During an abnormal heat wave in the summer of 1999, the South Fork region of Long Island, New York, U.S., which comprises the towns of Southampton and East Hampton, experienced a 25 percent increase in power demand from the same period the previous year. The increase lasted for days.
The two 69-kV circuits that supply energy to the region, along with several local peaking units, were operating at maximum capacity without reserve. Through immediate conservation measures, brownouts and rolling blackouts did not occur, and the region escaped a potential catastrophe.
After assessing various methods, such as voluntary conservation, distribution automation, local generation and additional transmission supply lines, Long Island Power Authority (LIPA), along with its T&D system manager KeySpan Energy, determined that a new 138-kV underground transmission system would be built. The system extends from LIPA's Riverhead Substation to its Southampton Substation, directly located in the load growth pocket. This distance of the line is about 22.5 miles (36 km).
Engineering and design began in August 1999 and entailed the route design of 22.5 miles of 138-kV solid dielectric 1200 mm2 (2 in2) XLPE cable arranged within 8-in (20-cm) high-density polyethylene conduit. Cable sheath cross-bonding techniques also were engineered to minimize sheath-voltage levels and optimize the cable's current carrying capacity.
The cable route was identified in areas of good thermal resistivity, minimal population density and where limited vegetation trimming and removal would be required. Part of the cable route is canal, where a cable support conduit system will be suspended below the bridge roadway within its steel girder area.