Electrical Stranded Conductors

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Key learnings:

Stranded Conductors Definition: A stranded conductor consists of several thin wires called strands, making it flexible and suitable for electrical power systems.
Transmission and Distribution: Stranded conductors are crucial for transmitting and distributing electricity over long distances.
Construction: Typically, these conductors have a steel core for strength and aluminum strands for conductivity.
Stranding Process: Strands are twisted together in layers, with each layer twisted in opposite directions for added flexibility.
Flexibility: The flexibility of stranded conductors increases with the number of strands, making them easy to transport.

Stranded conductors combine several smaller wires into one conductor. They are used throughout electrical power systems, including overhead lines, cables and flexible connections.

The figure shows aluminium conductor steel reinforced, or ACSR. In this specific design, aluminium strands carry most of the current while a steel core adds mechanical strength to the conductor. A steel core is not a feature of every stranded conductor; other designs use strands made entirely from copper, aluminium or another conductor material.

The main practical benefit is flexibility. A large solid wire is stiff and can be damaged by repeated or tight bending. Dividing the same conductor area among smaller wires makes a stranded conductor easier to bend, coil, pull and install. The exact flexibility depends on the strand count, wire diameter and stranding class.

Facts about Stranded Conductor

The following points describe conventional concentric-lay stranded conductors made from equal-diameter round wires:

A stranded conductor can be coiled and handled more easily than a solid conductor of similar size.
For the same total conductor area, using more, finer strands generally increases flexibility. The applicable stranding class determines the actual construction.
A concentric-lay conductor has a central wire or core surrounded by complete layers of strands.
The strands in each layer follow a helical path over the preceding layer. Manufacturing this arrangement is called stranding.
In conventional concentric lay, successive layers usually use opposite lay directions. This helps keep the finished conductor mechanically stable. Unidirectional and unilay constructions also exist, so opposite lay is not universal. In the formulas below, x is the layer count with the centre wire counted as layer 1.
For complete concentric layers of equal-diameter strands, the total number of wires in the conductor is:

Here, N is the total number of strands and x is the layer count. The sequence is 1, 7, 19, 37 and 61.
For the same ideal equal-diameter construction, the nominal conductor diameter is:

Here, D is the overall conductor diameter,
and d is the diameter of one strand.