STRANDING OF WIRES AND CABLES

STRANDING OF WIRES AND CABLES
Various Ways of Stranding a Power Cable/Wire

The conductor material may be either solid or stranded. A solid conductor is a single, solid strand of conductor for the whole length of the wire, while stranded conductor is composed of several strands of conductor concentrically wounded together over the whole length of the wire/cable. For the same cross-sectional area of a conductor, there are diameter differences between solid and various types of stranded conductors. This is an important consideration in the selection of connectors and in the methods of splicing and terminating.

Largesizes ofsoild conductors are too rigid for many applications that the solution would be to aveasmaller wiresandstrand them together to form the conductor. There are several ways of stranding the wires together which is dependent of the type and temper of the metal used. The following subsections will discussthe most commonly used stranding for copper conductors.

• Concentric Stranding: This consists of a central wire or core surroundedby one or more layer of hellically applied wires. Each layer is aplied in a direction opposite to the layer underneath, except for unilay construction wherein the layers are applied in the same lay direction.

• Compressed Stranding: This construction slightly deforms thelayers to allow the layer being applied to close tightly. The diameter of the conductor can be reduced by up to 3% of the equivalent concentric strand.There is no, however, reduction in the conductor area.

• Compact Stranding: This is similar to compressed stranding except that additional forming is done to reduce the conductor diameter typically by 9 % less than its equivalent concentric stranded conductor. The resulting diameter is a near solid conductor.

• Bunch Stranding: In this construction the conductor strands are twisted together in the same direction without any regard to the geometric arrangement. Commonly used when very flexible wire is required for small conductor sizes, such as portable cables.

• Rope Stranding: This is a combination of the concentric conductor and a bunch stranded conductor. The complete conductor is composed of a number of groups of bunched or concentric stranded conductors assembled concentrically together.

• Sector Conductors: The cross-section of these conductors is approximately the shape of a circle's sector. A multi-conductor insulated cable with three sector conductor cables have three 120 degrees segments that combine to form a circle as a finished cable. This cable have smaller diameter than the cable with round conductors. Also, these cables have lower ac resistence due to a reduction of the proximity effect.

• Segment Conductors: Asegmental conductor is a round,stranded conductor composed of three or four sectors slightly insulated from one another.This construction has the advantage of lower a-c resistance due to less skin effect.

• Annular Conductors:The round stranded conductors are laid around a suitable core. The core is usually made wholly or mostly of non-conducting material. This construction has the advantage of lower total a-c resistance for a given cross-sectional area of conducting material by eliminating the greater skin effect at the center.