General Construction of Cable

 General Construction of Cable

The general construction of a 3-Conductor cable. It mainly consists of various parts, namely

1.      Core (or) Conductor

2.      Insulation

3.      Metallic Sheath

4.      Bedding

5.      Armouring

6.      Serving

1. Core (or) Conductors: A cable may cosist of one (or) more than one Core depending upon the type of service and it’s Use. The Conductors are made of tinned copper (or) aluminium and are usually stranded for obtaining the flexibility in the cables.

2. Insulation: In cables, generally each core is provided with a suitable thickness of insulation and it is mainly depends on the operating voltage.

The commonly used insulating materials  are impregnated paper, varnished cambric (or) rubber mineral compound.

3. Metallic Sheath: In order to protect the cable from moisture, acids (or) alkalies and gass in the soil and atmosphere, a metallic sheath of lead (or) aluminium is provided over the insulation.

4. Bedding: A layer of bedding is placed over the metallic sheath of a cable for the purpose of protecting the metallic sheath from corrosion.

5. Armouring: Over the bedding, Armouring is provided which consists of one (or) two layer of Galvanised steel wire (or) steel tape.

Its main purpose is to protect the cable from mechanical injuries.

7. Serving: In order to protect armouring from atmospheric conditions, a layer of fibrous material (like jute) is provided over the armouring is known as serving.

Classification of Cables

The cables are mainly classified in to different types according to

1. Number of Conductors

(a)   Single Core

(b)   Two core three core

(c)    Three core

(d)   Four core

2    2. Rating of Voltage

(a)   Low Voltage (L.W) Cables for operating voltage up to 1000 volt.

(b)   High Voltage (H.T) Cables for operating voltage up to 11,000 volt.

(c)    Super Tension (S.T) cables for operating voltage up to 33,000 volt.

(d)   Extra High Tension (E.H.T) cables for operating voltage up to 66,000 volt.

(e)   Extra Super Voltage (E.S.V) cables for operating voltages of 132KV above.

3.     Nature of application of Insulation and Lead sheathing

(a)   Belted Cable

(b)   H- Type

(c)    S.L Type

(d)   HSL Type

4.     Method of Improving the dielectric Stress

(a)   Solid Type

(b)   Oil Filled Type

(c)    External Oil Pressure Type

(d)   Gas Pressure Type