Tuesday, July 31, 2012

Electrical Power Cables



Power cable (a type of electrical cable) is an assembly of two or more electrical conductors held together with, and typically covered with, an overall sheath. The conductors may be of the same or different sizes, each with their own insulation and possibly a bare conductor. Larger single conductor insulated cables are also called power cables in the trade. The sheath may be of metal, plastic, ceramic, shielded, sunlight-resistant, waterproof, oil-resistant, fire-retardant, flat or round, and may also contain structural supports made of high-strength materials. 
  Cables are usually classified according to their operating voltage as follows:
1.Low voltage cables (up to 1kv).
 
2.Medium voltage cables (3kv up to 30kv).
 
3.High voltage cables (66kv up to 500kv). 
  
       
Cable Construction



The general construction of the cable is given below
1.conductor
2.Insulation
3.Assembly
4.Bedding
5.Armouring
6.sheath  
 



   
Comparison Between Copper And Aluminum
  Aluminum requires larger conductor sizes to carry the same current as copper. For equivalent capacity, aluminum cable is lighter in weight and larger in diameter than copper cable.


 
Comparison between single core and multicore cables:
      For same cross sectional area, single core cables Ampacity is greater than that of multi-core cables. But from economics point of view multicore cables are preferred.

 Insulation
 
The selection of a particular type of insulation to be used depends upon the purpose for which the cable is required and qualities of insulation to be aimed at. The following are the chief types of insulation groups that can be used:
1. Rubber
2. Polyethylene
3. Polyvinyl chloride (PVC)
4. Fibrous material
5. Silk, cotton, enamel.
6. XLPE


 Armouring
 
Steel-Tape Armouring

A steel tape is provided over the bedding but They are not very flexible, and their use is limited where bending of the cables cannot be avoided.


Wire Armouring

It has been found that a single layer of wire Armouring provides better mechanical protection as against two layers of steel tape.





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