5.1 HANDLING OF CONDUCTOR AND EARTHWIRE
Handling and transporting of the conductor
and accessories shall be carried out in such a manner as to minimize the
possibility of damages from abrasion through rough handling or dirt and grit and
getting into the reel of the conductor by touching or rubbing against ground or
objects, causing injury to the conductor etc. Particular care shall be taken at
all tines to ensure that the conductor do not become kinked twisted or abraded
in any manner. If the conductor is damaged, the section affected shall be
replaced or repaired by putting joint or using repair sleeves or polishing with
emery cloth, so as to give satisfactory performance.
At all stage of construction proper care
shall be taken so that the conductor surface is smooth enough to be given
satisfactory corona and radio interference performance. All equipment used in
handling or transporting the conductor such as grips, pulleys slings, cable care
etc. shall be so designed and maintained that the surface which may contact the
conductor, are kept free of foreign or defects.
Care shall be taken while running out the
conductors such that the conductors do not touch or rub against the ground or
objects which could scratches or damage to the strands. The conductor shall not
be over strained during erection. The conductor shall be run out of the drums
from the top in order to avoid damage due to chaffing. Drum battens shall not be
removed until conductor drums are properly mounted at the drum station on the
line, and battens shall be immediately refitted on the drum if any surplus
conductor is left thereon. Drums will be transported and positioned on station
with the least possible amount of rolling, immediately after running out, the
conductor shall be raised at the supports to the level of the clamps and placed
into the running blocks. The grooves of the running blocks shall be of a design
that the seat is semi-circular and larger that the diameter of conductor/earth
wire and it does not slip over or rubs against the sides. The grooves shall be
lined with hard rubber or neoprene to avoid damage to conductor and shall be
lined with hard rubber or neoprene to avoid damage to conductor and shall be
mounted on well oiled bearings. At all stages of construction proper care shall
be taken so that the conductor surface is smooth enough to give satisfactory
corona and radio interference performance.
The running blocks shall be suspended in a
manner to suit design of the cross-arm. All running blocks specially those at
the tensioning end, will be fitted on the cross arms with jute cloth wrapped over
the steel works and under the sling to avoid damage to the slings as well as the
protective surface finish of the steel work. In case, section towers are used
even for temporary terminations, if this be unavoidable, they shall be well
guyed and steps shall be taken to avoid damage. The drums shall be provided with
a suitable breaking device to avoid damage, loose running out and kinking of the
conductor. The conductor shall be continuously observed for loose or broken
strands or any other damage. When approaching end of a drum length at least
three coils shall be left when the stringing operations are stopped. These coils
shall be removed carefully and if another and if another length is required to
be run out a joint shall be made as per the recommendations of the conductor
manufacturers. normally, the joints shall be so made that these are not required
to pass through running out of blocks, the joints will be protected with
suitable joint protector sleeves.
The conductors, joint and clamps shall be
erected in such a manner that no bird-caging over-tensioning of individual wires
or layers or other deformation or damage to the conductors shall occur. Clamps
or hauling devices shall, under erection conditions, allow no relative movement
of strands or layers of the conductors.
Repairs to conductors, in the event of
damage being caused to isolated strands of a conductor during the course of
erection, if necessary, shall be carried out during the running out operations
with repair sleeves. Repairing of conductor surface shall be done only in case
of minor damage, scuff marks etc, keeping in view both electrical and mechanical
safety requirements. The final conductor surface shall be clean, smooth and
shall be without any projections, sharp points, cuts, abrasions etc.
Repair sleeves may be used when the damage
is limited to the outermost layers of the conductor and is equivalent to the
severance of not more than one third of the strands of the outermost layer. No
repair sleeves shall be fitted within 30 m of tension or suspension clamp or
fittings, nor shall more than one repair sleeve per conductor be normally used
in any single span.
Conductor splices shall be so made that
they do not crack or get damaged in the stringing operation. Only such
equipment/methods during conductor stringing which ensure complete compliance in
this regard shall be used.
Derricks shall be used where roads,
rivers, channels, telecommunication or overhead power lines, railways, fences or
walls have to be crossed during stringing operation. it shall be seen that
normal services are not interrupted or damage caused to property. Shut down
shall be obtained when working at crossing of overhead power lines.
The proposed transmission lines may run
parallel for certain distance with the existing 400 KV, 220 KV & 132 KV lines
which will remain energised during the stringing period. As a result, there is a
possibility of dangerous voltage build up due to electromagnetic and
electrostatic coupling in the pulling cables, conductors and earthwires which
though comparatively small during normal operations can be severe during
switching and ground fault conditions on the energised lines.
The sequence of running out shall be from
to down-wards i.e. the earth wire shall be run first followed by power
After running out the top conductor the conductor at the opposite side at the
bottom level should be run out. After wards the remaining phase conductor shall
be run out. imbalance of loads or tower shall be avoidable as far as possible.
Adequate steps to prevent clashing of sub
conductors after paying out of conductor before spacers/spacer dampers are
installed. Care shall be taken that all the two sub conductors of the bundle are
taken from same conductor supplier and preferable from the same batch so
that creep behavior of these remains identical during sagging, care shall be
taken to eliminate differential sag as far as possible.
5.2 TREE CUTTING
During paying out of conductor and earthwire and
also during stringing in forest area, it shall be ensured that minimum trees are
cut and that too to the extent permitted by the forest authorities.
5.3 PULLING IN OPERATION
Before the commencement of the
stringing, initial and final stringing charts for the conductor and earth wire
showing the sags and tension for various temperatures and spans along with
equivalent spans in the lines should be available. The stringing shall be done
as per approved stringing charts.
The earth wire shall be strung and
securely clamped to the towers before the conductors are drawn up in the order
of the top conductors first, then the conductor on the opposite side and in
the end the lower conductor at the same side. it shall be ensured that all the
conductors of one section should have identical tension time history.
The pulling of the conductor into the
travellers comprising of serial and ground rollers shall be carried out in such
a manner that the conductor is not damaged or contaminated with any foreign
substance and that it may not be rubbed with the rough ground surface, or it
damages the standing crops. For this the height of ground rollers shall be
fixed in such a manner that the conductor/earthwire does by douching. The
travellers shall have size and shops most suitable for the type of stringing
and size of conductor involved and as recommended by the conductor
manufacturer. These shall be approved by the supervision Engineer before use.
The travellers surface in contact with aluminum surface of conductor shall be
of such a material that conductor is not damaged, e.g. neoprene rubber or
stainless steel. These shall be equipped with high quality ball or roller
bearings for minimum friction. They should be inspected daily for free and
easy movement in blocks during stinging and sagging.
During pulling out operation the
tension in each conductor and earthwire shall not exceed the design working
tension of the conductor at the actual prevailing temperature. After being
pulled the conductor and earthwire shall not be allowed to hang in the
stringing blocks for more than 96 hours before being pulled to the specified
sag. During the time the conductors and earthwire are on the stringing block
before sagging in, It shall be ensured that the conductors and earthwire are
not damaged due to clashing vibration or other causes.
The tensioning and sagging shall be
done in accordance with the approved stringing charts before the conductor and
earthwire are finally attached to the towers through the earthwire clamps for
the earthwire and insulator stings for the conductor. Dynamometer shall be
employed for measuring tension in the conductor and earthwire. The
dynamometers employed shall be periodically checked and calibrated with a
For 400 KV lines the following additional precautions shall be taken
The stringing of the conductor
shall be done by controlled tension method by means of tension stringing
equipments. The earthwire may also be strung by the same method. The
equipment shall be capable of maintaining a continuous tension of not less
than 10,000 kg per bundle which shall be such that the sag for each sub
conductor is maintained about 20% greater than the sags specified in the
stringing sag tables.
Controlled stringing method
suitable for simultaneous stringing of the sub conductors shall be used. All
the power conductors making one phase bundle shall be pulled in and paid out
simultaneously. The two power conductors of the bundle shall be of matched
length and of the same manufacturer and batch to ensure that the two
conductor making one phase have identical tension characteristics. After
being pulled the conductor/earthwire shall not be allowed to hang in the
stringing blocks for more than 96 hours before being pulled to the specified
Necessary arrangements should also
be made for paying out the pilot wire for stringing of conductors and
earthwire by helicopter in line route where dense forests are involved and
paying out of pilot wire by conventional method is not possible.
The complete details of the
stringing method which are proposed to be followed should be planned and
decided. Before the commencement of the stringing the stringing charts for
the conductor and earthwire showing the initial and final sags and tension
for various temperatures and spans along with equivalent spans in the lines
should be got prepared, checked and approved.
During paying out of conductor and
earthwire and also during stringing in forest area, it shall be ensured that
minimum trees are cut. If required 4 meters extension to towers may be used
to obtain proper clearance. If necessary, earthwire shall also be strung by
tension stringing equipment to avoid cutting of trees. When paying out of
conductor & earthwire by conventional method is not possible without cutting
of large number of trees, paying out may be done through helicopter as
The conductor and earth wire shall
be sagged in accordance with the approved stringing charts before they are
finally attached to the towers through the earth wire clamps for earthwire
and insulator strings for the conductors.
The conductors shall be pulled up
to desired sag and left in travellers for at least one hour after which the
sag shall be rechecked and adjusted, if necessary, before transferring the
conductors from the travellers to the suspension clamps. The conductors
shall be clamped within 36 hours of sagging in. The adjustment in sag for
creep age of conductor should also be made before finally clamping,
The sag will be checked in the
first and last span of the section in case of sections upto eight spans and
in one intermediate span also for section with more than eight spans. Any
damage to the towers or the conductors through over stressing during
stringing shall be awaited.
Dynamometers shall be used in checking the tension in the conductors and
earthwire and these instruments shall be periodically checked with a
standard dynamometer. The sags shall also be checked when the conductors
have been drawn up and transferred from aerial blocks to the insulator
The stringing blocks, when
suspended on the transmission structure for sagging, shall be so adjusted
that the conductor on the travellers will be at the same height as the
suspension clamp to which it is secured.
At sharp vertical angles the sags
and tension shall be checked on both sides of the angle. The conductor and
earthwire shall be checked on the travellers for equality of tension on both
sides. The suspension insulator assemblies will normally assume vertical
positions, when the conductor is clamped. Sagging operations shall not be
carried out under wind, extremely low temperature or other adverse weather
conditions which prevent satisfactory sagging.
5.5 CONDUCTOR DAMAGE AND REPAIR
If the conductor is damaged for
whatever reason and the damage is not repaired by repair sleeves or emery
cloth, the same shall not be used. Repairing of conductor surface shall be
done only in case of minor damages, scuff marks etc. which are safe from both
electrical and mechanical points of view. The final conductor surface shall be
clean, smooth, without any projections, sharp points, cuts or abrasions etc.
for giving satisfactory corone and R.I. performance.
All the joints on the conductor or
the earthwire shall be of compression type in accordance with the
recommendations of the manufacturers, for which the necessary tools and
equipments like, compressors and dies, grease gums presses etc, shall have to
be arranged by the contractor. These joint will be made in the best workman
like manner, shall be perfectly straight and having maximum strength. Each
part of the joints shall be cleaned by wire brush to make it free of rust or
dirt etc, and properly greased before the final compression is done with the
All joints or splices shall be made
at least 30 meters away from the structures. No joints or splices shall be made
in spans crossing over main roads, railways, small rivers or in tension spans.
Not more than one joint shall be allowed in one span. The compression type
fittings used shall be of the self centering type or care shall be taken to
mark the conductors to indicate when the fitting is centered properly. During
compression or splicing operation the conductor shall be handled in such a
manner as to prevent lateral or vertical bearing against dies. Care shall be
taken to protect the conductor from scratches, abrasions or other damages.
After pressing the joint the aluminum sleeve shall have all corners rounded,
butts and sharp edges removed and smoothened.
Clapping of the conductors in
position shall be done in accordance with the recommendations of the
manufacturer. Conductor shall be fitted with arm our rods where it is made to
pass through suspension clamps and with vibration dampers at all the
suspension and tension points, as recommended by the manufacturer.
The jumper at the section and angle
towers shall be formed to parabolic shape to ensure maximum clearance
requirements. Clearance between the conductors and ground and between jumpers
and the tower steel works shall be checked during erection and before handing
over the line. If pilot suspension string is used with jumpers, the same shall
be clamped with jumper.
Fasteners in all fittings and
accessories shall be secured in position. The security clip shall be properly
opened and sprung into position.
5.8 FIXING OF CONDUCTOR & EARTHWIRE ACCESSORIES
Vibration dampers, arm our rods and
other conductor and earth wire accessories shall be installed as per the
design requirement and as per the respective manufacturer's instructions. The
Vibration dampers, spacers and spacer dampers shall be provided at both ends
of each span at suitable distance from the supporting points for each
conductor/earthwire as per recommended practice and placement charts of
manufacturer. Spacers/Spacer damper shall be fitted within 24 hours of
conductor clamping while installing the conductor and earth wire accessories
proper care shall be taken to ensure that surface are clean and smooth and no
damage shall occur to any part of the accessories.
5.9 FINAL CHECKING, TESTING & COMMISSIONING
After completion of the works, final
checking of the line shall be done to ensure that all the foundation works,
tower erection and stringing have been done strictly according to the
specifications and approved by the supervising Engineer. All the works shall
be thoroughly inspected keeping in view the following main points -
(a) Sufficient backfilled earth is lying over each foundation pit and it is
(b) Concrete chimneys and their coping are in good finely shaped conditions.
(c) All the tower members are correctly used, strictly according to final
approved drawing and free of any defect or damage whatsoever.
(d) All bolts are properly tightened and punched.
(e) The stringing of the conductors and earthwire has been done as per the
approved sag and tension charts and desired clearances are clearly available.
(f) No damage minor or major to the conductors, earthwire accessories and
insulator strings still unattended are noticed and rectified.
After final checking the line shall
be tested for insulation in accordance with tests prescribed. All arrangements
for such testing or any other test desired shall be done. Any defect found out
as a result of such tests, shall be rectified.
In addition to the above it shall be
ensured that the total and relative sags of the conductors and earthwire are
within the specified tolerances. Such tests shall be carried out at selected
points along the route as deemed necessary.
After satisfactory tests on line, the
line shall be energised at full operating voltage.