Novel gases as electrical insulation and a new design for gas-cooled superconducting power cables

摘要

High Temperature Superconducting (HTS) power cables are being developed for a variety of applications including the electrical power grid, electrification of transportation, and high energy physics. The appeal of superconducting technology is its high current density - generally greater than 100 A/mm(2) - compared with conventional copper and aluminum conductors, which generally do not support greater than 5 A/mm(2). Thus, HTS wires and cables support high power ratings even at low and medium voltages, which reduce the size and weight of the electrical power systems. The size and weight reductions are essential to realize large all-electric ships and electric aircraft. HTS devices must be operated within the boundary of their respective critical temperature, critical current, and critical magnetic field [1]. Second generation HTS materials possess critical temperatures of similar to 90 K. However, operating temperatures in the range of 50-70 K are typically required for HTS cables to support the desired operating current of many power-dense systems and to have a sufficient temperature margin to tolerate unexpected heat loads and fault currents. When a superconductor exceeds any of its three critical parameters, a quench will occur. A quench causes the HTS cable to transition to its normal state where it starts to display its high electrical resistance. The interdependency of the electrical and thermal properties of HTS materials also depends on the cryogen used to achieve the desired operating temperature. There are only a few cryogens compatible with the desired operating temperatures of <77 K, with liquid nitrogen (LN2) being the most commonly used for HTS cable applications for the electric power grid due to its abundance, low cost, and good electrical insulation and heat transfer properties. LN2-cooled HTS cables have been successfully demonstrated in the electrical power grid operating at 10-200 kV [2], [3]. The LN2-cooled 10 kV AC HTS cable installed as part of the Ampacity project in Essen, Germany demonstrated the potential of HTS technology to be economically feasible in urban areas. Installing the 10 kV HTS cable instead of a conventional 110 kV cable to supply the downtown area of Essen allowed for 4 out of 10, 110/10 kV transformer substations located in the center of Essen to be decommissioned and removed [2].