CABLE INSULATION IN POWER CABLE TECHNOLOGY

Cable Insulation In Power Cable Technology - Cable is a medium to deliver electrical energy. in an electrical wiring generally consists of an insulator and a conductor. Isolator is a cable wrapping material is generally made of plastic, while the conductor is made of copper or aluminum.

Cable Insulation In Power Cable Technology

Cables are usually classified according to the type of insulation used. the type of insulation to be used must have the following properties:

• it should have specific resistance.
• it should have high dielectric strength
• it should be tough and flexible.
• it should not be hygro:copic i.e. it should not absord moisture from air or surroundings.
• it should be capable of standing high temperatures without much deterioration.
• it should be non-inflamable.
• it should not be attacked by acids or alkalies.
• it should be capable of withstanding high rupturing voltage.

Althought it is not possible to have all the above mentioned qualities in one particular type of insulation. the selectionof a particular type of insulation to be used is dependent upon the purpose for wich the cable is required and qualities of the insulation to be aimed at. the following are the chief types of insulation groups wich can be used:

• Rubber.
• Polyethylene.
• polvinyl chloride (P.V.C)
• Fibrous material such as paper or jute.
• Vulcanized bitumen.
• Gutta-percha.
• Silk, Cotton, enamel.

Rubber 

Rubber is the most commonly used insulation in cables. Rubber has a dielectric constant between 2 and 3, dielectric stress is 350 kV/cm. approximately, and spesific resistance of 10^17 Ohm/cm. It absorbs moisture slightly and the maximum safe temperature is approx. 38 C. So, pure rubber cannot be used as an insulation since it cannot withstand high temperatures and cannot be put to rough usage, being too soft. Thus, mostly the rubber used as an insulation on wires consists of 20 to 40 per cent of India rubber, the remainder being mineral matter such as zinc oxide, red lead etc. also a little bit of sulphur is added. the method of applying insulation is given below.

Polythylene

It is thermoplatic synthetic resin and has very good dielectric and ageing properties. it is a tough and flexible material having exelent electrical and mechanical properties as an insulating material. It has a dielectric strength of 400 kV per cm. Polyethelene is non-imflamable material. Even if a flame is continously applied to the polyethylene. the buraing will stop after a burning will stop after a few oms. away  from the flame. due to threre proporties it is being extensively used as an insulation.

Polyvinyl-Chloride

It is a thermo-plastic synthetic resin and is being widely used as an insulation. it has high electrical resistivity, good dielectric strenght and mechanical toughness over a wide range of temperture. moistures acids and alkalies do not affect P.V.C. insulated cables are usually employed for medium and low voltage domestic industrial lights and power instalations.

Paper
 paper insulation in power cable has almost superseded the rubber insulation. the foremost reason of this is that it is quite cheap and has low capacitance and high dielectric strength.

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