Conductor Stranding Perspective of Power Cable Construction

Conductor Stranding Perspective of Power Cable Construction

Conductor stranding is a major aspect of cable construction that came long experience in different circumstances. 

The problem with larger sizes of solid conductors is too rigid for installation in curvy areas, jointing, and termination work. The solution to these difficulties comes from conductor stranding. 

The procedure of stranding is used depending on the metal temper and types. In general Copper conductor and Aluminum, copper conductors and aluminum conductors are used for power cable construction. Normally Aluminum is softer than Copper, so the use limit is higher than that of copper.

Fig: Conductor strands arrangement system

Key Words: Concentric Stranding, Compressed Stranding, Compact Stranding, Bunch Stranding, Rope Stranding, Sector Conductors, Segmental Conductors, Annular Conductors, Unilay Conductors.

Concentric Stranding:

Concentric stranding is the typical choice for power cable conductors. 

In this construction procedure, there is a 

central wire and one or multiple layers surrounded by this central wire. 

The number of wires of each layer is six more wires 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 it 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, which 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 a more flexible cable, the number of wires should be increased in the conductor.

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Compressed Stranding:

Compressed stranding is the slight deformation of concentric stranding that allows the wiring layers to be closer together. 

There is no reduction in diameter of more than 3% for the finished conductor of equivalent concentric stranding conductor. 

It reduces the gap between wires and reduces surface irregularities of the conductor.

Compact Stranding:

A compact stranding conductor is similar to a compressed stranding conductor; the difference is that it is an additional form of conductor with a diameter that is typically 9% less than the concentrically stranded conductor. 

As a result, the diameter becomes close to that of a solid conductor. This type of conductor reduces air gaps, but still presents some air spaces that can cause moisture migration.

Bunch Stranding:

Bunch stranding is such stranding where a collection of wire strands is twisted together. There is no geometrical arrangement for the wire in the conductor. 

This type of stranding is not used for the larger size of the cable, but only for a smaller size where extreme flexibility is required, such as extension cords.

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Rope Stranding:

Rope stranding is a combination of concentric stranded and bunch stranded conductor like as “Rope”; this is several groups of bunched or concentric stranded conductors assembled concentrically together. 

Rope stranding is generally used where extreme portability is required, such as for railroad, welding cable, portable cords, etc.

Sector Conductors:

A sector conductor is a typical three-conductor cable having three 120 ° segments that combine to form the basic circle of the completed cable. 

The overall diameter of the cables becomes smaller compared to the equivalent grounded conductor.

Segmental Conductors:

The segmental conductor is a round, stranded conductor composed of three or more sectors that are electrically separated from one another 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 the larger size of cable.

Annular Conductors:

The annular conductor is a round, stranded conductor 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 the larger size of cable.

Unilay Conductors:

Unilay conductor is such a construction where all of its strands are used in the same direction of lay. A design frequently used for low-voltage aluminium alloy power cables.

The Power cable conductor stranding perspective of cable construction is the user demand, depending on the circumstances, requirements of flexibility, the capacity of power transfer, etc.