May 17, 2009

AAC/ACSR Conductors


The Indian Standards Institution has brought out the following specifications on AAC/ACSR conductors. IS: 398-1979 ‘Specification for Aluminum Conductors for Overhead Transmission Purposes’ which consists of three parts. Part 1 details with Aluminum Stranded Conductors: Part 2 with Aluminum Conductors Galvanized Steel Reinforced: and Part 3 with Aluminum Conductors, Aluminized Steel Reinforced.

Aluminum Stranded Conductors

A stranded conductor consists of seven or more aluminum wires of the same nominal diameter twisted together in concentric layers. When the conductor consists of more than one layer, successive layers are twisted in opposite directions. The diameter of the stranded conductor is the mean of two measurements at right angles taken at the same cross section. The direction of lay is considered as right hand when the conductor is held vertically and left hand if they conform to the direction of the central part of the letter S. The lay ratio is defined as the ratio of the axial length of a complete turn of the helix formed by and individual wire in a stranded conductor to the external diameter of the helix.

The conductor shall be constructed of hard drawn aluminum wires having mechanical and electrical properties. When specified by the purchaser, neutral grease may be applied between the layers of wires. The wires shall be smooth and free from all imperfections, such as spill and splits. The aluminum wires for the stranded construction covered by this specification shall have the diameter as per spect. A tolerance of ± 1 per cent shall be permitted on the nominal diameter. There shall be no joint in any wire of a stranded conductor containing seven wires, except those made in the base rod or wire before final drawing. In stranded conductors containing more than seven wire, joints in individual wires are permitted in addition to those made in the base rod or wire before final drawing, but no two such joint shall be less than 15 meters apart in the complete stranded conductor. Such joints shall be made by resistance or cold pressure butt welding. They are not required to fulfill the mechanical requirements for unjointed wires. Joints made by resistance butt welding shall, subsequent to welding, be annealed over a distance of at least 200 mm on each side of the joint.

The wire used in the construction of stranded conductor shall, before stranding, satisfy all the relevant requirements of the specifications. The lay ratio of the different layers shall be within the following limits. When the number of wire is 7, the lay ratio for 6 wire layer shall be between 1 and 19. When number of wire is 19, the lay ratio for 6 wire layer and 12 wire layer shall be between 10 and 16, and 10 and 14, respectively.

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