Superconducting power cables: Both technological push and demand pull are needed to spur progress in superconducting, supercooled cables

The time is 1995. Three parallel underground 230-k V circuits, each with three identical superconducting ac cables " one for each phase " are carrying about 10 000 MW of electricity from an energy park into Philadelphia. The park is on the Susquehanna River some 106 km to the southwest. The route traverses farmland, suburban areas, and, in its last 10 km, a densely populated urban area. Helium refrigeration keeps the temperature within the cables at 6.5 to 8.5 K, enough to maintain superconductivity, or zero electrical dc resistance.