220-Kv. Transmission Line for the Conowingo Development

Current from the Conowingo plant is carried fifty-eight miles to the Plymouth Meeting Substation of the Philadelphia Electric Company over two 220-kv. single-circuit steel-tower transmission lines. These lines are carried on a right-of-way which provides space for a third future line. The conductors are 795,000-cir. mil steel-reinforced aluminum. Each circuit is shielded by two 183,600-cir. mil aluminum steel-reinforced ground wires. The insulator strings consist of 14 high-strength units in suspension position and 16 units in strain position. Conductors and ground wires are carried in a new type of slip clamp in order to decrease the unbalanced longitudinal stresses on the towers in the event of wire breakage. In general, foundations are of the earth grillage type. The tower design includes a number of novel features, among them the use of combination extensions to meet flexibly the varying topographical conditions, and the narrow waist immediately below the basket.