PRACTICAL
NO:-7
AIM: IDENTIFY AND SPECIFY DIFFERENT
TYPES OF WIRES, CABLES, CABLE JOINTS USED FOR DIFFERENT CURRENT AND VOLTAGE
RATINGS.
THEORY:
Wires are used for passage of electric current in many ways from generating power plant to various distribution levels like (1) In overhead Transmission and distribution lines,(2) In giving service connection to various consumers,(3) In winding coils of electrical machines,(4) In house and industrial wiring,(5) In underground cables etc.For conduction of small current, single standard insulated copper conductors are used. As per the current rating, the conductors have specific diameter or cross-sectional area and level of insulation depends upon voltage rating. Following various types of wires and cables are used in domestic and industrial wiring:
1) V.I.R.( Vulcanized India Rubber) wire.
2) C.T.S. or T.R.S. (Cab Tyre Sheathed or Tough Rubber Sheathed) wire.
3) Weather proof wire.
4) L.C.(Lead Covered) wire.
5) MICC (Mineral insulated copper covered) wire.
6) PVC (Poly Vinyl Chloride) wire.
7) Flexible
wire.
1)
VIR (Vulcanized India rubber) wire:
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| Figure 1 Single Braided VIR Wire |
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| FIGURE 2 Double Braided VIR Wire |
In this type of wires conductors are made up
of aluminum or copper. A layer of vulcanized rubber is provided over it. There
may one or two layers. Over this a cotton tape is wound and braiding of
impregnated cotton is wound over it.
Single braided wire and
double braided wire is shown in figure. These types of wires can bear little
mechanical stress. Due to the effect of water, moisture etc. its insulation
properties are reduced. Chemicals also effect the insulation and it may be cut
due to the sharp tools etc. Due to excessive heat the rubber may melt.
2)
CTS or TRS (Cab tire Sheath or tough rubber sheath) wire:
In this type of wire layer of strong and
durable rubber is provided over the conductor. Its mechanical strength is more
than that of the VIR wire. Effect of heat, moisture and water is less in it.
This type of wire is available in varieties of single core, twin cores and
three cores. It is used in house wiring and industrial wiring. Single core and
twin core wire is shown in figure.
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| FIGURE 3 Single Core TRS Wire |
FIGURE 4 Twin Core TRS Wire
(3) Weather proof wire:
On this type of wire there is no effect of
atmosphere. A layer of rubber is provided on copper conductor. Braiding of
cotton is provided on this. It is made waterproof by dipping it into waterproof
compound. This type of wire is available in single core or double core types.
Outer sheath is inflammable so it is ot used in casing-capping type wiring and
the places where there are inflammable materials. It is useful in service
connections. Its use is nowadays has become limited.
(4)
LC (Lead Covered) wire:
In this type of wire coating of insulated
rubber is provided on the conductor. A tube made of lead is kept over it. Due
to there is no effect of moisture on the rubber. So it is used in the place
where there is presence of moisture. As Lead is soft. It is easily affected by
mechanical stresses. So care has to be taken while using it. This wire can be
used directly on wooden batten.
(5)
MICC (Mineral insulated copper covered) wire:
In this type of wire coating of magnesium
oxide is provided as insulation on the copper conductor. Over this copper
sheath is provided. When this wire has to be used in moist atmosphere, a
serving made of PVC is provided over this. This wire is less affected by
temperature. This type of wire is used in wiring in mines, factories,
refineries, furnace, boilers, rolling mills etc.
FIGURE 5 MICC Wire
(6)PVC
(Poly Vinyl Chloride) Wire:
In this type of wire insulation made of poly
vinyl chloride is provided over copper or aluminum conductor. PVC wires are
widely used and use of paper and rubber insulated wires is reduced. This type
of wire is manufactured for voltage rating of 11 KV. It is available in single
PVC and double PVC Types. This type of wire is also available in twin core and
three core circular and two core flat types.
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| FIGURE 6 Single PVC Wire |
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| FIGURE 7 Double PVC Wire |
(7)Flexible
wire:
FIGURE 8 Flexible Wire
In
this type of wire instead of using thick conductor many thin copper conductors
of 36 gauges are used. This is called stranding. These wires are available in
the size of 14/36, 23/36, 40/36 etc. These strands are twisted and PVC
insulation is provided over it.
Such
two wires of different colors of insulation are twisted together and coil is
prepared. As the flexible wire is used instead of thick wire, the wire can be
bent in any direction. This type of wire is used in giving connections to table
lamp, fan, tube light etc.
CABLES:
Cables are classified according to basis of construction.
(1)Low tension cable
(2) Belted cable
(3) Screened or H type
cable
(4) SL type cable
(5) HSL type cable
(6)Super tension Cable
(1)
Low Tension cable:
Vulcanized India rubber (VIR) cables are
manufactured for the voltage ratings of 250/440V and 650/1100V. Aluminium or
copper core is used. Insulation of VIR is provided on the core. Braiding of
cotton, tough rubber sheath or metal sheath is used.
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| Figure 9 Construction of Single Core PVC Cable |
Figure 10 screened or H type cable
PVC cables are becoming popular. In this,
there is insulation of PVC over the copper or aluminium core. Sheath of PVC is
provided over the insulation. There is armoring of steel tape or steel wire
over the sheath. There is covering of PVC over the armoring which works as the
serving.
(2)
Screened or H type Cable:
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Figure 10 screened or H type cable
|
This
type of cable was developed by M Hochstadter so this type of cable is known as
the H type Cable. Figure shows the telescopic view of this type of cable. Each
core is insulated and then a screen of metalized paper is wound round it. So
this type of cable is called the screened type cable. Metalized screen is
perforated so the process of impregnation can be done easily.
(3)
Belted cables:
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| Figure 11 Belted Cables |
Belted cables are used for the medium voltages.
Construction is similar to the LT Cables. There is paper insulation surrounding
the core, which is called the belt. Figure (a) shows two-core shaped cable.
Figure (b) shows three core shaped cable. Figure (c) shows the round core
three-core cable while figure (d) shows four-core shaped cable.
(4) SL cable:
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| Figure 12 SL Cable |
SL cable means separate lead sheathed cable.
In this Type of cable, there is paper insulation surrounding the core. There is
Separate lead sheath over each core. So all the three cores work as separate
cable and the dielectric stress become radial. No overall lead sheath is used
surrounding the three cores. Bedding, armoring and serving are provided like
other cables.
(5)
HSL Cable:
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Figure 13 HSL Cable
|
This
type of cable is the combination of H type and SL type cables. Paper insulation
is provided over each core. Metalized paper is wound over the insulation and
lead sheath is provided over this. Filler space is filled with copper woven
fiber material. Bedding, armoring and serving are provided as usual.
(6)
Super Tension Cable:
In this type of cable no additional arrangement is
made to prevent the formation of voids. If the cables are to be used for 132 KV
and 220 KV, arrangement has to be made to prevent formation of voids and to
increase the dielectric strength. This can be achieved by two ways.
(1)By
using the oil filled cables
(2)
By using the gas filled cables.
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| Figure 14 Single Core Cable with Oil Channel in Conductor |
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Figure 15 single core oil filled cable with oil channel in the sheath
|
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Figure 16 Three Core Cable with Oil Channel in the Filler Space
|
CONCLUSION:
