Method statement for transmission line (lanco)


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Method statement for transmission line (lanco)

  2. 2. METHODS ADOPTED FOR CONDUCTOR INSTALLATIONS IN 765 KV T/L a)Mechanized Paying out of conductors and installation Manually b)Manual Paying out of conductor and its manual installation. TYPE OF RISK ASSOCIATED: a)Fall of workmen from height b)Fall of objects from height, on workers and co-passers – by c)Collapse of towers, conductors and hardware Fittings on workers and passers –by d)Electrocution due to contact of person / Conductors with live wires e)Hit by Vehicles (Workmen and co passers-by) CONSEQUENCES OF ACCIDENTS: a) Fatality / Injuries to workers
  3. 3. b) Fatality / Injuries to co-passers by c) Loss to properties including public property d) Lost of man-hours resulting in time and cost overruns e) Public resentments, disgrace f) Punishment under the relevant laws
  4. 4. VARIOUS STAGES OF WORK IN THE INSTALLATION OF CONDUCTORS IN TRANSMISSION LINE a) Insulator and aerial roller hoisting b) Paying out of pilot wire c) Paying out and sagging of Earth wire. d) Paying out of conductor e) Rough sagging f) Final sagging g) Clipping and fixing of line spacers h) Fixing of jumpers i) Stringing of river crossing reaches j) Power line crossing k) Stringing across Highways and other service roads l) Transportation and stacking of conductor drums and Hardware fittings
  5. 5. HAZARDS ASSOCIATED AT VARIOUS STAGES OF WORK: SL NO HAZARD INVOLVED REMEDIAL MEASURES CHECK POINTS . ACTION BY PERIODICITY REMA RK INSULATOR AND ARIEAL ROLLER HOISTING 1. a) Fall of workmen from a) *Use of fall arrester must be ensured for cross arm sitting location making vertical movement over tower. or * Proper use of double lanyard type full body while ascending and descending over tower. harness shall be ensured. b) Fall of insulator string or b) * Proper fixing of cotter pins/split pins must other tools and tackles. his maneuvering. Hit injury Injury while or crush handling insulator boxes and heavy aerial rollers. SITE A) *Fall arrester. A) REGULAR The ENGINEER And for each most * Good condition / GANG insulator string hazardo double lanyard Safety LEADER hoisting. us belt. aspects b) * Availability of of be ensured before hoisting insulator string. 12mm dia wire rope as b) REGULAR insulato * Check the wire rope (12mm) being used for a lifter. And for each r insulator string hoisting for any type of visual c) Hit by tractor in path of d) CHECK FOR--- * Good condition single insulator string hoisting sheave pulleys of hoisting. is when damage. * Before hoisting proper working condition both bearing type only. workme * Additional safety c) REGULAR n uses rope used foe securing For every road to get also only bearing type pulleys shall be used. single sheave pulleys crossing down * if open hook type single sheave pulleys are of open hook type. being used , then additional safety rope shall be * Good condition D) Regular and insulato used for avoiding its accidental release. 16mm dia wire rope for every lot of r string * only 16mm dia wire rope sling should be used sling. insulator boxes. for the single sheave pulleys shall be ensured and for securing single sheave pulleys with tower members provided , precautions has been taken against sharp edges of tower members. through * License and driving releasin skill of operator/ g guide driver. rope IMPORTANT CHECK: tied * Check for proper connection of aerial roller 1. with with insulator string. hoisting tower erection bottom 3. Always avoid bending of insulator string while must be complete in all yoke hoisting i.e. P.P rope or wire rope shall be tied regards. plate or with 3 2. rd or 4 th insulator disc from top. Bending of Before more insulator importance shall be given to cross with aerial
  6. 6. insulator string may lead to failure of R-clips. arm c) connecting * Only licensed and well trained driver shall be engaged for operating tractor, used for insulator string hoisting. i.e all the bolts roller. and tower members must be in properly intact condition. * If at all any road crossing exist in maneuvering path of tractor, presence of ‘ SIGNALMAN’ must • be ensured . Maneuvering path of d) *Over height stacking of insulator boxes • shall be avoided at location. * Wooden planks having nails shall be kept well away from site to avoid nail prick. *WEARING OF SAFETY HELMET AND SAFETY SHOE IS MUST BY ALL PERSONNELS IRRESPECTIVE OF NATURE OF JOB. COMMAN PRACTICE: it is very common practice of using step bolts, in D-shackles and in aerial roller assembly , which are not meant for heavy loading and always suspected to failure. PAYING OUT OF PILOT WIRE 2. a) Minor cut injury to A) Periodical visual inspection of pilot wires Condition of pilot wire fingers due to for wear and tear and other visual damages Condition of P.P rope Site protruding wires of pilot shall be done. being used Engineer Effective Use of PPE’s / Gang wire. B) Use of leather type hand gloves shall be Jhulla arrangement Leader b) Fall of workmen from ensured to minimize the severity in case of IMPORTANT CHECK: it cross such incident. is generally noticed arm position/ that local lineman uses aerial roller (for passing C) Use of double lanyard full body hare ness P.P rope through roller) shall be insured. 11kv and 33kv power Or Double arrangement for ascending over lines and fitters of insulator string shall be done as follows— stringing gang uses to otherwise ascending during and descending over tower. D)) Lanyard of safety belt shall be wrapped to give shutdown of lower the conductor after de-energizing the
  7. 7. c) Hit injury while around the insulator string. line. Following min. pilot drum E)) Jhulla arrangement made of 20mm P.P precautions must be handling ensured in such reel. rope, controlled from ground shall be used. D) Over turning of F) Regular pep talk shall be done and 1. be perfectly sure tractor while awareness should be created among about distribution transporting pilot drum workmen regarding safe handling & feeder (of the reel. transportation of pilot drum reel. E) OTHERS: F) Pilot wire connectors shall be checked 2. Ensures the does not 1.pilot wire connectors: for any type of visual damages in – have any looping with Pin and its threaded portion other line near by and Roller & U-portion operations--- particular line) , installed in substation . then decide the point of opening jumpers. 2. eye splicing in pilot G) Visual checks shall be done for condition ( views of local people wire of eye loops made in pilot wire before every must be taken use. regarding the rout and interconnection of line) 3. Power line / road or H) Obtain proper shutdown before lowering highway crossing the conductors of any line crossing. jumpers ensure the (chances of I) Proper scaffolding capable of bearing line is discharged electrocution / injury to load of pilot wire and conductors shall be through bundling the co passers. made for every P&T and road crossing. 3. Before opening the conductors by passing a p.p rope over it. J) Suitable warning signs with signalman 4. Ensure the use of (equipped with walky-talky) shall be hand gloves meant for deployed at every road crossing irrespective working on HV/EHV of its type and users. lines. 5. The conductors shall be lowered and kept in bundled condition. PAYING OUT OF CONDUCTOR POSITIONING OF TSE MACHINES
  8. 8. — machine to a long distance. Toppling of machine B) Check air pressure and find out the suitable while shifting/placing 3. A) Proper care shall be exercised while shifting approach road for shifting. C) While shifting no workmen shall be allowed ride over it. D) Well-experienced tractor driver shall be taken for the task. E) TSE machines shall be properly anchored with dead-end anchors in the ground. The preferable angle with ground should be 45* or less. F) The puller shall be placed at a distance (from Ist normal tower), not less than three times the tower height. PRE PAYING OUT CHECKS 4. A) DRUM POINT Site Engineer / TSE operator / gang leader Hit injury to workmen
  9. 9. A) Hand gloves shall be used while handling wire IMPORTANTCHECK: A) while placing two ends meshed single/ double end shocks. place and single ends shocks. B) Watch out for protruding wires, and removes drums at least 30 M B) Hit injury or cut the same by cutting plier and if the wire mesh is injury while placing severely damaged replaces it with new one. drum lifting jack or C) Place the drum-lifting jack on firm and level conductor drums. ground to avoid is toppling. C) Failure at headboard D) Never replace drum-mounting shaft with any machine is smooth and assembles point. other inferior means such M.S or tor steel used free from obstruction. for reinforcement work. Use only recommended C) The area between connectors only in drum lifting jack. drums E) Check the Physical condition and load bearing machine must be kept capacity (from test certificate of supplier) of swivel joints (articulated joints) provided behind Headboard. F) Check the condition of wire rope and single end wire meshed shocks before applying the load. G) place suitable capacity D-Shackles at each joint. PULLER POINT the conductor back to the tensioner machine. B) Check weather the conductor release from drum and entry into barricaded and to TSE avoid unauthorized entry. SITE ENGINEER / GANG LEADER A) Cut injury in fingers
  10. 10. A) Proper personnel precautionary measures while handling pilot wire shall be ensured in pilot wire reel (while reel. removing from puller machine after complete B) hit injury/hit injury binding). while handling SITE ENGINEER /GANGLEADER A) Cut injury in fingers --Same as above-- ( loading/unloading) of pilot wire reel. GUYING OF DEAD-END TOWER Failure guy The make-up end tower shall be properly guyed IMPORTANT anchorage or guy rope before with the help of 18mm dia wire rope and angle of turn shall be itself in deadment anchor. The tightening of turnbuckles maintained damage of tower (cross- shall be done carefully to avoid extra loading on arm) cross arm. Pit for dead ment, standards of Fall of resulting of person height while from logwood shall be maintained as mentioned above. CHECK: for guy rope according to the turn of line . angle of guy rope shall not be more than 45* with cross arm. Ensure use of fall arrester for ascending and Ensure effective tying descending over tower. of wire rope with cross Ensure use of double lanyard full body harness arm. while working at height. Ensure use of lifeline for making horizontal movement over cross arm. PAYING OUT OF CONDUCTOR TIGHTIENING OF PILOT WIRE FROM PULLER END
  11. 11. This is the most critical & hazardous IMPORTANT TO WORKMEN AND activity of machine paying out operation. It SIGNALMAN WITH RED SIDE PASSERS, is well known that pilot wire are laid on ANIMALS & ground through out entire section proposed PALCED IN BETWEEN VEHICLES (ROAD for paying out. When puller starts EACH tightening, pilot wire uses to uplift with STRATING PILOT WIRE CROSSING) high swing and speed. CHECKS: & GREEN FLAGS WITH WHISTILES MUST BEFORE TIGHTIENING OPERATION. AT LEAST TWO WITH SIGNAL BE MAN FLAG WALKI-TALKI POSTED AND SHALL ON ROAD CROSSINGS. PULLING OF CONDUCTORS BE ALL SITE ENGINEER SEVERE HIT INJURY
  12. 12. A) While conductor paying out is under IMPORTANT CHECK: INJURY TO progress one supervisor (must be capable The WORKMEN AND SIDE of making effective communication with PASSERS, ANIMALS & puller and tensioner operators and other VEHICLES (ROAD intermediate personnel’s positioned at road CROSSING) / power line crossings) must have to move B) FAILURE OF PILOT with head board. structures WIRE OR PILOT B) check out for free running of aerial headboard can stuck. WIRE CONNECTOR rollers and also obstruction free passing of Branches RESULTING IN HIT head board , mid-span joints ,pilot falling in the line of INJURY. connectors by deploying signalman’s at headboard every tower . hey may tasked with keeping vigil in between spans so as to keep unauthorized personnel’s away from particular phase corridor. C) Check SWL of pilot wire connector and its physical condition and also instruct operator (puller) slow down pulling when connector uses to enter in bull wheal of puller machine. MAKE UP & ROUGH SAGGING OF CONDUCTORS entire proposed section for paying out shall be checked for visual hindrances such trees, buildings & any other type of where of tress are more dangerous, and it must be cleared without taking any chance. SITE ENGINEER / GANG LEADER a)SEVERE HIT
  13. 13. Ensure the effective depth for deadment (depth DEADMENT not less than 6.0feet) and also condition of wood ANCHOR / FAILURE log(length not less than 6.0 feet and dia. 10- OF CAME ALONG 14inches)or steel beam of suitable section shall CLAMP. be ensured. IMPORTANT CHECK: 10.0-12.0 FEET 6.O’’ Use of 18mm or 20mm steel wire rope in good condition shall be used for holding conductors. ENSURE THE EFFECTIVE Check the condition of came along clamps& D- DEPTH shackles being used for holding conductors for NEALRY 6.0 FEET. following--- ENSURE A) Liner condition of came along clamp. ROPE OF DEADMENT THAT WIRE EMEREGS (FROM GROUND) AT LEAST 10.0 B) Availability of all bolts& nuts and packing –12.0 FEET AWAY FROM washers. TOP OF PIT. FOR THAT C) Availability of both side check nut. SLOPE CUTTING AT 45* D) Suitable capacity of D-shackle (min. 5.0 ton SHALL BE ENSURED TO AVOID DIECT best suited 10.0ton capacity) LOAD E) never replace the pin of D-shackle with any ANCHORE. other means. FINAL SAGGING OF CONDUCTORS CHECK FOR SAGGING ARRANGMENT AND TOOLS & TACKLES ON UPLIFT DEADMENT SITE ENGINEER/ GANGLEADER FAILURE OF
  14. 14. AND OF TOOLS TACKLES RESULTING IN CHECK POINTS IN FINAL SAGGING IMPORTANT CHECK: ARRANGMENT. Use articulated joint We must note final sagging is the most of capacity not less critical activity of stringing which involves application of very have load and failure of any kind can disastrous. Such as fall of towers injuries to workmen. 3.0 ton with 12.0 mm wire rope used in between four- sheave pulley arrangement to Before finalizing the tools and tackles we avoid or must give attention over sag chart and twist in wire rope. select the section that requires heaviest P.P loading and accordingly select tools and tied at both end of tackles for all sections. four GENERAL CONSEDRATION ACSR (QUAD) D/C LINE A) Check the condition of sag plate and condition of welding. in. thickness of sag plate shall be of 12mm. B) Use min. 15ton capacity kinking rope shall sheave shall be pulley used for to avoid its turning. The 12.0mm rope lead out wire coming from four sheave D-Shackle be pulley should be set routed connecting sag plate with four-sheave pulley through close type lifter arrangement. pulley positioned; B) Use good condition 12.0mm dia. Wire rope for A) Near tip of the making lifter arrangement with two four sheave pulley sets. Both four sheave pulley shall be separated a min. length 50.0-60.0M wire rope of 12.0mm dia. length of lifter arrangement should cross arm. & B) Near bottom rafter of cross arm with tower leg. be sufficient enough so as to ensure tightening A min. of 10.0 ton of conductor. capacity sag winch C)one set of lifter arrangement uses to lift two shall conductors giving load. in quad arrangement and one be used for Site engineer /gang leader FAILURE
  15. 15. Accordingly select the suitable capacity of four- Always sheave pulley block (SWL of min. 10.0Ton for loading sudden during final sagging operation. Check point for sag Equalizer pulley and four-sheave pulley shall be winch: connected directly with 15.o ton capacity D- A) Check the condition shackle. and suitability of bolts V-sling used for holding conductors shall of— A) 18.0mm wire rope for twin conductors being used for holding sag winch with tower leg. B) 22.0mm wire rope for quad conductors. B) proper working of Use twin came along clamps for holding single locking arrangement. conductor. Three bolt earth wire clamp or clamp used automatic shall for extra only be providing safety lock to wire rope after giving final winch. MARKING AND CONNECTING OF CONDUCTORS WITH HARDWARE FITTINGS CLIPPING ACTIVITY JHUMPERING AND SPACERING load from sag Site engineer /gang leader quad and 5.o ton for twin). avoid
  16. 16. Incorrect and may lead to failure of cross –arm from leg member and cross-arm rafter join position Correct sequence of looping wire rope from single sheave pulleys , in insulator hoisting.
  17. 17. COMMAN CAUSES OF ACCIDENTS IN THE WORK OF INSTALLATION OF CONDUCTORS IN T/L 1. General lack of awareness and commitment to safe working methods by workers, supervisors, & site Engineers. 2. Negligence in using appropriate personnel protective equipments at work places. 3. Lack of knowledge and experience in proper use of personnel protective equipments. 4. By passing / ignoring safety rules for reasons of misconceived convenience for faster Execution of work. 5. Use of an inappropriate / damaged tools and tackles. 6. Failure of tension bearing materials/ equipments. 7. Inadequate guying of towers or failure of tension bearing tools. 8. Improper or over tightening of conductors during sagging operations. 9. Lack of good communication and commuting facilities. 10. Lack of proper training and continuing education to workers, supervisors and Engineers in construction methods. 11. In adequate supervision of work by qualified and experienced personnel. 12. Lack of discipline in controlling non-compliance of safety regulations. 13. Exhaustion due to over working by workers. 14. Scattered working locations, difficult in having proper control over work locations. 15. Difficult terrains and natural topography
  18. 18. MEASURES AND PRECAUTIONS TO BE TAKEN IN WORK OF INSTALLTION OF CONDUCTORS IN T/L PREPARATORY WORKS 1. Preparation of towers – tower shall be complete in all regards before starting stringing operation. 2. Guying arrangement of towers shall be done as per given work procedure 3. Inspection and testing of tools and tackles ( follow checklist) 4. Inspection of personnel protective equipments for adequacy and workability. 5. Pre-task briefing to workmen and gang leaders before starting the job and fixing of accountability. 6. Information and caution to general public through caution boards and sign boards. 7. Identification of nearby hospital /medical center as a emergency preparedness. 8. Removal of tress and other visual obstructions in line corridor. 9. Identification of existence, source and listing power lines in section where the work is set out. 10. Arrangements for road or highways crossing coming in pathway of line corridor. 11. Providing temporary earth electrode for stringing equipments. 12. Adequate no. of First –Aid kit shall be made available at all work places. 13. Any restrictions on patter n of loading of towers shall be ascertained from designer.
  19. 19. 14. Ascertaining for restrictions on placement of pulleys and application of tension for hoisting and sagging operation. COURSE OF WORK 1. checking of all the towers immediately before commencement of insulator hoisting, for tightening punching, tack welding and availability of all members. 2. Positioning of pulleys for hoisting of insulators and other materials and equipment to be done correctly to avoid improper pull on the cross arms and towers. (Refer insulator hoisting Methodology) 2. Clear path for maneuvering tractors puling the hoisting slings for lifting material / Tensioning. 4. Availability of gang leader to co-ordinate pulling and lifting operation. 5. Proper counter weight anchors or log anchors to be installed for guying the towers, tension and puller equipments and for holding conductors under rough sag. 6. Turn buckles used for stay wires should be tightened periodically. 7. All workers working at height above 2.0M heights shall have to wear safety belt. 8. Effective and clear communication system shall be made available
  20. 20. METHODOLOGY OF STRINGING Stringing Methods & General Aspects Methods of stringing. There are basically two methods of stringing. These are i) Slack or Manual methods ii) Tension method i) Manual method: Using this method, the conductor is pulled along the ground by means of a pulling vehicle (normally tractor),or the drum is carried along the line on a vehicle and the conductor is deposited on the ground. The conductor drums are positioned on drum stands or jacks either placed on the ground or mounted on a transporting vehicle. These stands are designed to support the drum on an arbor, thus permitting it to turn as the conductor is pulled out. Usually, a braking device is provided to prevent overrunning and backlash. When the conductor is dragged past a supporting structure, pulling is stopped and the conductor is placed in travelers attached to the structure before proceeding to the next structure. ii) Tension Method: Using this method, the conductor is kept under tension during the stringing process. Normally, this Method is used to keep the conductor clear of the ground and obstacles, which might cause conductor Surface damage and clear of energized circuits. It requires the pulling of a light pilot line into the travelers, which in turn is used to pull in a heavier pulling line. The pulling line is then used to pull in the conductors from the drum stands using specially designed tensioners and
  21. 21. pullers. For lighter conductors, a lightweight pulling line may be used in place of the pilot line to directly pull in the conductor. STRINGING PROCEDURE The stringing procedure is broadly divided into the following steps. i) Paying out & stringing of earth wire. ii) Guying arrangement of tower iii) Insulator and aerial roller hoisting iv) Paying out of pilot wire iv) Paying out & stringing of conductor. v) Final sagging of earth wire & conductor. vi) Clipping and fixing of accessories. vi) Fixing of line spacers viii) Fixing of jumpers i) Paying out & stringing of earth wire: Normally stringing of earth wire is done manually since handling the earth wire is easy and it does not get damaged easily. First, earth wire rollers are provided on the earth peaks of all the suspension towers in the section. Before hoisting of earth wire rollers, it may be ensured that the rollers are free from friction. A lineman/ fitter may be kept on each tower to ensure free running of the rollers with a red & Green flag and whistle. At the starting end of a section, earth wire reel is mounted on roller jacks or horizontal turntable. The earth wire is pulled from tower to tower manually or by using a tractor. After reaching the next tower the earth wire is passed through the suspended earth wire
  22. 22. rollers with the help of a polypropylene rope and paying out is continued further. After one length of earth wire reel is exhausted, the second length of wire is paid out for the balance section. Mid span joint for earth wire is compressed on the ground joining the two lengths. Guying arrangement of tower Before commencement of stringing, the angle towers where the stringing is to be started have to be Provided with guy supports for all the three phases. The guys used generally are 20mm steel wire rope. The guys are attached to the tower at the tip of the cross arms and center of the bridge, to the strain plates with suitable D shackles. The guys are anchored in the ground at an angle of 45 Degrees or less from the horizon, attached to dead end anchors. For making dead end anchors in the Ground, pits of 1.5mx0.6m, for a depth of 1.5m can be dug. A set of steel beam and channels tied in the center with 16mm wire rope, is lowered and the pit is back filled while compacting. The guy wire is attached to the dead end anchor wire with the help of turnbuckles of 10 tonnes capacity. Alternately, instead of buried ground anchors, a dead weights of sag 5 to 10 tonnes can be placed on the ground and sag wire attached to them securely. After pulling up the slackness in the guy, it is tightened by the turnbuckle. Excessive tightening of the guy should be avoided. It is advisable to tighten the guy progressively at the time of rough sagging of the conductor.
  23. 23. Insulator and aerial roller hoisting Transportation of Insulators The required no. of insulators shall be transported to the tower locations with the wooden packing. The crates shall be opened at the tower location. The Insulator hoisting is done well in advance of Commencement of paying out operation. HOISTING: After opening of the crates, insulators shall be laid in series, on wooden planks below the suspension points. The insulators shall be cleaned with water and wiped dry with clean cloth free from grease and oil. Insulators shall be checked for any chipping or crack and shall be replaced with new one if found defective. The no. of insulators required for string shall be joined and `R' clips in the clevis shall be expanded to avoid slippage of the pin. The joints of all insulators should be checked and `R' clips should be expanded. The bottom insulator is joined to the moose aerial roller. The five wheels of the aerial rollers should be checked for free running. The neoprene rubber cushion on the outer rollers shall be checked for any cracks/wearing out and shall be changed if required. A single sheave pulley is fixed to the cross arm very near to the suspension hanger. A 20 mm polypropylene rope or 12mm wire rope is passed through the pulley and both the ends are brought to the ground. One end of the rope is firmly tied below the 3rd or 4th insulator. The complete string with aerial roller is lifted up by pulling the rope through a pulley attached to one of the tower legs by using tractor/manually After reaching the top the string is attached to the suspension hanger and string is released slowly to hang free.
  25. 25. Paying out of pilot wire In tension stringing, a pilot wire is used to pull the conductor. The pilot wire is initially laid through the center wheel of the aerial roller. A 22 mm dia pilot wire is generally used for pulling of quad moose ACSR conductor. The pilot wire can be laid length by length and joined with pilot wire connectors. At power line crossings, the pilot wire is laid from both sides and free ends are joined after obtaining the shutdown of the power line. Sound Scaffoldings shall be provided for P&T and road crossings before paying out of the pilot wire. A stand signalman shall be ensured with Red and green flag and also with walky-talky to ensure effective communication pilot wire pulling equipment (Tractor or Puller). Paying out & stringing of conductor. A) Position of tensioner and puller: The paying out of conductor is done generally between two tension towers. The puller machine can be Positioned behind the tension tower on one side and the tensioner in front of the tension tower on the other side. The entry of the pilot wire into the bull wheels of the puller machine and running out from tensioner machine should be as nearly horizontal as possible. Both the machines should be securely anchored with two dead end anchors in the ground and slackness is removed in the stay. The placement of drum jacks should be such that the lateral angle of conductor approach into the bull wheel through guide rollers is low enough to avoid rubbing on the sides and creating loosening of the outer strands and bird caging. The distance of the drums from the tensioner shall be at least 25 to 30 mtrs so as to distribute the effect of sliding of outer strands due to low back tension. The reel should be positioned so that it will rotate in the same direction as the bull wheels.
  26. 26. Paying out of conductor: For passing the conductor through the bull wheels of the tensioner, a 25 mm polypropylene rope is initially wound over each bull wheel pair in the same way as the conductor will pass during Running. The ropes are connected to the conductors. The conductor run shall be from the topside of the drum. The rope is pulled by starting the tensioner at low pay out tension to pass the conductor through bull wheels and are brought out through the guide rollers. The sub conductors are attached to the equalizer pulley/running board by means of wire mesh/end socks and swivel joints. The pilot wire is attached to the other end of the running board with swivel joint. At the puller site, the pilot wire is pulled to remove all slackness using the reel winder. The wire is passed through bull wheels of the puller and connected to the reel winder machine. The tensioner can be initially set for a tension of 2 to 2.5 tones. Caution should be made over the wireless hand set to all the Staff who are at middle points and to the tensioner operator that pulling is about to be started so that they can stay clear of pilot wire. The puller is started to draw up the pilot wire until the bull wheels of the tensioner start moving.ow paying out of Bundle conductors with tensioner and Puller. Care should be taken that the pilot wire does not get entangled in trees, scaffoldings, Aerial rollers etc. while going up during tensioning. This can be monitored by the staff who are posted in between the section and guiding the puller operator over the wireless sets. The pulling of the conductor may be done at a moderate speed while the running board is passing through the aerial rollers.The tension in the tensioner must be adjusted so that the conductors travel well over the ground. In long spans where conductor is likely to touch the ground, ground rollers may be placed so that the conductor can pass without any scratches. A running ground shall be connected to the conductor and pilot wire before paying out near the tensioner and puller which shall be earthed at the nearest tower. Platforms shall be erected with sturdy bellies, where roads, rivulets, channels, telecommunication or overhead power lines, railway lines, etc. have to be crossed during stringing Operations. It shall be seen that normal services are not interrupted or damage caused to property.
  27. 27. The back tension of the conductor behind the tensioner has to be maintained as per the requirement of the tensioner deployed. The back tension is adjusted by means of brakes provided on the drum jack. A running ground shall be connected to the conductor and pilot wire before paying out near the tensioner and puller which shall be earthed at the nearest tower. The speed of pulling of the conductor should be such that to achieve smooth operation. Slower speeds may cause significant swinging of the running blocks and insulator hardware assemblies. Higher speeds can create greater damage in case of malfunction. The tension applied during stringing generally is about half the sagging tension. When long lengths of conductors are strung, the tension at the puller may be higher than that at tensioner due to the length of conductor strung, number and performance of travellers, differences in elevation of supporting structures etc. Jointing of conductor: Just before one length of the conductor paying out is completed another drum has to be deployed in advance beside the first drum. The paying out has to be stopped by braking the tensioner and stopping the puller simultaneously. The paid out conductor of first drum is held with bolted comealong clamps at a distance of 40 to 50 mtrs from the tensioner. The come- along clamps are attached to the ground anchor stays. The conductor of the first drum is held and the free end is cut. The free end of the second drum is also prepared. The two ends are joined with a wire mesh mid span socks. The paying out is again started by releasing the come along clamps until the mid span socks emerges outside the tensioner and pulling is stopped. After anchoring, the conductor is slowly drawn out from the two end socks. The mid span socks is removed and mid span compression joint is made. After making mid span joint, the joint is covered with joint protector sleeves which is designed to pass over the aerial roller grooves without damaging the mid span compression joint. The paying out is continued until the conductor reaches the puller end in sufficient length to be connected to the
  28. 28. Tension hardware.
  29. 29. Rough sagging of conductor Before final sagging the conductor, it is rough sagged to a tension slightly less than the final Tension. Since final sagging is done from one end of the section, the conductor is initially attached to the double tension string assembly on the other end. For doing rough sagging, initially the double tension string assembly is assembled with insulators and hardware and hoisted to the cross arms/bridge as done in the case of suspension towers. The dead end cones are compressed on both the sub conductor ends. The conductor is held by come along clamps at a distance of 5 to 6 mtrs from the dead end cones and with the help of a pulley connected to a ground anchor, the conductor is pulled to slacken the free end of conductor (sufficient length to be attached to the hoisted insulator string assembly).By holding the conductor with pulley, the dead end cones are attached to the tension string. The pulley is slowly released and the conductor will haul-up itself to the top. The come along clamps and pulley etc. are removed. Final sagging of conductor The sagging of the conductor shall be done using sagging winches. After being rough sagged the conductor shall not be allowed to hang in the stringing blocks for more than 96 hours before being Pulled to the specified sag. The tensioning and sagging shall be done in accordance with the approved stringing charts before the conductors are finally attached to the towers through the insulator strings. Only after the conductor is rough sagged on the adjacent section, final sagging can be done in the preceding section to avoid overloading of towers. For doing the sagging operation, a span has to be selected in the section to fix the sag board and check the sag. In the event of using sag tension charts showing sags in each of the actual spans and tension in each section, usual practice is to place the sag boards in the longest span of the section, and in a span where the difference of elevation in the two suspension points is minimum. The tension insulator strings are hoisted with all hardware on the tower. The conductors are held by come-along clamps and attached to Separate four sheave pulleys at sufficient distance of say 40
  30. 30. to 50 mtrs depending upon rough sag condition and height of the tower. The other ends of the foursheave pulleys are connected to the line side yoke plate of the double tension string. The pulling wires of the four-sheave pulley are passed through a set of single sheave pulleys along the body of the tower to the ground level. The initial pulling is done with the help of tractor/truck. Then the Pulling ropes are attached to hand winches mounted on the legs of the tower or power winches duly Anchored. Wooden cross bars are tied to the body of the four sheave pulley and held by ropes in a Horizontal position to avoid over turning of the four-sheave pulley and twisting of the pulling wires. The conductor is brought into final sag position with the help of winches and the sag is checked by sighting far end sag board from behind the near end sag thread by matching elevation tangent of the conductor curve. Sighting should be done keeping sufficient distance from the sag line to avoid parallax error. After reaching the final sag, the free end of the conductor is picked up and pulled by rope and pulley attachment along the line of the string. The conductor is marked at the point where cutting is to be done and dead-end cone is to be pressed. The free ends of the conductors are brought down and cut near the marking and dead end cones are pressed. The four-sheave pulley is slightly tightened to facilitate attaching the dead end cone to the tension assembly. After fixing, the four-sheave pulley is slowly released, brought down and all clamps and pulleys are removed. Clipping of conductors: The clipping of the conductor follows sagging operation. This entails removing the conductors from The rollers and placing them in suspension clamps attached to the insulator string. Before taking Up clipping operation, the conductor is earthed properly on suspension towers. The conductors are Held with hooks at 2 mtrs away from the aerial roller on both sides. A wire rope is connected to Both the hooks passed through a pulley positioned on the cross arm tip in series with a pulllift/ratchet lever hoist/four or two-sheave pulley. The center of the aerial roller is marked on the conductor. The conductor is raised by about 75 to 100 mm and the aerial roller is removed and
  31. 31. lowered by rope and pulley. The suspension clamp and armoured rods are fixed with neoprene rubber cushions centered over the marking. The suspension clamp is placed over the armored rods and clamped with U bolts. The suspension clamp is connected to the string and the lifting device is Released. The insulator string will hang freely with the conductors suspended in the clamps. The Verticality of the string may be checked with plumb bob. Care should be taken to prevent any damage to the conductor while being lifted by hooks. Gunny bags or rubber pads may be used around the conductor to prevent damage to the outer strands. Fixing of line spacers : Following the clipping operations for bundled conductor lines, spacers are usually installed. This is done by placing personnel on the conductors with the use of a conductor cycle normally known as spacer-cycle to ride from structure to structure. Depending on the length of line to be spaced and the equipment available, cycles may be hand powered or diesel powered. Care must be exercised to ensure that the concentrated load of the man, car and equipment does not increase the sag sufficiently to cause hazards by obstructions (spacers, repair sleeves, mid span joints etc.) over which the cycle will pass. The installation of the spacers on the conductor varies with span length, the type and manufacture of the spacer and is normally done in accordance with the manufacturer's recommendations duly approved. The spacer cycle is hoisted on the bundle at one tension end. In case of engine-powered cycles, the spacer cycle is normally provided with travel meter, with the help of which the spacers are fixed at required distances as per the placement chart. In case of hand-powered cycles, the personnel pulling the cycle with rope measure the distances on ground and placement is done on the top. A number of models of spacers are being manufactured and the method of installation varies with the design of the spacers. After reaching the next suspension tower, the cycle is transferred to the next span by crossing the suspension clamp with the help of crossing ropes provided in the cycle. In case of spans crossing HT/LT lines, care should be taken while drawing the spacer cycle with rope. Safe electrical clearance should be
  32. 32. maintained to the spacer cycle and rope. For crossing the lines, the rope shall be drawn up to the cycle, and brought down after crossing the line, keeping sufficient clearance from the line. The person on the cycle can travel himself to cross over the section above the power line. Installation of dampers: Vibration dampers/spacer dampers are normally placed on the conductors immediately following clipping to prevent any possible damage because of vibrations to the conductors, which at critical tensions and wind conditions can occur in a matter of hours. Jumpering The jumpers at the section/angle towers shall be formed to parabolic shape to ensure minimum clearance requirements. Pilot suspension insulator string shall be used if found necessary (Generally where angle of deviation is more than 45 degrees), to restrict the jumper swings to the design values at both middle and outer phases. Clearance between the conductors and ground, jumpers and the tower steel work shall be checked during erection and before commissioning the line. While jumpering is made, a local earthing should be made to avoid any static discharge that might occur due to the voltage induced on the line by existing power lines in the vicinity. Care should be taken to leave jumpers for one angle tower in a continuous stretch of 25 to 30 kms, so as to prevent transmission of electric shock. These left out jumpering can be taken up during final inspections. The individual sections jumpered shall be kept earthed and earth shall be removed only before commissioning. The jumpers in general are 10 to 15 mtrs in length. Hence left over bits of conductor shall be used for jumpering. For installation of jumpers, the distance between the jumper pads of dead end cones is measured by passing a rope in the shape of a jumper and by checking vertical clearance from the cross arm end. Conductor is cut after making adjustment in length for the jumper cone dimension. The inner and outer conductor of the bundled jumper are of different lengths, which shall be measured separately. This will ensure a horizontal plane of the jumper
  33. 33. bundle when installed. After cutting the conductor, jumper cone is pressed using hydraulic compressor. The conductors are laid out on the ground parallelly and spacers are fixed as per the fixing instructions. The jumper is hauled up from both ends of the tension clamps and jumper cone is attached to the connector of the dead end cone. Clearance to the tower body shall be checked as per the drawing.
  35. 35. SAFETY ASPECTS OF TOWER ERECTION IN TRANSMISSION LINE METHODS OF ERECTION There are THREE main methods of erection of steel transmission towers, which are described, as below i. Built-up method or piecemeal method. ii. Section method iii. Ground assembly method.
  36. 36. Built up method This method is most commonly used in this country for the erection of 66 KV, 132 KV, 220 KV and 400 KV Transmission Line Towers due to the following advantages. i. Tower materials can be supplied to site in knocked down condition which facilitate easier and cheaper transportation. ii. It does not require any heavy machinery such as cranes etc. iii. Tower erection activity can be done in any kind of terrain and mostly through out the year. iv. Availability of workmen at cheap rates.This method consists of erecting the towers, member by member. The tower members are kept on ground serially according to erection sequence to avoid search or time loss. The erection progresses from the bottom upwards, the four main corner leg members of the first section of the tower are first erected and guyed off. Sometimes more than continuous leg sections of each corner leg are bolted together at the ground and erected.The cross braces of the first section which are already assembled on the ground are raised one by one as a unit and bolted to the already erected corner leg angles. First section of the tower thus built and horizontal struts (bet members) if any, are bolted in position. For assembling the second section of the towers,two gin poles are placed one each on the top of the diagonally opposite corner legs. These two poles are used for raising parts of second section. The leg members and braces of this section are then hoisted and assembled. The gin poles are then shifted to the corner leg members on the top of second section to raise the parts of third section of the tower in position for assembly. The gin pole is thus moved up as the tower grows. This process is continued till the complete tower is erected.Cross-arm members are assembled on the ground and raised up and fixed to the main body of the tower. For heavier towers, a small boom is rigged on one of the tower legs for hoisting purposes. The members/sections Are hoisted either manually or by winch machines operated from the ground. For smaller base towers/vertical configuration towers, one gin pole is used instead of two gin poles. In order to maintain speed and efficiency, a small assembly party goes ahead of the main erection gang and its purpose is to sort out the tower
  37. 37. members, keeping the members in correct position on the ground and assembling the panels on the ground which can be erected as a complete unit. Sketches indicating different steps of erection by built up method are shown at Figure 4.1 to Figure 4.7. Guying arrangement Guying arrangements are to be done at waist level/bottom cross-arm level as well as in the girder level/top cross-arm level depending on SC/DC towers and it is to be installed at 450 from vertical. The deadments for guying arrangements are to be properly made. A sample of deadments drawing is enclosed at Figure 4.8 for reference. Guying should be steel wire or polypropylene rope depending Upon requirements. Nominal tension is to be given in guying wire/rope for holding the tower in position.