HTS cables available today are commonly referred to as “cold dielectric” cables. This description refers to the fact that the dielectric, or electrical insulation, of the cable is located inside the cryogenic cold portion of the cable structure.
Several projects around the world have demonstrated “warm dielectric” HTS cables, but no work in currently ongoing in this area. Warm dielectric cables located the electrical insulation outside the cryogenic cold portion of the cable structure.
Just like conventional cable systems in the utility network, HTS cable systems comprise three electrical phases. Several design options exist to achieve three phases with HTS technology:
Single Phase Cable
Like conventional cables, this option consists of a separate complete cable structure for each phase. Each phase has its own cryostat thermal insulation pipe.
Three Core Cable
This design option is similar to a conventional 3-core gas pressure cable. Three separate phases are constructed as individual cores, which are then twisted together and placed inside a common cryostat thermal insulation pipe. This design has the advantage of a reduced cold surface area versus the single-phase option, reducing the cryogenic cooling load.
HTS Triax Cable
This design places all three electrical phases concentric on a common core, inside a common cryostat thermal insulation pipe. The concentric arrangement of phases allows for a reduction in HTS wire by 50%, significantly reducing overall system costs. It shares the reduced cold surface area advantage with the 3-core option above.