Method Statement for Transmission Line Conductor Installation

What is the Method Statement for Transmission Line Conductor Installation?

The Method Statement for Transmission Line Conductor Installation involves a systematic approach beginning with a project overview, emphasizing safety precautions, and detailing steps for execution. It includes the installation of towers or structures, setup of stringing equipment, inspection of conductor reels, and a defined stringing sequence with attention to sag and tension considerations.

The method outlines procedures for conductor splicing, termination, and testing, ensuring compliance with industry standards and quality control measures. Environmental considerations and documentation are integrated throughout the process. The method statement concludes with procedures for project completion, including demobilization, site cleanup, and final inspection to confirm adherence to project specifications. This comprehensive framework serves as a guide for the effective and safe installation of conductors in transmission lines.

Course of Work in Conductors Installation

Insulator Hoisting Preparation

1. Conduct a thorough check of all towers just before starting insulator hoisting. Ensure tightness, punching, tack welding, and member availability.

2. Position pulleys accurately for hoisting insulators, materials, and equipment to prevent improper pull on cross arms and towers.

3. Maintain a clear path for maneuvering tractors pulling the hoisting slings, facilitating material lifting and tensioning.

4. Ensure the availability of a gang leader to coordinate pulling and lifting operations.

5. Install proper counterweight anchors or log anchors for guying towers, tensioning and pulling equipment, and for holding conductors under rough sag.

6. Periodically tighten turnbuckles used for stay wires.

7. All workers operating at heights above 2.0 meters must wear safety belts.

8. Implement an effective and clear communication system.

Methodology of Stringing

Methods of Stringing

There exist essentially two approaches to stringing.

a) Manual method

In this technique, the conductor is drawn across the ground with the aid of a pulling vehicle, usually a tractor, or the drum is transported along the line on a vehicle, depositing the conductor on the ground. Conductor drums are positioned on drum stands or jacks, either on the ground or mounted on a transporting vehicle.

These stands are designed to support the drum on an arbor, allowing it to turn as the conductor is pulled out. Typically, a braking device is included to prevent overrunning and backlash. When the conductor moves past a supporting structure, pulling halts, and the conductor is placed in travelers attached to the structure before advancing to the next one.

b) Tension Method

In this approach, the conductor is maintained under tension throughout the stringing process. Commonly, this method is employed to keep the conductor above the ground and away from obstacles that could cause surface damage or interfere with energized circuits. It involves pulling a light pilot line into the travelers, which is then used to draw in a heavier pulling line.

The pulling line is then utilized to pull in the conductors from the drum stands using specially designed tensioners and pullers. For lighter conductors, a lightweight pulling line may be substituted for the pilot line to directly pull in the conductor.

Stringing Procedure

The stringing process involves several key steps:

• Stringing of Earth Wire : Manual stringing of the earth wire is the standard practice due to its easy handling and durability. Earth wire rollers are placed on the suspension towers, facilitating the process.
• Paying Out & Stringing of Earth Wire : To ensure smooth operation, earth wire rollers must be free from friction. Linemen/fitters are stationed on each tower with flags and whistles to monitor roller movement. The earth wire is pulled manually or by a tractor, passing through rollers at each tower.
• Hoisting of Earth Wire Rollers : Before initiating the stringing process, guy supports are installed on angle towers where stringing begins. Steel wire ropes, typically 20mm, are attached to tower points and strain plates. Dead end anchors are established at a 45-degree angle or less from the horizon.
• Insulator and Aerial Roller Hoisting : A 1.5mx0.6m pit, 1.5m deep, is dug for dead end anchors. A steel beam and channels, secured with 16mm wire rope, are lowered into the pit, which is then backfilled while compacting. Turnbuckles of 10 tons capacity connect the guy wire to the dead end anchor wire.
• Paying Out of Pilot Wire : To avoid excessive tightening, the guy wire is progressively tightened during rough sagging of the conductor. Dead weights, sagging 5 to 10 tons, can also be employed instead of buried ground anchors.
• Paying Out & Stringing of Conductor : The conductor is strung by paying it out manually or with the help of machinery. Care is taken to avoid damage during the process. The final sagging of the earth wire and conductor is crucial for ensuring the desired tension and alignment.
• Final Sagging of Earth Wire & Conductor : Mid-span joints for the earth wire are compressed on the ground, connecting the lengths and ensuring continuity. It is a critical step in maintaining the structural integrity of the transmission line.
• Clipping and Fixing of Accessories : Once the conductor is in place, accessories such as clamps and spacers are fixed to ensure the stability and proper functioning of the transmission line.
• Fixing of Line Spacers : Line spacers are fixed at appropriate intervals to maintain the separation between conductors and prevent any unwanted contact or interference.
• Fixing of Jumpers : Jumpers are installed to establish electrical continuity between different sections of the transmission line, ensuring a reliable flow of electricity.

Insulator and Aerial Roller Hoisting Procedure

Transportation of Insulators

The necessary quantity of insulators will be conveyed to the designated tower locations, securely packed in wooden crates. Upon arrival, the crates will be unsealed at the tower site.

Insulator Hoisting Preparation

To initiate the hoisting process, insulators will be arranged in a series on wooden planks beneath the suspension points, following the opening of crates. Prior to hoisting, each insulator will undergo a thorough cleaning with water and a dry wipe, ensuring the absence of grease or oil.

Inspection for any chipping or cracks is imperative, and any defective insulator will be promptly replaced with a new one. For the string, the required number of insulators will be connected, and ‘R’ clips in the clevis will be expanded to prevent pin slippage.

All insulator joints will be scrutinized, and ‘R’ clips will be expanded accordingly. The bottom insulator will be affixed to the moose aerial roller, with a meticulous check of the five wheels for smooth rotation.

Verification of the neoprene rubber cushion on the outer rollers for cracks or wear is essential, and replacement will be carried out if deemed necessary.

Hoisting Process

A single-sheave pulley will be securely attached to the cross arm near the suspension hanger. A 20 mm polypropylene rope or a 12 mm wire rope will be threaded through the pulley, and both ends will be extended to the ground.

The rope’s one end will be firmly fastened below the 3rd or 4th insulator. Using either a tractor or manual effort, the entire string with the aerial roller will be lifted by pulling the rope through a pulley connected to one of the tower legs.

Upon reaching the top, the string will be affixed to the suspension hanger, and the string will be gradually released to hang freely.

Insulator Hoisting

Pay out of the pilot wire:

During tension stringing, a pilot wire is utilized to draw the conductor. Initially, the pilot wire is threaded through the central wheel of the aerial roller. Generally, a 22 mm diameter pilot wire is employed for pulling the quad moose ACSR conductor. The pilot wire can be laid in sections and connected using pilot wire connectors. When crossing power lines, the pilot wire is set from both sides and later joined after the power line shutdown. For P&T and road crossings, sturdy scaffoldings must be in place before paying out the pilot wire.

A designated signalman should have a red and green flag, along with a walky-talky, to ensure effective communication with the equipment used for pulling the pilot wire (such as a tractor or puller). The process involves paying out and stringing the conductor.

In this process:

The positioning of the tensioner and puller is crucial. Conductor payout usually occurs between two tension towers. The puller machine can be placed behind one side of the tension tower, while the tensioner sits in front of the other. The pilot wire should enter the puller machine’s bull wheels and exit from the tensioner machine as horizontally as possible.

Both machines need firm anchoring using two dead end anchors in the ground, and any slackness in the stay should be eliminated. The placement of drum jacks must allow for a low lateral angle of conductor approach into the bull wheel through guide rollers to prevent rubbing against the sides, which could cause loosening of the outer strands or birdcaging.

The distance of the drums from the tensioner should be between 25 to 30 meters to distribute the effect of sliding outer strands due to low back tension. The reel’s position should ensure it rotates in the same direction as the bull wheels.

Paying out of Conductor

To thread the conductor through the bull wheels of the tensioner, a 25 mm polypropylene rope is initially wound around each bull wheel pair in the same manner as the conductor’s path during running. These ropes are then connected to the conductors. The conductor run should start from the topside of the drum. Initiate the tensioner at a low payout tension to pull the rope and guide the conductor through the bull wheels, bringing it out through the guide rollers.

The sub conductors are affixed to the equalizer pulley/running board using wire mesh/end socks and swivel joints. The pilot wire is attached to the opposite end of the running board with a swivel joint. At the puller site, pull the pilot wire to eliminate all slackness using the reel winder. Pass the wire through the bull wheels of the puller and connect it to the reel winder machine.

Set the tensioner initially to a tension of 2 to 2.5 tons. Exercise caution through the wireless handset to alert staff at middle points and the tensioner operator that the pulling is about to commence, ensuring they stay clear of the pilot wire. Start the puller to draw up the pilot wire until the bull wheels of the tensioner begin to move. Now, proceed with paying out bundle conductors using the tensioner and puller.

Ensure that the pilot wire does not become entangled in trees, scaffoldings, aerial rollers, etc., while ascending during tensioning. Staff positioned between sections should monitor and guide the puller operator through wireless sets. Pull the conductor at a moderate speed while the running board passes through the aerial rollers.

Adjust the tension in the tensioner to ensure the conductors travel smoothly over the ground. In long spans where the conductor may touch the ground, place ground rollers to facilitate passage without scratches. Connect a running ground to the conductor and pilot wire before paying out near the tensioner and puller, grounding it at the nearest tower.

Construct platforms with sturdy structures at locations where roads, rivulets, channels, telecommunication or overhead power lines, railway lines, etc., need to be crossed during stringing operations. Ensure that normal services are not interrupted, and no damage is caused to property.

The tensioner’s back tension should align with the tensioner’s requirements. To adjust the back tension, use the brakes on the drum jack. Connect a running ground to the conductor and pilot wire before paying out near the tensioner and puller, ensuring it is grounded at the nearest tower. Maintain a pulling speed that ensures smooth operation.

Slower speeds may cause significant swinging of the running blocks and insulator hardware assemblies, while higher speeds can lead to greater damage in case of a malfunction. The applied tension during stringing is typically around half the sagging tension. For long conductor lengths, the puller’s tension may be higher than the tensioner’s due to various factors such as conductor length, traveler performance, and elevation differences in supporting structures.

When joining conductors, deploy another drum beside the first drum just before completing the payout of one conductor length. Halt the payout by simultaneously braking the tensioner and stopping the puller. Secure the paid-out conductor from the first drum with bolted come-along clamps, maintaining a distance of 40 to 50 meters from the tensioner. These clamps should be attached to the ground anchor stays.

Cut the free end of the first drum’s conductor and prepare the free end of the second drum. Join the two ends with a wire mesh mid-span sock. Resume the payout by releasing the come-along clamps until the mid-span sock emerges outside the tensioner, and then stop the pulling. After anchoring, slowly draw out the conductor from the two end socks.

Remove the mid-span sock and create a mid-span compression joint. Cover the joint with joint protector sleeves designed to pass over the aerial roller grooves without damaging the mid-span compression joint. Continue the payout until the conductor reaches the puller end with a sufficient length for connection to the tension hardware.

Rough Sagging of Conductor

Before the final sagging of the conductor, it undergoes a preliminary sagging process, where the tension is slightly less than the ultimate tension. This preliminary sagging is executed from one end of the section, with the conductor initially attached to a double tension string assembly on the opposite end.

To perform rough sagging, the double tension string assembly is first assembled with insulators and hardware, lifted to the cross arms/bridge similar to suspension towers. Dead end cones are compressed on both sub-conductor ends. The conductor is secured by come-along clamps about 5 to 6 meters from the dead end cones.

Using a pulley connected to a ground anchor, the conductor is pulled to slacken the free end, allowing it to be attached to the hoisted insulator string assembly. The dead end cones are attached to the tension string by holding the conductor with a pulley.

The pulley is gradually released, allowing the conductor to haul itself to the top. Afterward, come-along clamps and pulley are removed.

Final Sagging of Conductor

The sagging of the conductor is carried out using sagging winches. Once rough sagging is completed, the conductor should not hang in the stringing blocks for more than 96 hours before being pulled to the specified sag. Tensioning and sagging adhere to approved stringing charts before attaching conductors to the towers through insulator strings.

Final sagging is only done in the preceding section after rough sagging the conductor on the adjacent section to prevent tower overloading. The sagging operation involves selecting a span in the section to fix the sag board and check the sag.

Tension insulator strings are hoisted with all hardware on the tower. Conductors are held by come-along clamps and attached to separate four-sheave pulleys at a distance of 40 to 50 meters. The conductor is brought into the final sag position using winches, and sag is verified by sighting the far-end sag board.

After reaching the final sag, the free end of the conductor is marked for cutting and attaching the dead-end cone. The four-sheave pulley is then released, brought down, and all clamps and pulleys are removed.

Clipping of Conductors

Following sagging operations, the clipping of conductors involves removing them from rollers and placing them in suspension clamps attached to the insulator string. Before clipping, the conductor is properly earthed on suspension towers. Conductors are held with hooks 2 meters away from the aerial roller on both sides. A wire rope connected to both hooks is passed through a pulley on the cross arm tip.

The conductor is raised, and the aerial roller is removed. Suspension clamps and armored rods are fixed with neoprene rubber cushions. The suspension clamp is connected to the string, and the lifting device is released. The insulator string hangs freely with the conductors suspended in the clamps. The verticality of the string is checked with a plumb bob. Care is taken to prevent damage to the conductor during lifting by using gunny bags or rubber pads.

Fixing of Line Spacers

After clipping operations for bundled conductor lines, spacers are installed. Personnel on the conductors, using a spacer-cycle, ride from structure to structure. The spacer cycle is hoisted on the bundle at one tension end. Depending on the length of the line to be spaced, cycles may be hand-powered or diesel-powered.

Care is taken to avoid hazards by ensuring the concentrated load of the man, car, and equipment does not increase the sag. The installation of spacers is done in accordance with the manufacturer’s recommendations. 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.

Installation of Dampers

Vibration dampers / spacer dampers are placed on the conductors immediately following clipping to prevent possible damage due to vibrations. The installation of dampers is crucial to counteract vibrations that can occur at critical tensions and wind conditions.

Jumpering

The jumpers at the section/angle towers are formed to a parabolic shape to ensure minimum clearance requirements. Pilot suspension insulator strings are used if necessary to restrict jumper swings to design values. Clearance between conductors and ground, jumpers, and tower steelwork is checked during erection and before commissioning the line.

Local earthing is made during jumpering to avoid static discharge induced by existing power lines. Jumpers are left for one angle tower in a continuous stretch to prevent electric shock transmission. Jumper sections are kept earthed and earth is removed only before commissioning. The individual jumper sections are 10 to 15 meters in length, using leftover conductor bits for installation.

Stringing Safety Check List

Safety Aspects of Tower Erection in Transmission Line Methods of Erection

There are three main methods of erecting steel transmission towers, described as follows:

1. Built-up method or piecemeal method.
2. Section method.
3. Ground assembly method.

Built Up Method

This approach, known as the built-up method, finds widespread application in this region for constructing Transmission Line Towers of 66 KV, 132 KV, 220 KV, and 400 KV.

Its popularity is attributed to several advantages:

• Tower materials can be supplied in a knocked-down state, easing and reducing transportation costs.
• Heavy machinery like cranes is unnecessary.
• Tower erection is feasible across various terrains and throughout the year.
• Availability of affordable labor.

This method involves the step-by-step assembly of tower components. The tower members are sequentially arranged on the ground based on the erection sequence to minimize search or time loss. The erection begins from the bottom, with the first section’s four main corner leg members being initially erected and guyed off. In some cases, more than continuous leg sections are bolted together on the ground and then erected.

The cross braces of the first section, pre-assembled on the ground, are raised one by one and bolted to the erected corner leg angles. The first tower section is built, and horizontal struts (bet members), if present, are bolted in place. For the assembly of the second section, two gin poles are positioned on the diagonally opposite corner legs.

These poles are utilized to raise parts of the second section, followed by hoisting and assembly of leg members and braces. The gin poles are then relocated to the corner leg members at the top of the second section for raising the parts of the third section. This process continues until the entire tower is erected.

Cross-arm members are assembled on the ground, lifted, and affixed to the main body of the tower. In larger towers, a small boom on one of the tower legs aids in hoisting. The members or sections are hoisted manually or using winch machines from the ground. For smaller base or vertical configuration towers, a single gin pole suffices instead of two.

To maintain efficiency, a small assembly team precedes the main erection group, organizing tower members on the ground, ensuring correct positioning, and assembling panels that can be erected as complete units. Sketches depicting various steps of the built-up method are provided.

Guys in Place

Concerning guying arrangements, these are implemented at waist level or bottom cross-arm level and girder level or top cross-arm level, depending on whether it is an SC/DC tower. The arrangement should be installed at a 450-degree angle from vertical, and appropriate deadments for guying arrangements must be established. A sample of deadments is provided.

Guying materials can be either steel wire or polypropylene rope, depending on specific requirements. Nominal tension is applied to the guying wire or rope to secure the tower in position.

Common Causes of Accidents in the Installation of Conductors in T/L

1. Widespread lack of awareness and dedication to safe working methods among workers, supervisors, and site engineers.
2. Neglect in the utilization of appropriate personal protective equipment at job sites.
3. Insufficient knowledge and experience in the correct utilization of personal protective equipment.
4. Bypassing or ignoring safety regulations for the sake of misguided convenience, aiming for faster execution of work.
5. Deployment of unsuitable or damaged tools and tackles.
6. Failure of tension-bearing materials and equipment.
7. Insufficient guying of towers or the breakdown of tension-bearing tools.
8. Improper or excessively tight fastening of conductors during sagging operations.
9. Lack of effective communication and commuting facilities.
10. Deficiency in proper training and ongoing education for workers, supervisors, and engineers in construction methods.
11. Inadequate supervision of work by qualified and experienced personnel.
12. Absence of discipline in controlling non-compliance with safety regulations.
13. Fatigue caused by overworking among laborers.
14. Scattered work locations, posing difficulties in maintaining proper control over work areas.
15. Challenging terrains and natural topography.

Measures and Precautions in Installation of Conductors

Prior to commencing the stringing operation, ensure the tower is fully prepared in all aspects.

Follow the prescribed work procedure for guying arrangement of towers.

Inspect and test tools and tackles using the provided checklist.

Check the adequacy and workability of personal protective equipment through a thorough inspection.

Conduct a pre-task briefing for workmen and gang leaders, emphasizing accountability.

Use caution boards and sign boards to provide information and warnings to the general public.

Identify the nearest hospital/medical center for emergency preparedness.

Remove trees and other visual obstructions from the line corridor.

Identify and list power lines in the section where the work is to be carried out.

Make arrangements for road or highway crossings within the line corridor.

Set up temporary earth electrodes for stringing equipment.

Ensure an adequate number of First-Aid kits are available at all work sites.

Ascertain any restrictions on the loading pattern of towers from the designer.

Written by:

Jose S. Villegas is a seasoned professional and civil engineer in the construction industry with over 24 years of experience. He has worked on various construction projects ranging from small to large-scale projects. He has a deep understanding of the construction process, from quality to implementation and completion.