysis shows that the loss of flow is easy to detect and the operators can reduce the cable power without any loss of LH<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>. The LOCA is more severe, as it requires fast detection that could be achieved using optic fibers, whereas overpressures and opening of relief valves are difficult to avoid especially for large ruptures. The LOVA is the most severe among the accidents investigated here, as it is difficult to detect without optic fibers.