Cables and Wires

Structure of an electric wire

BUILDING SERVICES

Wires and CablesWires and cables are purpose built conductors.

The size and type of Wire/Cable must suit the power rating required for their use. The higher the power the thicker the Wire/Cable.

WIRESDomestic and small industry wiring

In appliances

CABLESSmall and big industries

Distribution linesTransmission lines

INTRODUCTION TO WIRES

There are mainly 6 types of wires. They are:

Vulcanised indian rubber wire (V.I.R)Tough rubber sheathed wire (T.R.S)Poly vinyl chloride wire (P.V.C.)Lead alloy sheathed wireWeather proof wires Flexible wire

A VIR wire mainly consists of a tinned conductor having rubber coating.

Tinning of conductor prevents the sticking of rubber to the conductor.

Thickness of rubber mainly depends on the operating voltage to which wire is designed.

A cotton bradding is done over the rubber insulations to protect the conductor against the moisture.

Finally the wire is finished with wax for cleanliness.Nowadays these wires are not used since a better

quality wires are available at a cheaper rate.

V.I.R (Vulcanised Indian Rubber) wires.

This type of wire is a modification of V.I.R. wire. It consist of the ordinary rubber coated

conductors with an additional sheath of tough rubber.

This layer provides better protection against moisture and wear and tear. Also it provides an

extra insulation.These wires are generally available in single conductor, two conductors or three conductors.

T.R.S. (Tough Rubber Sheathed) wires.

The ordinary wires can be used only at dry places but for damp places these wires are

covered with continuous lead sheaths.The layer of lead covering is very thin like

0.12 cm thick.These wires provides little mechanical

protections to the wires.

Lead alloy sheathed wires.

These types of wires are used outdoor i.e. providing a service connection from

overhead line to building etc.In this type of wire the conductor is not tinned and the conductor is covered with three braids of fibrous yarn and saturated

with water proof compound.

Weather proof wires.

These wires consists of number of strands instead of a single conductor. (Strand is a very thin

conductor).The conductor is insulated with P.V.C. material.

These wires are very useful for household portable appliances where flexibility of wire is more

important. Typical specifications

55/.01mm(55 strands of 0.1mm diameter), maximum current 6A,used for household purposes.

Flexible wires.

A power cable is an assembly of two or more electrical conductors, usually held together with an

overall sheath. The assembly is used for transmission of electrical power. Power cables may be installed as permanent wiring within buildings, buried in the ground, run overhead, or exposed. Flexible power cables are used for portable

devices, mobile tools and machinery.

INRODUCTION TO CABLES.

GENERAL CONSTRUCTION

1. Conductor or Core.2. Insulation.3. Metallic Sheath.4. Bedding.5. Armouring.6. Serving.

TYPES OF CABLES.The types of cables

basically decided based on the

voltage level for which it is

manufactured and material used for the

insulation such as paper, cotton,

rubber etc. the classification of cables

according to the voltage levels is, Low Tension Cables (L.T.

Cables).Medium and High tension

Cables (H.T. Cables).

BELTED CABLES These cables are used for the voltage level up to 11 kV. The construction of belted cable is is shown in fig. The cores are not in circular shape. The cores are insulated from each other by use of impregnated paper. The gaps are filled with fibrous material like jute. The belt is covered with lead sheath.

SUPER TENSION (S.T.) CABLESThe S.T. cables are intended for 132 kV to 25 kV voltage levels.In such cables, the following methods are specially used to eliminate the possibility of void formation:Instead of solid type insulation, low viscosity oils under pressure is used for impregnation.Using inert gas at high pressure in b/w the lead sheath & dielectric.

OIL FILLED CABLESIn case of oil filled cables, the channels or ducts are provided within or adjacent to the cores, through which oil under pressure is circulated.It consists of concentric standard conductor but built around a hallow cylindrical steel spiral core, which acts as a channel for oil.

Cable Structure

GAS PRESSURE CABLESAn inert gas like N at high pressure is introduced lead sheath and dielectric.Gas like SF6 is also used in cables.Pressure is about 12-15 atmosphere.Working power factors is also high.

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