|
|
| |
|
LT
PVC Power / Control Cables.
|
| |
|
|
| |
brand, PVC insulated LT Heavy Duty cables are as per IS:1554
(Part-1) 1988 and are suitable for fixed installations. |
| |
|
CONDUCTOR : The
most acceptable metals for conductors are copper and Aluminium
due to their higher conductivity and ductility.
|
| |
|
As copper has got
higher affinity for sulphur, it corrodes in the atmosphere
where sulphur fumes are present. In these conditions tinned
copper should be used.
|
| |
|
Aluminium oxide
film which is always present on Aluminium conductor surface
acts as a barrier and it protects the Aluminium conductor
form corrosion in fumes laden atmosphere.
|
| |
|
INSULATION
: The PVC covering over Conductor is called insulation
and is provided by extrusion process only. The insulated
conductor is called core.
|
| |
|
IS: 1554 permits
two types of PVC insulation as Follows :
|
|
1) Insulation with
TYPE A PVC Compound as per IS: 5831 which is suitable for
70°C continuous operation.
|
|
2) Insulation with
TYPE C PVC compound as per IS: 5831 which is suitable for
85°C continuous operation.
|
| |
| The following colour code is used for
identification. |
| |
| Single Core |
Red
|
|
Black
|
|
Yellow
|
or
|
Blue
|
|
|
| Two Core |
Red
|
and
|
Black
|
|
|
|
|
|
|
| Three Core |
Red
|
|
Yellow
|
and
|
Blue
|
|
|
|
|
| Three & Half |
Red
|
|
Yellow
|
|
Blue
|
and
|
Black
|
|
|
| Four Core |
Red
|
|
Yellow
|
|
Blue
|
and
|
Black
|
|
|
| Five Core |
Red
|
|
Yellow
|
|
Blue
|
|
Black
|
and
|
Grey
|
| Six Core and above |
Two adjacent Cores.
Blue and Yellow ( Counting and Direction Core) and remaining
Grey in each layer. Or By printing numbers on each core.
|
|
| |
|
LAYING
UP : The cores are laid up
with suitable lay. The Final layer always has a right hand
lay i.e. if you look along the cable, the cores move to
your right hand.
|
| |
|
INNERSHEATH
: Innersheath
is provided over the laid up cores. it is provided to give
circular shape to the cable and it provides bedding for
the armouring.
|
| |
|
IS: 1554 permits
following two methods of applying the innersheath of any
thermoplastic material i.e. PVC, Polyethylene, etc.
|
| |
|
EXTRUDED
INNERSHEATH : Here
the innersheath is procided by extrusion of thermoplastic
over the laid up cores.
|
| |
|
This type of innersheath
is generally provided in cables having round cores i.e.
in control cables and in power cables up to 10 Sq.mm.size.
|
| |
|
This type of the
innersheath also acts as a water barrier between cores and
outersheath. in case of a puncture in the outersheath the
water can not reach to the cores and hence we recommend
that cables for outdoor underground uses should have extruded
innersheath.
|
| |
|
ARMOURING
: In case of armoured
cables, generally steel wire/strip armouring is provided
over the innersheath in mult-core cables and over the insulation
in single core cables. it provides mechanical protection
to inside cores and it carries earth return current in case
of a short circuit of a core with armour.
|
| |
|
As per IS: 1554
(part-1) 1988, round wire armouring is provided in cable,
where calculated diameter under armour is up to 13 mm. Above
this the armouring is either with roune wire or strip of
size 4mm. x 0.80mm. As per strip construction is economical,
the manufacturers always provide steel strip armouring unless
wire armouring is specially specified.
|
| |
|
In long run of cables
and in case of mines, round wire armouring is must, as strip
construction provides higher resistance to earth fault current
and sometimes this current may not be sufficient to operate
the circuit breaker in case of earth fault.
|
| |
|
In mines, the resistance
of the armour in on case should exceed the resistance of
the main core by more than 33% for safety reasons. To achieve
this, some times tinned hard drawn copper wires are required
to be used along with galvanized steel wires. Sometimes
two layers of steel wires are provided to give extra protection.
|
| |
|
In case of single
core armoured cables for use in ac circuits, the material
for armouring has to be non magnetic, as in this case the
return current is not passing through the same cable and
hence it will not cancel the magnetic lines produced by
he current. these magnetic lines which are oscillating in
case of AC current will give rise to eddy current in magnetic
armouring and hence armouring will become hot, and this
may lead to the failure of the cable. generally hard drawn
aluminium wires/strip are used for armouring in this case.
|
| |
|
OUTERSHEAT
: The PVC convering on armouring in case
of armoured cables and over the innersheath in caseof unarmoured
cables is called outersheath.
|
| |
|
IS: 1554 specifies
nominal and minimum thickness of outer sheath for unarmoured
cables and only minimum thickness of outer sheath for armoured
cables.
|
| |
| it permits the following types of outer
sheath PVC Compounds. |
| |
|
1) Outer sheath
with Type ST1PVC Compound as per IS:5831, which is suitable
for 70° C Continuous opration.
|
|
2) Outer sheath
with Type ST2PVC Compound as per IS:5831, which is suitable
for 85° C Continuous opration.
|
| |
|
In the modern power,
Chemical, Fertiliser and Cement Plants many PVC cables are
bunched in the cable shaft or on cable trays. in case of
fire in these cables, the fire becomes self sustaining.
moreover due to the burning of PVC a dense corrosive smoke
is emitted which makes fire fighting very diffcult, due
to poor visibility and toxic nature of the smoke. HCL content
of the smoke, not only damages other costly equipment lying
nearby, but also penetrates the RCC and corrodes the steel
reinforcement. Due to this there is an extensive damage
of the property.
|
| |
| To remove these deficienciencies FRLS
i.e. Fire Retardant Low Smoke PVC was developed. |
| |
|
If required, we
can provide Fire Retardant Low Smoke (FRLS) PVC inner sheath
and /or outer sheath. this PVC compound, apart from meeting
the requirments of type ST2 as per IS: 5831, has got better
fire retardant properties and it emits lower smoke and acid
fumes when it catches fire.
|
| |
TESTS
: Testing is a very important part of cable manufacture
and all raw materials and finished cables must be thoroughly
tested to ensure the quality of cables.
has a well equipped test fields and electrical, mechanical
and chemical laboratories capable of carrying out all tests,
which are required as per relevant specifications. The most
modern testing equipment is installed in these laboratories.
|
| |
| The following tests are carried out
on each and every length of cables before it leaves the factory. |
| |
|
(A)
Conductor Resistance Test : The tests ensure
that conductor resistance is within the specified limit,
thereby verifying that the continuity of conductor is maintained
throughout the cable length and that the conductor has the
required electrical section DC. resistance is measured at
room temperature and is then corrected to standard reference
temperature of 20°C.
|
| |
|
(B)
High Voltage Test : This test ensures that
insulation will safely withstand the rated voltage with
permissible variation in normal operation.
|
| |
| CABLE
CODE : The following codes are used for designating
the cables as per IS: 1554. |
| |
|
CONSTITUENT
|
CODE
LETTER
|
| COPPER
CONDUCTOR |
--
|
| ALUMINIUM
CONDUCTOR |
A
|
| PVC
INSULATION |
Y
|
| STEEL
ROUNDWIRE ARMOUR |
W
|
| STEEL
STRIP ARMOUR |
F
|
| STEEL
DOUBLE ROUND WIRE AROMOUR |
WW
|
| STEEL
DOUBLE STRIP ARMOUR |
FF
|
| PVC
OUTER SHEATH |
Y
|
| COPPER
CONDUCTOR, ROUND WIRE ARMOURED AND PVC SHEATHED CABLE
|
YWY
|
| ALUMINIUM
CONDUCTOR, STEEL STRIP ARMOURED AND PVC SHEATHED CABLE
|
AYFY
|
|
| |
|
The weights of
the cables mentioned in the following tables are approximate
and given for guidance only. They should never be used as
criteria to check the lengths of the cables supplied. The
best way to check the length of thesupplied cable is by
resistance only. Take the resistance of the full drum and
divide the reading by the resistance of 1 mtr. length. To
decide the size of the conductor, particularly that of the
sector shaped conductor, we recommend the following method
Take weight of a small conductor piece and measure its weight
in grams. Then find out the weight of the conductor in gms
per metre length. Divide it by 2.7 in case of Aluminium
and by 8.9 in case of Copper. It will give the area of the
conductor in sq. mm.
|
| |
|
|
| |
