STRINGING.docx

7/29/2019 STRINGING.docx

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Stringing of transmission lines

5.1 HANDLING OF CONDUCTOR AND EARTHWIRE

i. Handling and transporting of the conductor and accessories shall be carried out in sucha manner as to minimize the possibility of damages from abrasion through roughhandling or dirt and grit and getting into the reel of the conductor by touching or rubbingagainst ground or objects, causing injury to the conductor etc. Particular care shall betaken at all tines to ensure that the conductor do not become kinked twisted or abradedin any manner. If the conductor is damaged, the section affected shall be replaced orrepaired by putting joint or using repair sleeves or polishing with emery cloth, so as togive satisfactory performance.

ii. At all stage of construction proper care shall be taken so that the conductor surface issmooth enough to be given satisfactory corona and radio interference performance. Allequipment 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 contactthe conductor, are kept free of foreign or defects.

iii. Care shall be taken while running out the conductors such that the conductors do nottouch or rub against the ground or objects which could scratches or damage to thestrands. The conductor shall not be over strained during erection. The conductor shallbe run out of the drums from the top in order to avoid damage due to chaffing. Drumbattens shall not be removed until conductor drums are properly mounted at the drumstation on the line, and battens shall be immediately refitted on the drum if any surplusconductor is left thereon. Drums will be transported and positioned on station with theleast possible amount of rolling, immediately after running out, the conductor shall beraised at the supports to the level of the clamps and placed into the running blocks. Thegrooves of the running blocks shall be of a design that the seat is semi-circular andlarger that the diameter of conductor/earth wire and it does not slip over or rubs againstthe sides. The grooves shall be lined with hard rubber or neoprene to avoid damage toconductor 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 constructionproper care shall be taken so that the conductor surface is smooth enough to givesatisfactory corona and radio interference performance.

iv. The running blocks shall be suspended in a manner to suit design of the cross-arm. Allrunning 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 theslings as well as the protective surface finish of the steel work. In case, section towersare used even for temporary terminations, if this be unavoidable, they shall be wellguyed and steps shall be taken to avoid damage. The drums shall be provided with asuitable breaking device to avoid damage, loose running out and kinking of theconductor. The conductor shall be continuously observed for loose or broken strands orany other damage. When approaching end of a drum length at least three coils shall beleft 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 perthe recommendations of the conductor manufacturers. normally, the joints shall be somade that these are not required to pass through running out of blocks, the joints will beprotected with suitable joint protector sleeves.

v. The conductors, joint and clamps shall be erected in such a manner that no bird-cagingover-tensioning of individual wires or layers or other deformation or damage to theconductors shall occur. Clamps or hauling devices shall, under erection conditions,allow no relative movement of strands or layers of the conductors.

vi. Repairs to conductors, in the event of damage being caused to isolated strands of aconductor during the course of erection, if necessary, shall be carried out during therunning out operations with repair sleeves. Repairing of conductor surface shall be doneonly in case of minor damage, scuff marks etc, keeping in view both electrical andmechanical safety requirements. The final conductor surface shall be clean, smooth and

shall be without any projections, sharp points, cuts, abrasions etc.


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vii. Repair sleeves may be used when the damage is limited to the outermost layers of theconductor and is equivalent to the severance of not more than one third of the strandsof the outermost layer. No repair sleeves shall be fitted within 30 m of tension orsuspension clamp or fittings, nor shall more than one repair sleeve per conductor benormally used in any single span.

viii. 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 whichensure complete compliance in this regard shall be used.ix. Derricks shall be used where roads, rivers, channels, telecommunication or overhead

power lines, railways, fences or walls have to be crossed during stringing operation. itshall 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.

x. The proposed transmission lines may run parallel for certain distance with the existing400 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 electromagneticand electrostatic coupling in the pulling cables, conductors and earthwires which thoughcomparatively small during normal operations can be severe during switching andground fault conditions on the energised lines.

xi. The sequence of running out shall be from to down-wards i.e. the earth wire shall be run

first followed by power conductors.After running out the top conductor the conductor at the opposite side at the bottomlevel 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.

xii. Adequate steps to prevent clashing of sub conductors after paying out of conductorbefore spacers/spacer dampers are installed. Care shall be taken that all the two subconductors of the bundle are taken from same conductor supplier and preferable fromthe same batch so that creep behavior of these remains identical during sagging, careshall 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 beensured that minimum trees are cut and that too to the extent permitted by the forest authorities.

5.3 PULLING IN OPERATION

i. Before the commencement of the stringing, initial and final stringing charts for theconductor and earth wire showing the sags and tension for various temperatures and spansalong with equivalent spans in the lines should be available. The stringing shall be done as perapproved stringing charts.

ii. The earth wire shall be strung and securely clamped to the towers before theconductors are drawn up in the order of the top conductors first, then the conductor on theopposite side and in the end the lower conductor at the same side. it shall be ensured that allthe conductors of one section should have identical tension time history.

iii. The pulling of the conductor into the travellers comprising of serial and ground rollersshall be carried out in such a manner that the conductor is not damaged or contaminated withany foreign substance and that it may not be rubbed with the rough ground surface, or itdamages the standing crops. For this the height of ground rollers shall be fixed in such amanner that the conductor/earthwire does by douching. The travellers shall have size andshops most suitable for the type of stringing and size of conductor involved and asrecommended by the conductor manufacturer. These shall be approved by the supervisionEngineer before use. The travellers surface in contact with aluminum surface of conductor shallbe 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. Theyshould be inspected daily for free and easy movement in blocks during stinging and sagging.

iv. 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. Afterbeing pulled the conductor and earthwire shall not be allowed to hang in the stringing blocks formore than 96 hours before being pulled to the specified sag. During the time the conductors and


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earthwire are on the stringing block before sagging in, It shall be ensured that the conductorsand earthwire are not damaged due to clashing vibration or other causes.

v. The tensioning and sagging shall be done in accordance with the approved stringingcharts before the conductor and earthwire are finally attached to the towers through theearthwire clamps for the earthwire and insulator stings for the conductor. Dynamometer shall beemployed for measuring tension in the conductor and earthwire. The dynamometers employed

shall be periodically checked and calibrated with a standard dynamometer.For 400 KV lines the following additional precautions shall be taken

i. The stringing of the conductor shall be done by controlled tension method by means oftension stringing equipments. The earthwire may also be strung by the same method. Theequipment shall be capable of maintaining a continuous tension of not less than 10,000 kg perbundle 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.

ii. Controlled stringing method suitable for simultaneous stringing of the sub conductorsshall be used. All the power conductors making one phase bundle shall be pulled in and paidout simultaneously. The two power conductors of the bundle shall be of matched length and ofthe same manufacturer and batch to ensure that the two conductor making one phase haveidentical tension characteristics. After being pulled the conductor/earthwire shall not be allowedto hang in the stringing blocks for more than 96 hours before being pulled to the specified sag.

iii. Necessary arrangements should also be made for paying out the pilot wire for stringingof conductors and earthwire by helicopter in line route where dense forests are involved andpaying out of pilot wire by conventional method is not possible.

iv. The complete details of the stringing method which are proposed to be followed shouldbe planned and decided. Before the commencement of the stringing the stringing charts for theconductor and earthwire showing the initial and final sags and tension for various temperaturesand spans along with equivalent spans in the lines should be got prepared, checked andapproved.

v. During paying out of conductor and earthwire and also during stringing in forest area, itshall be ensured that minimum trees are cut. If required 4 meters extension to towers may beused to obtain proper clearance. If necessary, earthwire shall also be strung by tension stringingequipment 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 throughhelicopter as detailed.

vi. The conductor and earth wire shall be sagged in accordance with the approvedstringing charts before they are finally attached to the towers through the earth wire clamps forearthwire and insulator strings for the conductors.

vii. The conductors shall be pulled up to desired sag and left in travellers for at least onehour after which the sag shall be rechecked and adjusted, if necessary, before transferring theconductors from the travellers to the suspension clamps. The conductors shall be clampedwithin 36 hours of sagging in. The adjustment in sag for creep age of conductor should also bemade before finally clamping,

viii. The sag will be checked in the first and last span of the section in case of sections uptoeight spans and in one intermediate span also for section with more than eight spans. Anydamage to the towers or the conductors through over stressing during stringing shall beawaited.Dynamometers shall be used in checking the tension in the conductors and earthwire and theseinstruments shall be periodically checked with a standard dynamometer. The sags shall also bechecked when the conductors have been drawn up and transferred from aerial blocks to theinsulator clamps.

ix. The stringing blocks, when suspended on the transmission structure for sagging, shallbe so adjusted that the conductor on the travellers will be at the same height as the suspensionclamp to which it is secured.

x. At sharp vertical angles the sags and tension shall be checked on both sides of theangle. The conductor and earthwire shall be checked on the travellers for equality of tension onboth sides. The suspension insulator assemblies will normally assume vertical positions, when

the conductor is clamped. Sagging operations shall not be carried out under wind, extremelylow temperature or other adverse weather conditions which prevent satisfactory sagging.


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5.5 CONDUCTOR DAMAGE AND REPAIR

i. If the conductor is damaged for whatever reason and the damage is not repaired byrepair sleeves or emery cloth, the same shall not be used. Repairing of conductor surface shallbe done only in case of minor damages, scuff marks etc. which are safe from both electrical andmechanical 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.

5.6 JOINTING

i. All the joints on the conductor or the earthwire shall be of compression type inaccordance with the recommendations of the manufacturers, for which the necessary tools andequipments like, compressors and dies, grease gums presses etc, shall have to be arranged bythe contractor. These joint will be made in the best workman like manner, shall be perfectlystraight and having maximum strength. Each part of the joints shall be cleaned by wire brush tomake it free of rust or dirt etc, and properly greased before the final compression is done withthe compressors.

ii. All joints or splices shall be made at least 30 meters away from the structures. No jointsor splices shall be made in spans crossing over main roads, railways, small rivers or in tensionspans. Not more than one joint shall be allowed in one span. The compression type fittings usedshall be of the self centering type or care shall be taken to mark the conductors to indicate whenthe fitting is centered properly. During compression or splicing operation the conductor shall behandled in such a manner as to prevent lateral or vertical bearing against dies. Care shall betaken 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 andsmoothened.

5.7 CUPPING-IN

i. Clapping of the conductors in position shall be done in accordance with therecommendations of the manufacturer. Conductor shall be fitted with arm our rods where it ismade to pass through suspension clamps and with vibration dampers at all the suspension andtension points, as recommended by the manufacturer.

ii. The jumper at the section and angle towers shall be formed to parabolic shape toensure maximum clearance requirements. Clearance between the conductors and ground andbetween jumpers and the tower steel works shall be checked during erection and beforehanding over the line. If pilot suspension string is used with jumpers, the same shall be clampedwith jumper.

iii. Fasteners in all fittings and accessories shall be secured in position. The security clipshall be properly opened and sprung into position.

5.8 FIXING OF CONDUCTOR & EARTHWIRE ACCESSORIES

i. Vibration dampers, arm our rods and other conductor and earth wire accessories shallbe installed as per the design requirement and as per the respective manufacturer'sinstructions. The Vibration dampers, spacers and spacer dampers shall be provided at bothends of each span at suitable distance from the supporting points for each conductor/earthwireas per recommended practice and placement charts of manufacturer. Spacers/Spacer dampershall be fitted within 24 hours of conductor clamping while installing the conductor and earthwire accessories proper care shall be taken to ensure that surface are clean and smooth and nodamage shall occur to any part of the accessories.

5.9 FINAL CHECKING, TESTING & COMMISSIONING

i. After completion of the works, final checking of the line shall be done to ensure that allthe foundation works, tower erection and stringing have been done strictly according to the


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specifications and approved by the supervising Engineer. All the works shall be thoroughlyinspected keeping in view the following main points -(a) Sufficient backfilled earth is lying over each foundation pit and it is adequately compacted.(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 andfree 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 andtension charts and desired clearances are clearly available.(f) No damage minor or major to the conductors, earthwire accessories and insulator strings stillunattended are noticed and rectified.

ii. After final checking the line shall be tested for insulation in accordance with testsprescribed. All arrangements for such testing or any other test desired shall be done. Any defectfound out as a result of such tests, shall be rectified.

iii. In addition to the above it shall be ensured that the total and relative sags of theconductors and earthwire are within the specified tolerances. Such tests shall be carried out atselected points along the route as deemed necessary.

iv. After satisfactory tests on line, the line shall be energised at full operating voltage.

River Crossings of Transmission Lines

GENERAL

River Crossing involved in any Transmission line, is most important link of the line. It has to besafe & sound from design considerations to take care of field conditions, vagaries of naturesuch as cyclones/storms, whirl winds, flood & change of course of rivers etc.

SITE SELECTION

The River Crossing site should be selected judiciously and carefully. It is desirable to crossrivers where :

i. River is tamed by a bridge, preferably on down stream side to avoid fury of floods.ii. River banks at the crossing point are at a level higher than the HFL recorded to

ensure safety of Rx towers during floods.iii. Special well or pile foundations should be avoided as far as possible to minimize the

cost.iv. The soil is firm & dry.v. The river crossing span should be within the maximum designed span of Rx Towers.

TYPE OF RIVER CROSSING TOWERS

The major River crossings should be done on Suspension Type Towers, suitably designed forall wind conditions i.e. for transverse load incorporating wind load depending upon the heightof the tower and upon the height of clamping point of Conductor and Earth wire, Vertical load,and longitudinal load including the effect of diagonal wind (at 45) load conditions. The 'AnchorTowers' designed for Dead-end conditions should be provided on both the sides of crossingas shown below


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Fig. 10-I

DESIGN CRITERIA

10.4.1 The main points considered for design of River Crossing and Anchor

towers are described below :

i. The normal Transmission Line Towers are designed with theassumption that wind would be acting on conductor, Insulator &tower structure in longitudinal transverse direction. But, for very hightowers/structures of river crossing, the load on towers is evaluatedafter taking into account height factor and basic wind pressure etc.The towers for river crossing should be designed for diagonal windload conditions also, which is an additional feature to take care ofhigh velocity winds during severe storms/cyclones etc. Behavior ofwind will, however, depend on the river crossing locations and theprofile of crossing.

ii. The towers are so designed that the minimum factor of safety of

individual member as well as over all structure is not less than 2.5. iii. Shielding angle is; less than 30 for 132 KV and 220 KV towers and

20 for 400 KV towers.iv. Over load factor for vertical loads is taken as 1.29v. The wind on, towers is assumed to be acting at an angle to the line

which may produce the maximum combined effect of conductor andtower loadings in the tower members.

vi. Longitudinal load under broken wire condition due to powerconductor and ground wire for Rx towers is taken as 100% of thetension of conductor and ground wire at 32C with no wind. This ismultiplied by Impact Load Factor of 2.65.

vii. Broken wire conditions should be assumed as follows :

a. Suspension Towers (Rx Towers):Ground wire or any one conductor broken whichever is morestringent for a particular' member in the tower.

b. Anchor TowersDead-end type towers designed for any combination of ground wireand two conductors on the same side or three conductors on thesame side and on the same span whichever is more stringent for aparticular member in the tower.

PARAMETERS

The main desirable features/parameters are being described brieflyhereinafter :

1. River Crossing Towers (Rx Towers)

I. The main design parameters for River Crossing (Rx) Towers which should be clearlyspecified and whih are presently being used in UPSEB are as follows:

132 KV 220 KV 400 KV

(a)Deviation angle 0 0 0

(b)Wind span maximum under normal Conditions 600 m 824 m 750 m

(c)Weight span 1000 m 2700 m 1100 m(d)Designed maximum crossing span 525 m 1160 m 800 m


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(e)Clearances from highest flood level (Minimum) 6.1 m 7.0 m 8.84 m

(f) Conductor code name Special ACSR'PANTHER'

Special

ACSR

'DEER'

Twin Bundle

'ACSR'

MOOSE

(g)Ground wire size and quality 7/3.25 mm GSwire, 95 kg/sq.

mm Quality

7/3.66 mm

GS

wire, 110

kg/sq.

mm Quality

7/3.66 mm

GS

wire, 95

kg/sq.

mm Quality

(h)Double Suspension Insulator Strings(Em Strength and total maximum length of

insulator should be specified clearly).

70 KN, 2073

mm120 KN,

2860 mm120 KN,

3355 mm

(i) Wind Pressure-

(i) on Conductor 100 kg/sq. m 220 kg/sq.m

1954 Kg/sqm

(ii) on Ground wire 100 kg/sq. m 225 kg/sq.m

205 Kg/sqm

(j) Temperature variation for whichtowers are designed-

(i) Maximum 65C 75C 75C

(ii) Minimum 0C 0C 0C

(i ii ) Everyday 32C 32C 32C

II. The Salient features of Rx Towers presently being used in UPSEB are as follows:

132 KV 220 KV 400 KV

(a)

Total height above GL (M)

49.470

108.200

98.100(b) Height of the bottom cross arm

from GL34.270 88.600 67.000

(c) Height of middle cross armfrom GL

38.870 95.600 78.000

(d) Height of the top cross armfrom GL

43.470 102.600 89.000

(e) Base width 5.5 15.486 18.000

(f) Width of cross-arm

(i) Bottom 8.400 11.200 15.400

(ii) Middle 8.000 10.200 14.700

(iii) Top 8.000 9.700 14.700

(g) Weight in MT

(i) Normal towers 10.218 73.448 82.377

(ii) Hangers 0.015 0.010 --

(iii) U-bolts (kg) 0.970 0.930 --

(iv) Pack Washers (kg) 0.017 0.017 0.349

(v) Stubs & Cleats 0.631 3.021 3.347

(vi) Ladder & Platform -- 4.120 11.237

(vii) Rungs --- 0.248 --

(viii) Bolts & Nuts 0.408 2.826 1.541

(ix) Total weight 11.290 83.852 98.852


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If the Rx Towers are located in the meandering zone of, the river, SpecialWell-Type or Pile-type foundations are provided. However, with normal orwet soil with unit weight of 940 Kg per Cu. Meter and bearing capacity of13675 Kg per Sq. Meter assuming angle of repose as. 15 the open castfully submerged RCC Foundations (Step type) should be provided.

2. Anchor Tower

I. Main features of Anchor Towers which are presently being used in UPSEB are asfollows :

132 KV 220 KV 400 KV

(i) Total height above GL 30.415 46.245 50.145

(ii) Height of bottom cross-armabove GL

15.535 21.845 22.110

(iii) Height of middle cross-armfrom GL

19.585 28.395 32.110

(iv) Height of top cross-arm fromGL 23.485 34.945 42.110

(v) Base width 7.600 12.746 17.500

(vi) Weight in MT

(a) Towers 7.045 20.507 27.505

(b) Stubs 0.617 0.999 1.237

(c) Pack-Washers 0.199 0.195

(d) Bolts & nuts 0.273 0.575 0.736

(e) D-Shackle 0.0097 0.019

(f) Extension link 0.029 0.033

(g) Total weight 7.935 22.164 29.720

(vii) Designed wind span in meters 380 380 400

II. Foundations for Anchor TowersAnchor towers are desirable to be placed outside meandering zone of the rivers. Insuch cases the foundation normally provided is open cast fully submerged RCC

(Step type).

DEVIATION ON RIVER CROSSING TOWERS

10.6.1 No deviation is allowed on River Crossing Towers. All the towers

from Anchor Tower to Anchor Tower on River crossing portion should be instraight line. The Anchor Towers should be placed square to River crossingportion. If any deviation is required to be given, it should be given on thenormal line side only.

CALCULATION FOR IMPORTANT PARAMETERS

10.7.1 Position and method for calculations of following parameters are alsoenclosed for reference & guidance :


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a Sag & Tension Annexure-1

b Ground Clearance Annexure-2

c Uplift on Anchor Towers Annexure-3

d Stringing Charts Annexure-4

GUIDELINE FOR PREPARATION OF PROPOSAL FOR RIVER CROSSING

The river crossing proposal should be submitted from the field coveringfollowing details :

A. PROFILE:

i. Profile of river crossing and Anchor towers along with position ofadjacent towers of the line of either side of the river crossing.

ii. The profile should clearly indicate reduced level of HFL mark, Rxand Anchor tower locations, nearby roads, bunds/embankment etc,if any.

iii. The year of HFL mark and source of information.iv. Sag curve of 75C and no wind for each span from Anchor to

Anchor towers.v. Clearance of lowest power conductor from HFL mark for maximum

sag calculated at 75 and no wind. The minimum clearance requiredis 6.1 meters for 132 KV, 7.00 meters for 220 KV and 8.84 metersfor 400 KV lines for non-navigable rivers.

B. PLAN:

i. Plan showing Rx Towers, Anchor towers, adjacent tower with span,roads, bridges, bunds and other important structures etc.

ii. Type of soil and its bearing capacity.iii. Meandering zone of the river.iv. Whether Rx and/or Anchor towers will remain normally submerged

in water, should also be indicated clearly.

C. CALCULATIONS FOR UPLIFT :

On Anchor towers shall also be submitted on the profile & plan sheet itself.

D. NARRATIVE:

Narrative about the geographical conditions of the area and whether therewould be any problem for right of way etc. should also be submitted alongwith the proposal.

PRECAUTIONS DURING CONSTRUCTION WORK OF RIVER CROSSING :

1.The following points may be borne in mind and implemented religiously before takingup construction activities for river crossing

i. The tower parts should be checked with approved drawings and billof material (B.O.M.) about correctness of fabrication and supply.

ii. The survey and profile should be thoroughly checked at site. Itshould be ensured that the river crossing portion from Anchor-to-

Anchor are in straight line. No deviation is allowed on River


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Crossing Towers and anchor towers on the river crossing side, i.e.the anchor towers should be placed square to the river crossingportion.

During construction right from survey to final sagging and commissioning.The following precautions may be taken to ensure execution & completion of

River Crossing properly from all considerations :

A. DURING FOUNDATION:

i. The pits should be as per approved drawing.ii. The template should be placed and installed

properly as per drawing for proper setting of stubsand the following dimensions should be checkedbefore concreting: -

a. Base widthb. Base Width (back-to-back)c. Diagonals

iii. Proper Form Boxes or moulds should be used. Ifnecessary shoring and shuttering should be used toavoid falling of surrounding earth and its mixing withconcrete.

iv. Depending on the condition, proper arrangementshould be done for dewatering of pits, preferably bypower driven pumps.

v. The concrete in 1:2:4 ratio should be mixed inmechanical mixer, preferably power driven. Handmixing should not be allowed.

vi. Proper laying and filling of concrete should beensured. It should be done continuously, uniformlyand properly with power drive vibrators.

vii. The concreting of a particular leg should be donecontinuously and uninterruptedly to ensure properbonding.

viii. It is also preferable that concreting of 2 diagonallyopposite legs is done simultaneously.

ix. The levels of all the 4 legs should be checkedbefore concreting during concreting and aftercompletion of concreting job also.

x. The curing should be done properly andcontinuously for a period of at least 10 days.

xi. Proper back filling by the same soil should beensured.

xii. The stub setting template should be opened onlyafter the back filling.

B. DURING ERECTION OF TOWERS :

i. The erection work should be done panel wise asper drawing.

ii. It should be ensured that all the bolts & nuts ofcorrect sizes are provided on all the members asper drawings and no hole is left blank.

iii. All the cleats, gusset plate and pack washersshould be provided as per drawing.


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iv. After erection of each panel and sections, the levelsand verticality should be checked and correctivemeasures be taken, if necessary.

v. If the erection of tower is partial then it should beanchored properly and suitably before resumingwork on next day.

vi. After completion of erection each & every boltshould be tightened properly and checkedthoroughly.

vii. Punching & hammering of left over threads shouldbe done.

viii. Insulator strings should be assembled on theground and hoisted properly before stringing.Chipped or cracked insulators should not be used.

C. DURING STRINGING:

i. Before stringing it should be ensured that all the bolts & nuts have beentightened and punching and hammering of the left over threads has

also been done.ii. The placement of Rx & Anchor Towers has been done as per approved

survey and profile and that all the towers of River Crossing portion fromAnchor to Anchor are placed in straight line i.e. square to the rivercrossing portion. It may be noted that no deviation is permitted.

iii. River Crossing span is as per approved profile and within the maximumdesigned spans.

iv. Levels & verticality of all the towers is Okay.v. The stringing should be done as per standard norms & practices by

using ground rollers, aerial rollers (with high quality Ball rollers forminimum friction), Snatch Pully Blocks, Hydraulic pressures, proper T &P and equipment, preferably by Tension Stringing Equipment.

vi. It should be ensured that E/W is strung and securely clamped to thetower before the conductors are drawn up in the order of top conductorfirst then the middle and bottom conductors at the end.

vii. It is also desirable that paying & tensioning of both the conductors on aparticular cross arm is done is simultaneously, so as to maintainidentical tension time history.

viii. The traveler surface in contact with aluminium surface of conductorshould be of such a material that the conductor is not damaged due tocontact with material such as neoprene rubber or Stainless steel.

ix. The conductor should not be rubbed with any rough ground surfaceand it should not also damage the standing crops.

x. During pulling out operation the tension in each conductor and E/Wshall not exceed designed working tension of the conductor at theactual prevailing temperature.

xi. After being pulled the conductor and E/W shall not be allowed to hangin the stringing blocks for more than 96 hours before being pulled to thespecified sag. During the time the conductors and E/W are on thestringing block before sagging in, it should be ensured that theconductors and E/W are not damaged due to clashing, vibration orother causes.

D. FINAL SAGGING:

i. The conductors and E/W shall be sagged inaccordance with the approved stringing chartsbefore final clamping. The conductors shall be

pulled-up to the desired sag and left in travelers atleast for one hour after which the sag shall bechecked and adjusted if necessary before


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transferring the conductors from the travelers to thesuspension clamps.

ii. The conductors shall be clamped within 36 hours ofsagging in.

iii. Clamping as per initial stringing chart.iv. Dynamo-meters should be used in checking the

tension in the conductors and EAV.v. The sage shall also be checked when theconductors have been drawn up and transferredfrom aerial blocks to the insulator clamps.

vi. Sagging operations shall not be carried out underwind, extremely low temperature or other adverseconditions which prevent satisfactory sagging.

E. FINAL CHECKING, TESTING & COMMISSIONING :The following points should be kept in view beforecommissioning

i. Sufficient backfilled earth is lying over each

foundation pit and it is adequately compacted.ii. Concrete chimneys and their copings are in good

and finally shaped conditions.iii. All the tower members are correctly used strictly

according to finally approved drawings and are freefrom any defect or damage, whatsoever.

iv. All the bolts are fully tightened and they areproperly punched.

v. The stringing of the conductors and earth wire hasbeen done as per the approved sag tensions chartsand desired clearances are available.

vi. No damage, minor or major to the conductors, earthwire accessories and insulator strings, stillunattended are noticed.

ANNEXURE- 1

SAG AND TENSION CALCULATIONS FOR CONDUCTOR/EARTH WIRE FORRIVER CROSSINGS

ANNEXURE- 2

METHOD FOR GROUND CLEARANCE CALCULATIONS FOR RIVERCROSSINGS

ANNEXURE- 3

METHOD FOR WEIGHT SPAN CALCULATIONS FOR RIVER CROSSINGS

ANNEXURE- 4

STRINGING CHARTS FOR RIVER CROSSINGS

Sag and Tension Calculations For Conductor/Earth Wire ForRiver Crossing

Sag and tension calculations for conductor earth wire are done for the river crossingby following steps :

i. Determination of Equivalent Span :Based on anchor spans L1 & L3 and crossing span L2, the equivalent span for rivercrossing portion is determined by the following formula :

Eq. Span = L13+ L2

3+ L3

3/ L1

+ L2

+ L3 (Refer Figure 10-II)
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ii. Sag and tension calculation for conductor/earth wire for above equivalent spanis done from the following formula :T

2(T - K + aEa (q2-q1)) = W

2L

2aE / 24 x q

2

where,T = Tension at temperature q2 (kg)K= Constant

a = Area of conductor/Earth wire (mm2

)E = Modulus of Elasticity kg/mm

2

a = Linear Coeft. of expansion (per degree celcius)W = weight of conductor (kg/m)L = Equivalent span (m)q = Wind load factor = P

2+ W

2/ W

2= 1 (At no wind condition)

q1 = Initial condition temperatureiii. Calculation for conductor

a. Initial condition for conductor is taken as 32C and No wind and T0tension under these conditions is taken as 22% of ultimate tensilestrength of conductor.

b. From the above value of T0, we calculate the constant'K

which isfixed for all further sag-tension calculations.c. Considering the calculated value of K, the tension at 0C under No-

wind & full wind and 32C full wind and 75C No-wind is determinedfrom the above formula by hit & trial method.

d. Sag at various tension := WLA

2/ 8T where LA is actual span

iv. Calculation for Earth wire

a. The earth wire sag at 0C and no-wind should be 90% of theConductor sag at 0C and No-wind. Value of tension at 0 and no

wind is determined by the following formulaT = {WL

2/ 0.9 x Sag of Conductor at 0

0N/W}

for equivalent spanwhere L = Equivalent span in meters.

b. As in the case of conductor, the tensions at 0C (No-wind & full windCondition), 32"C full wind conditions and 75C no-wind condition aredetermined.

c. Sag = [WLA2/ 8TA] where LA = Actual span.


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Fig. 10-II

Method For Ground Clearance Calculations For River Crossings

Method for ground clearance calculations for river crossings

Ground clearance in the crossing span is determined from the following formula :

a. a = L / 2 + TH / WLwhere,a = Distance of lowest point of wire from higher tower.L = Actual spanT = Tension at 75

0C & N0-wind for equivalent tower.

h = Height difference of two river crossing towers.W = Weight of conductor / meter (kg / m)

b. From a, span 2a is calculated and sag SA for River crossing span this span isdetermined as per following formula.SA = [2a / Eq. Span]

2x Sag at 75

0N/W for equivalent span.

From above, the max sag is determined by adding 4% error in sag to theabove.

c. R.L. of Null point is determined as follows :R.L. of Null point = R.L. of bottom cross arm of higher 'Rx' tower after deductinglength of insulator string & length of cleat and D-shackle and maximum Sag.Ground clearance available= (R.L. of Null point - R.L. of H.F.L.)

d. Method For Weight Span Calculations For River Crossingse.f. Method for weight span calculations for river crossingsg. Weight span calculations for various anchor towers and river crossing towers

are done as follows :h. a = L / 2 + Th / WLi. where,

L = Considered anchor crossing span in meters.T = Tension at 0

0C No=wind for equivalent span under normal condition or 32

0

F/W for worst condition in kg.h = Height difference with respect to adjacent tower in meters.

j. The negative value of 'a' for anchor spans determines the uplift on the anchor

tower. The uplift in kg is determined by multiplying the above uplift (in meters)by the weight of conductor/meter. Uplift on a tower up to the limit which can beencountered by the weight of insulator string can be allowed without providingany reinforcement on cross arms of towers.

Stringing Charts For River Crossings

STRINGING CHARTS FOR RIVER CROSSINGS

a. Final stringing charts are prepared on the basis of sag and tension calculationsat different temperatures under no-wind condition for a particular proposal as

per Annexure-1. These charts give final values of sag and tension which should


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never be exceeded on a line.

b. The stringing should be done as per initial stringing charts which are preparedafter taking into account creep correction for the conductors. For earthwire nocreep correction is required.

c. The stringing charts for river crossings are prepared from anchor tower toanchor tower only.

d. Sag indicated in the stringing charts are with respect to higher tower isdetermined as follows for cases where there is level difference between twotowers.Sag at span = {2a / L}

2x Sag at particular temperature for crossing span.

where,a = L / 2 + TH / WLwhere,L = Crossing span Cm)T = Tension at particular temperature under No-wind for equivalent span (kg)h = Difference of R.L. of towers, (m)

W = Unit weight of conductor/Earth wire. (kg/meter)

e. For cases where there is no level difference, the value of sag given in thestringing chart for the corresponding crossing span may be adopted

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