GB1151412A - Improvements in or relating to Overhead Electric Transmission Systems - Google Patents

Abstract

1,151,412. Transmission systems; protective arrangements. BRITISH INSULATED CALLENDER'S CABLES Ltd. 6 Sept., 1967 [7 June, 1966], No. 25351/66. Headings H2C and H2H. In an overhead transmission system having one or more earth wires 5 (25) (Fig. 5, not shown) strung above the line conductors 4, the uppermost part 6 of each or some of the support structures is made of insulating material and at the support structure the earth wire is connected to earth by a conductor 7 through a resistor 8 having a resistance equal (or approx. equal) to the characteristic impedance of the conductor, which resistor is wholly or partly embedded in the ground so that a lightning current wave will not flash across it to earth. There may be vertical structure extensions 9 to maintain the characteristic impedance of the conductor which may be secured by insulating braces 10, (30) (Fig. 5, not shown), which, together with parts 6, may be of resin bonded glass fibre. The earth conductor may be adjacent to, but outside the support structure (Fig. 3, not shown) and lie in the vertical plane of the earth wire. The support may be an H-pole structure (Fig. 5, not shown) where the conductor is in a vertical plane between the two earth wires. The conductor may be circular or annular, solid or stranded, or folded from a strip to be annular and have an insulating covering. It may be the central conductor of a coaxial cable, the outer conductor being connected to the support structure or earthed. The resistor may be a rod of SiC and may have a resistance of 50#.