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The following are some of the
salient factors which should be kept in view during
installation of PVC Insulated Heavy Duty Cables:
1. Before laying, the insulation of the cable should be
checked with megger as preliminary check against any probable damage.
2. The drum should be always rolled in the "direction of
arrow for rolling", marked on the drum. In the absence of any
such mark, the drum should be rolled in the direction same as that
of inside end of the cable and opposite to that of the outside end.
3. Where the cable is to be jointed with existing cable, the
sequence of cores at the two ends to. be jointed should be in
the opposite direction, i.e. if at one end it is in clockwise
direction, at the other end it should be in anticlockwise
direction. This is necessary to avoid the crossing of cores
while jointing. This will also decide the direction in which the
cable is to be pulled.
4. Wherever possible bending radius of 12 times the overall
diameter of the cable should be maintained, but in any case it should
not be less than 8 times.
5. Where the cables are necessarily laid and jointed in
very cold regions, both the cable and the ambient temperatures should be
above O° C and have remained so for the previous 24 hours. During such
conditions, the cable should also not be bent to very small radius. This
is due to the reason that at very low temperatures PVC compounds become
stiff and brittle, and are likely to crack and shatter when stuck hard
or bent to small radius.
6. A joint being the weakest point of the electric power
transmission system, all necessary precautions should be taken. Jointing
materials and accessories like conductor ferrules, solder, insulating
and protective tapes, protective filling compound, joint boxes, etc. of
right quality and sizes should be procured. The application of these
materials should be made skillfully for the jointing work. In this
connection, it is always advisable that the method and the working
instructions of the supplier should be strictly followed.
7. Armoured Cables: All bonding clamps at the
joints and terminations and the armour wires should be thoroughly
cleaned. The clamps should be adequately tightened. This is
necessary to ensure proper electrical contact, because
armour is the only return path for earth fault current.
Unarmoured Cables: In case of unarmoured cables, the
external metallic earth bonding connector of adequate size should be
used.
8. Earth : All joints, terminations, armour wires
and external metallic bonding should be connected to earth. Wherever
possible, armour at one end of the cable should be connected to main
earth system at the supplying end by employing metallic connectors.
Precautions should be taken to eliminate the chemical and bimetallic
corrosion of the earth connector or bonds.
9. Filling Compound :
a. The design of the box and the composition of the filling compound
should provide an effective provide an
effective sealing against entry of moisture to conductor
ferrules and armour connectors.
b. If hot pouring protective compounds are used, the
temperature of the compound while pouring should not
exceed 150º C
10. Test after installation :
After the cable is installed a.d.c. voltage test may be carried out. Each
core should be tested at 4 kv against others and the armour, the latter
connected to earth.
The voltage should be increased gradually to full value and
maintained continuously for 15 minutes. no breakdown of insulation
should occur during test.
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Installation Of PVC Insulated Heavy Duty Cables