Under ground cables ! advantage and disadvantage of ug cables ! Range of ug cables ! Type of ug cables ?

Electric power can be transmitted (or) distributed either by over-head lines system or by underground cable system. The underground cable system have several advantage, such

Advantage :-

• Less chance to damage through storms or lightning.

• Low maintenance cost.

• Less chances of fault.

• Not affected by man- made problems like sabotage,

strike etc.

• Voltage regulation in UG cables system is much better, because they have less inductive losses.

• Better general appearance of area compared to O.H

lines.

Disadvantages :-

However, their major draw back / disadvantages are

• Initial cost of UG cable system is heavy.

• • The cost of joints are more.

• Introduce insulation problems at high voltages

• compared with O.H lines.

UG cables are employed where it is

impracticable to use O.H lines like

(i) thickly populated areas, where municipal authorities prohibit O.H lines for the reason of safety.

(ii) Around plants

(iii) In Substations,

(iv) Where maintenance conditions do not permit the use of O.H construction.

Conductor :-

The conductors are made of tinned copper or aluminium and are usually stranded in order to provide flexibility to the cable and having high conductivity.

Insulation :-

-The commonly used materials for insulation are impregnated paper, varnished cambric or rubber mineral compound.

- Petrolium jelly is applied to the

layers of the cambric to prevent damage.

Metallic sheath :-

- In order to protect the cable from

moisture, gases or other damaging liquids (acids or alkalies) in the soil and atmosphere .

- a metallic sheath of lead or aluminium is provided over the insulation .

Bedding :-

- Over the metallic sheath is applied a layer of bedding which consists of a fibrous material like jute or hessian tape.

- The purpose of bedding is to protect

the metallic sheath against corrosion and from mechanical injury due to armouring.

Armouring :-

- Its purpose is to protect the cable from mechanical injury while laying it and during the course of handling.

- armouring is provided which consists of one or two layers of galvanized steel wire or steel tape.

Serving :-

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

Classification of cables :-

(i) Low-tension (L.T) cables – upto 1100 V

(ii) High-tension (H.T) cables – upto 11,000 V

(iii)Super-tension (S.T cables – from 22 KV to 33 KV

(iv) Extra high-tension (E.H.T) cables – from 33 to 66 KV

(v) Extra super voltage cables – beyond 132 KV

Cables for 3-Phase Service :-

1. Belted cables – upto 11 KV

2. Screened cables – from 22 KV to 66 KV

3. Pressure cables – beyond 66 KV

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