Section VI.
Requirements Page VI-56
− Rust removal using abrasive paper or metal brush from zones where corrosion and non-
adhering films of zinc are apparent. Cleaning with a solvent and wiping dry. Treatment process-
es using phosphoric acid will be prohibited.
− Application of one or two layers of the previously mentioned paint (minimum dry coat thickness:
100 microns) to be applied according to the supplier's instructions.
Holes drilled on site (subject to the approval of the Employer) will be painted as indicated above be-
fore assembling the components.
Erection of insulator sets and accessories
This operation will include, as a minimum:
− Sorting of parts,
− Checking the consistency of the parts with the planned assemblies,
− Transport to erection sites,
− Assembly,
− Cleaning and fitting to the towers.
The support equipment will be assembled in accordance with the supplier's assembly drawings duly
approved by the Employer. No defective equipment will be used. No insulator will be fitted in the sets if
its surface has the slightest chip. All the insulators shall be free from all traces of mud or other solid
impurity at the time of erection.
The galvanized support equipment will be handled and erected so as to maintain a perfect surface
state and to avoid any deformation of the parts. The bolts will be tightened using a torque wrench ac-
cording to the manufacturer's instructions.
Tension sets pulling upwards will be assembled with the insulators reversed with respect to the normal
arrangement.
The pulleys designed to pull the cables will be installed at this moment.
2.4.7 Pulling and sagging of cables
The pulling and sagging method will be subject to the Employer's approval. The procedure report will
detail
− Special precautions for the sections parallel to railroad and existing transmission lines (induction
risk)
− Stringing conductor and earthwire
− Stringing OPGW
− Precaution for OPGW
− Tools and equipement
− Repair of damaged conductors and OPGW
− Earthing of conductors, OPGW and stringing equipment
− Jointing of conductors and OPGW
− Clipping in
− Transport of the cable drums, accessories and tools to the pulling sites.
− Installation of protection templates on the railway line, road and other crossings.
− Stringing under mechanical tension, pulling and sagging the cables.
− Manufacture of joints, tension clamps and jumper loops.
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Transmission lines component
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Section VI. Requirements Page VI-57
− Fitting of downleads on the transformer station gantries. Connection of the HV equipment to the
conductors shall be the scope of the substation contractor.
− Installation of miscellaneous accessories (armour rods, vibration dampers, marker balls, spac-
ers, etc.).
− Return of surplus equipment, site cleaning and reinstatement.
Cable pulling
Cable drums will be suitably protected during storage, handling and transporting operations so that,
when the cables are pulled, neither the drums nor the cable will show any traces of damage.
It is expressly specified that the cables will be held permanently above ground, metal surfaces and
other obstacles by means of intermediate supports of adequate height, suitably placed and in suffi-
cient numbers. The installation of protection gantries for passing over dwellings, lines of communica-
tion, HV, MV or LV power lines and other obstacles will be an integral part of the works. The arrange-
ments to be made during the works (clearance height, monitoring, notification, etc.) will be taken at the
Contractor's expense to the satisfaction of the administrative authorities or private individuals con-
cerned, with whom the Contractor will be required to make prior contact.
The cables will be strung and pulled under mechanical tension using a winch and a tensioner, thereby
enabling the cable to be kept under tension and preventing the conductor from dragging along the
ground thus removing any risk of damage on sharp edges. At the proper time, the Contractor shall
submit to the Employer for approval a detailed note describing the stringing and pulling method and
the tools that he plans to use.
At the supports, the cables will rest on ball-bearing pulleys of an approved model so as to avoid any
damage to the cable. Their effective diameter will be at least 20 times the cable diameter for the phase
conductor and for the Earthwire. As an alternative, if a series of smaller pulleys is used, they must be
arranged so that the cable rests on a radius equivalent to at least 20 times the conductor diameter.
The pulley hooks shall be of uniform length so that the conductors will be maintained at a uniform dis-
tance, not exceeding 500 mm above or below their final position once they have been attached.
The tension in the cables at the drum outlet must not exceed the value indicated by the cable supplier.
It shall always be possible to monitor this value by a permanent indicator on the tensioner.
Except in cases where they are crimped on to sacrificial cable ends, the come-along clamps will be of
the parallel jaws type with smooth contact surfaces, without undulation; they will be of sufficient length
to ensure that the cable can be tensioned without folding, notching or sliding the cable strands and
without any relative slippage with respect to the grease-impregnated steel core.
The cables will not be lifted by means of tools with a small radius of curvature or which may damage
the cables; the curvature of the contact surface will be at least equal to that specified above for the
pulleys.
Any portion of cable that shows traces of damage of any kind will be eliminated. Rejected cable
lengths that are less than 150 m long will not be used for the main line. However, they may be used to
make jumper loops.
During the pulling and sagging operations, the cables will be adequately earthed to guard against any
accident due to lightning strikes.
Making joints and tension clamps
The joints and the compression type tension clamps will be made according to the supplier's instruc-
tions and to ensure a guaranteed electrical conductivity, on one hand, and on the other hand a me-
Bidding documents – REGIONAL RUSUMO FALLS HYDROPOWER PROJECT
Transmission lines component
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Section VI. Requirements Page VI-58
chanical strength of tensioned parts at least equal to 95% of the theoretical failure load of the cables
on which they are installed.
The ends of the cables will be perfectly cleaned before inserting them in the joints or clamps and, in
particular, will be free from grease. The sleeves to be compressed shall be filled with a special paste
according to the supplier's instructions.
After compression, the tension clamps and the joints shall be as straight as possible. The joints and
tension clamps will be subject to the Employer's approval; any poorly made joint will be remade by the
Contractor at his expense.
The junction surfaces between the tension clamp body bracket and the collar shall be clean and flat.
For this purpose, the two contact surfaces will be brushed in order to eliminate the alumina layer and
coated with an appropriate contact grease or paste recommended by the manufacturer of the cou-
plings.
Except for the ends of the cables on the drums, the use of joints will be avoided. There will be no more
than one joint per cable and for five spans, nor any joint at a distance of less than 50 m from dead-end
joints. There will be no joints in sections crossing roads, railway lines, lakes, rivers, etc.
In the event of damage to the cable, the Contractor will submit a repair method to the Employer: nor-
mal joint or repair joint, or cutting of certain cable lengths.
Cable Sagging
Sagging will be carried out separately for each laying section, delineated by the supports equipped
with tension insulator assemblies. Intermediate sagging will be undertaken whenever the horizontal
component of the tension cannot be guaranteed because of friction in the pulleys and the high number
of spans or differences in levels.
Contractor shall submit to the Employer for approval a fully detailed stringing schedule stating the fol-
lowing indications:
− The locations of conductor and earth wire drums and pullers
− The proposed position of mid-span joints,
− The maximum tensions to be used during running out of pilot wires, conductor, earthwire and
OPGW,
− The sag of each span and the stringing chart
− The crossing of roads, rivers
− The crossing and proximity of overhead lines (with their definitive outage requests) or railroad
− Protection of important crossings
The pulling under mechanical tension and sagging operations will be carried out in such a manner that
the towers will never be overloaded. To this end, the Contractor will gather all necessary information,
in particular the tables of maximum permissible forces for the supports and the load cases to be con-
sidered. The Contractor may have to fit guy lines to certain supports or crossarms that were not
planned for the load cases encountered during erection. This type of operation shall be limited to the
strict minimum necessary.
In addition, the tension applied to the cables shall not exceed the maximum tension indicated in the
cable laying tables given the fact that the cable is subject to such phenomena as creep under the ef-
fect of stresses acting on it after it has been installed.
During each sagging operation, the conductors will be treated as uniformly as possible, so that they
are subsequently subject to the same degree of creep. To this end, every effort must be made to
Bidding documents – REGIONAL RUSUMO FALLS HYDROPOWER PROJECT
Transmission lines component
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Section VI. Requirements Page VI-59
complete a sagging operation in the same day and for all the conductors in a given section, wherever
possible.
The conductors and OPGW shall be sagged in accordance with tension/sag tables calculated by the
Contractor and approved by the Employer.
Compensation for the inelastic extensions shall be made by the selection and use of an over tension-
ing the conductor at the time of erection. Over tensioning of the conductor shall be made by an allow-
ance in the erection temperature i.e. Sagging temperature equals conductor temperature minus
equivalent temperature correction. The Contractor shall submit stringing sag and tensions chart which
shall be follows:
− -15 °C correction than the design sag and tension chart for aluminium cables
− -10° C correction than the design sag and tension chart for aluminium steel cables
The Contractor shall use approved dynamometers, accurate sighting and/or other apparatus neces-
sary for the proper checking of the work. Every shall be offered to the Employer for inspection of the
results before sagging equipment, dynamometers, sighting or other apparatus is removed from that
portion of the works. The assumed temperature of the conductor for the purposes of sagging, will be
determined from an accurate thermometer basket suspended clear of the support steelwork at a point
adjacent to the bottom crossarm level of one support at one end of the span being used to control
sagging. The basket shall have been in position 15 minutes before temperature reading is taken.
However, it should be noted that the maximum conductor tension under the defined system loading
must not be exceeded at the time the transmission lines is handed over. The Contractor shall ensure
that the erection tensions do not exceed the appropriate system loading on the supports. The contrac-
tor’s proposals shall be submitted to the Employer in conjunction with the erection sags and tensions.
The Contractor shall at his own expense make suitable arrangements for temporary guying of sup-
ports where necessary. Suitable plates (detachable or otherwise) shall be provided on the supports
for the attachment of any temporary guys. The additional loads imposed on specific support during
conductor stringing by the use of temporary guys shall be calculated and submitted to the Employer
for appraisal prior to conductor stringing commencing.
The correct sag shall be determined by accurate sighting in the selected span or, in cases where
sighting is considered unsatisfactory by the Employer, another method approved by the Employer
shall be used.
The Contractor shall provide and use a reliable radio communication system to assist in the control of
conductor and OPGW tensioning operation. The conductor/OPGW tensions shall not exceed the ten-
sions determined from the stringing chart.
All conductor and OPGW sagging shall be performed during daylight hours. Sagging operations shall
not be permitted during high wind, or other adverse weather conditions which would impair the accu-
racy of the sagging.
A sag tolerance of 3% will be tolerated but provided all conductors in the span assume the same sag
and the necessary ground clearance is obtained.
The spans adjacent to gantries of Substations shall be slack spans.
Clearances between conductors and ground and between jumpers and all structures are to be
checked during erection and before handing over the line.
The Contractor shall keep a schedule recording all sagging operations showing details of the section,
the sagging and checking spans, ambient temperature, prestress (where appropriate) initial and final
sags, the date of sagging and clipping-in offsets. This record schedule along with the record of com-
pression fittings shall form part of the final records for the line and shall be handed over to the Em-
ployer. The records shall be available for inspection at any time.
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Section VI. Requirements Page VI-60
After this operation, the suspension insulator sets shall be vertical, the tolerance on the sagging de-
flection shall not exceed 15 cm and the tolerance between the deflections of the various conductors of
the same span shall not exceed 7.5 cm.
Transposition of phases
Not applicable for line length lower than 150 km
Obstacles crossing
The Contractor shall provide and install any necessary protection for the crossing of power lines, tele-
phone lines, railways, roads, highways and obstacles and overhanging dwellings, buildings, etc. for
their protection and that of the cables. The arrangements to be made during the work (clearance, sur-
veillance, notification, etc.) shall be taken at the expense of the Contractor and to the satisfaction of
the administrative authorities or private persons concerned, with whom the Contractor will be required
to Report.
Road Crossings
− The time of beginning, duration and technology of safe works on conductors and wire cables
mounting when crossing a highway shall be agreed on with the organization operating this
highway;
− When carrying out the works, the attendance of a representative of this organization is manda-
tory unless denial in writing is obtained;
− In places of traffic, the conductors and wire cables shall be run-out on a scaffolding of at least
6.0.m high;
− At the moment of conductor stringing, care shall be taken to keep people away from and under
the conductors and wire cables;
− At a distance of 100 m on both sides of the scaffoldings, the mounting crew foreman shall place
workers with red flags to warn or stop the transport if necessary;
− Places of work shall be marked with "safety first" signs; and
− Conductor stringing shall not be performed in fog with low visibility, in icing and wind with a
speed over 10 m/s.
Crossings of Transmission Lines
− The Contractor's personnel shall arrange for and attend safety training to get acquainted with
safety regulations being in force in the line operator organization;
− The Contractor shall propose site arrangement scaffolding and their dimensions and locations
for the line mechanical protection during stringing operation. The arrangement shall be ap-
proved by the line operator.
− The works should not start without permit to work signed by the line operator.
− Prior to commencing stringing operation, all towers under the project within in the stringing sec-
tion shall be earthed.
− Stringing may commence only upon the existing line de-energization and suitable grounding in
place. The grounding of existing line shall be performed by the operator's crew demonstrating
the absence of voltage while installing grounding.
− The working areas shall be marked with warning signs.
− The Contractor is responsible of identifying and measuring the span of the existing line to be
crossed (location of towers and cables). It is the Contractor’s responsibility for assuring that the
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Section VI. Requirements Page VI-61
electrical clearance between the existing line and the new line or the construction team will re-
spect EN standards during construction, maintenance and everyday use. Climatic conditions
must be taken into account when measuring the conductor sag of the existing line and measur-
ing clearances.
Scaffolding
Scaffolding shall be provided over roads, power and communication lines, houses etc. The cost of all
scaffolding shall be included in the stringing price.
The scaffolding which is used to cross specified low, medium and high voltage power lines shall be of
such dimensions and allow such clearances that the power lines being crossed may remain in com-
mission during construction of the new transmission line. Shut downs on the lines to be crossed may
be given for construction of new line but shall not be given continuously for longer periods. Such re-
strictions in building and use of the scaffolds shall not be grounds for claiming additional costs.
2.4.8 Specific requirements for the OPGW
General
The Contractor shall determine the position of the splicing boxes progressively as the pegging-out
book is approved by the Employer for each of the lines. The splicing box distribution must be opti-
mized in order to minimize the number of splices while at the same time keeping to the maximum
OPGW length that a drum can contain as specified by the manufacturer.The Contractor shall submit to
the Employer a list containing the location of the boxes, the length of cables between each box as well
as the required quantity of related accessories such as suspension clamps, tension clamps and down-
comer clamps. To determine the length of OPGW required on each drum, the Contractor shall in-
crease the distance between the two towers at the end of the stringing section by a factor of 0.08%
and add the height of these two towers as well as an additional 40 m length for handling and splicing.
Tools and equipment
The diameter and shape of the stringing pulley groove and of the tensioner used for stringing the fibre
optics Earthwire must comply with the requirements of the OPGW manufacturer.
Similarly to the other conductors, the Contractor will use conductor fastening devices or pulling cablets
that, thanks to their ball bearings, prevent torsion effects from being transferred to the cables during
stringing operations. If required by the OPGW manufacturer, the Contractor will install a twisting pre-
vention system between the pulling device of the fibre optics Earthwire and the swivel. This twisting
prevention system must be fitted with a counterweight having sufficient mass to prevent the OPGW
from rotating during stringing.
The Contractor will ensure that the come-along clamps or other hauling devices are of an approved
model that will not damage or unduly bend the cables during their stringing. The use of come-along
clamps with parallel jaws is prohibited for pulling the fibre optics Earthwire. During the OPGW sagging
and tensioning operations, the pulling clamps used shall comply with the requirements of the OPGW
manufacturer.
OPGW down comer and connection of optical fibres
Fastening the OPGW to the towers
When handling and fastening the downcoming OPGW to the tower, a minimum radius of curvature
shall be applied to the fibre optics OPGW as prescribed by the manufacturer.
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Section VI. Requirements Page VI-62
Checking the optical quality of the fibres
After clamping of the OPGW and fastening the downcomer cables but before connecting the optical fi-
bres, the optical quality of the fibres of each line section between two towers fitted with a splicing box
will be checked. For this purpose, an optical reflectometer, commonly known as an OTDR (Optical
Tune Domain Reflectometer), with a wavelength of 1550 nm will be used and the results will be rec-
orded on a plotter.
The OPGW section installed shall be modified or replaced according to the instructions of the Employ-
er if it does not meet the following requirements:
− The measured length of each optical fibre will be the same for each fibre and will correspond
approximately to the cable length plus the correction factor given by the manufacturer;
− The linear optical attenuation value of each optical fibre measured on site must be comparable
with the value originally measured in the factory and must be less than the maximum value
specified in the table of opgw technical characteristics;
− By comparing the backscatter curve of an optical fibre measured on site and the same curve
measured in the factory, no new localised attenuations shall appear.
Preparation of the cable before connection of the optical fibres
The cable will be prepared according to the instructions of the OPGW manufacturer, at the distance
from the end recommended by the splicing box manufacturer. The groups of fibres of each OPGW will
be inserted in the orifices of the box, the connection bushings will be installed, and the optical fibres
will be regrouped in the grouping tubes carrying a label showing the name of the original substation.
All these operations shall be carried out according to the instructions of the splicing box manufacturer.
Connection of the optical fibres
The optical fibres must be connected by fusion. The removal of the protective sheaths and coating of
the fibres, the stripping, splitting and fusion operations must be performed by a qualified team, in a
weather-proof place, with the automatic equipment and tools, perfectly adjusted and calibrated for the
type of optical fibres to be connected.
The maximum attenuation of a fusion coupling must be less than 0.06 dB. Any fusion coupling with an
attenuation greater than 0.06 dB shall be remade a maximum of 4 times. The attenuation value of a
fusion coupling is the mean value of measurements taken in the two directions. To measure the atten-
uation of a fusion coupling, an optical reflectometer (OTDR) with a wavelength of 1550 nm will be
used. The distance between the monitoring site and the fusion coupling site must be less than the re-
flectometer range. In order to take measurements in both directions, at the next box, the optical fibres
from the departure substation will have to be temporarily looped two by two by fusion coupling. These
values must be forwarded to the Employer.
After a fusion coupling has been accepted, a fusion coupling protector will be installed. The plate will
be marked with the origin of the fibres for each of the storage modules by writing the name of the sub-
station and the fusion coupling protectors will be labelled with a number corresponding to each fibre,
according to the colour coding system used for fibres and tubes. The fusion coupling protectors will be
attached in the assembly plate storage modules, the optical fibres will be wound on the plates and the
surplus fibre grouping tubes in the box. Finally, the splicing box will be assembled and closed accord-
ing to the manufacturer's instructions.
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Section VI. Requirements Page VI-63
2.4.9 Drawing up of inspection forms
Two types of inspection forms shall be drawn up:
− Qualitative inspection of towers
− Numerical inspection of sags
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