Conductor Stranding Perspective of Power Cable Construction
Perspective of Power Cable Construction
Conductor stranding is major standpoint of cable construction that came long experienced in different circumstances. The problem for larger sizes of solid conductors is too rigid to installation in curvy area, jointing and termination work. The solution of these difficulties becomes from conductor stranding. The procedure of stranding is used depending on the metal temper and types. In general Copper conductor and Aluminum conductors are used for power cable construction. Normally Aluminum is softer than Copper, so solid Aluminum conductor using-limit is higher than Copper.
Key Words: Concentric Stranding, Compressed Stranding, Compact Stranding, Bunch Stranding, Rope Stranding, Sector Conductors, Segmental Conductors, Annular Conductors, Unilay Conductors.
Concentric stranding is the typical choice for power cable conductors. In this construction procedure, there consists a
central wire and one or multiple layers surrounded by this central wire. The number of wires of each layer is six more wire than the previous layer; means
Numbers of wire each layer is 1, 6, 12, 18, 24, 30, 36, 42, 48, 54;
Total number of wires is 1, 7, 19, 37, 61, 91, 127, 169, 217, 271;
Number of wires across the diameter 1, 3, 5, 7, 9, 11, 13, 15, 17, 19;
In the case of power cable conductors, the core is a single wire and all of the strands have the same diameter.
The distance that takes for one strand of the conductor to make one complete revolution of the layer is called the length of lay.
As per standard specifications the outermost layer should be a left hand lay, means- as looking along the axis of the conductor, the outermost layer of strands roll towards the left as they retreat from the observer.
To get more flexible cable the number of wires should be increase in the conductor.
Compressed stranding is the slight deformation of concentric stranding which allow the wire layer being close tightly. There is no reduction of diameter is more than 3% for finished conductor of equivalent concentric stranding conductor. It reduces the gap between wires and reduces surface irregularities of the conductor.
Compact stranding conductor is similar to compressed stranding conductor, different is- it is an additional form of conductor that diameter typically 9% less than the concentric stranded conductor. As a result the diameter becomes near to a solid conductor. This type of conductor reduces air gapes; but still presents some air spaces that can causes for moisture migration.
Bunch stranding is such stranding where a collection of wires strands are twisted together. There is no geometrical arrangement for wire in conductor. This type of stranding is not used for larger size of cable, only used for smaller size where extreme flexibility is required such as extension cords.
Rope stranding is a combination of the concentric stranded and bunch stranded conductor like as “Rope”, this is a number of groups of bunched or concentric stranded conductors assembled concentrically together. Rope stranding is generally used where extreme portability is required, such as rail-road, welding cable, portable cords, etc.
Sector conductor is a typical three-conductor cable having three 120o segments that combine to form the basic circle of the completed cable. Overall diameter of the cables becomes smaller compare to equivalent rounded conductor.
Segmental conductor is round, stranded conductors collected of three or more sectors that are electrically separated from other segment by a thin layer of insulation material. Each segment carries less current than the total conductor; the current is transposed between inner and outer positions, the advantage of this cable is lower ac resistance, small skin effect. This construction is suitable for larger size of cable.
Annular conductor is round, stranded conductors whose strands are laid around a core of rope, fibrous material, or helical metal tube. Total ac resistance is less for a given cross-sectional area. This construction is used for higher size of cable.
Unilay conductor is such a construction where all of its strands used in the same direction of lay. A design frequently used for low-voltage aluminum alloy power cables.
The Power cable conductor stranding perspective of cable construction is the user demand depending on using circumstances, requirements of flexibility, capacity of power transfer, etc.