Belted cable|| Screen cable ||pressure cable|| gas filled cable|| short notes

BELATED CABLE:-

These cable are used for voltage rating upto 11 KV but in extraordinary cases Their use may be extended upto 22 KV .

° The Belted type construction is suitable only for low and medium voltage.

° the electrostatic stress developed in the cable for these voltage are more or less radial ie across the insulation.

°° for high voltage (beyond 22 KV) the tangential stresses also become important.

SCREENED CABLE :-

Used upto 33 KV but extended upto 66 KV.

It is of two type

-H type

-SL type

H TYPE :-

The insulation on each core is covered with a metallic screen which usually consists of a perforated aluminium foil.

- It has no insulating belt

- all the four screen (3 core screen and one conducting belt) and the lead sheath are at earth potential.

Advantage-

° the possibility of air pockets or voids in the dielectric is eliminated.

° the metalic screen increase the heat dissipation power of the cable.

SL TYPE :-

Constructional details is basically sm as H type cable.

- but the screen around each core insulation is covered by its own lead sheath.

- there are no overall lead sheath.

Advantage-

° The separate sheaths minimize the possibility of core to core breakdown.

° Bending of cables become easy due to the elimination of overall lead sheath

** The voltage limit for solid type cables is 66 kv .

PRESSURE CABLES :-

For voltage beyond 66 kv , solid type cables are unreliable because there is a danger of breakdown of insulation due to the presence of voids.

- Oil filled Cables

- Gas pressure cables

Oil filled Cables :-

The range being from 66 kv to upto 230 kv.

Adv -

- formation of voids and ionization are avoided

- Allowable temperature range and Dielectric strength are increased.

- If there is leakage, the defect in the lead sheath is at once indicated and the possibility of earth faults is decreased.

Dis adv -

High initial cost and complicated system of laying

Gas pressure cable :-

The cable is similar to that an ordinary solid type expect that it is of triangular shape and thickness of lead sheath is 75% that of solid cable.

- The triangular section reduce the weight

- Low thermal resistance

- The main reason for triangular shape is that the lead sheath acts as a pressure membrane .

Adv -

- cable can carry more load current.

- operate at higher voltage then normal cable

- maintenance cost is small and the nitrogen gas help in quenching any flame .

Dis adv-

- the overall cost is very high

CABLE ONLINE TEST SERIES 👉 https://quizzory.in/id/62fe3a579297986d4b3febf0

METHOD OF LAYING :-

1- Laying direct in ground

2- Laying in ducts

3- Laying on racks in air

4- Laying on racks inside a cable tunnel

5- Laying along building or structure

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