In a transmission system, cables play a significant role. The various types of cables exist in industry are low tension cables, high tension cables, super tension cable, extra high voltage solid type cables, extra high voltage oil-filled cables and extra high voltage gas pressure cables. The main parts of a cable design point of view are core, insulation, metallic sheath, bedding, armouring and serving. Entry of moisture to insulating material is prevented by metallic sheath. Lead, lead alloy and aluminium can be used as metallic sheath. Bedding is essential for providing a layer of paper tape compounded with a fibrous material or jute strands over the metallic sheath. Both bedding and armouring protects cables from mechanical injury. In the armouring process, cables are provided with layers of galvanized steel wires or layers of steel tape. The insulating materials used for cable are polyvinyl chloride, polyethylene, vulcanized rubber, cross-linked polyethylene cable, varnished cambric, vulcanized bitumen, gutta percha, silk, cotton, enamel or asbestos.
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