CABLE DESIGN AND CONSTRUCTION

CABLE DESIGN AND CONSTRUCTION
Major Parts of a Power Cable Design

An insulated cable appears to be a relatively simple electrical device but, in fact, it can be considered an electrical system with many components. To understand it, let us examine its components and basics of operation. For simplicity, the following discussion shall be confined to a single conductor cable. However, these fundamentals also apply to multiple-conductor cables.

The basic components of an insulated cable are the following:

1. Conductor - materials that transmits electrical energy.
2. Shielding - also referred to as screening, are used for medium to high voltage cables. Basically, the use of this stress control layers is to achieve a symmetrical dielectric fields within the cable structure. For somevoltage level, shielding may be applied over the conductor. At higher voltage levels, it is applied over the conductor and the insulation. This results in the confining of all the voltage gradients to within the cable structure if the shield over the insulation is essentially at ground potential.
3. Primary Insulation or Dielectric - prevents leakage of current from the conductor to the surroundings. It protects life and prevents damage resulting from electrical discharge. It also physically protects the conductor.
4. Jacket - also called sheath, serve several purposes such as they provide mechanical, thermal, chemical, and environmental protection to the insulated conductors they enclosed, act as electrical insulation when used over shields or armor, ease installation and routing concers by enclosing multiple insulated conductors. They may also protect the characteristics of the underlying insulation. For example,a thin nylon jacket over PVC enhances the abrasionand fluid resistance of a 600V cable. Sheathing may also include various forms  of metallic armoring, tapes, or wires to enchance the physical protection of the cable and to provide a built-in protective electricall grounded conduit for the insulated conductors. Commonly used jacketing materials include extrusions of PE, PVC, and NYLON, PVC, Nylon and PE are applied using thermoplastic extrusion lines which heat the material to the melting point andform itover thecore. The material is then cooled, usually in a water trough, and wound onto a reel. Some heat is used to soften the material so that it can be formed around the core. It is then necessary to crosslink the material to obtain its full properties.

Depending on the customer requirement and/or the application, a cable may be composed of acouple of the above-stated components or all of it. For special cases, additional sheathing or armoring may be required.