This module will teach you on how to learn different equipment and their application to proper stringing techniques. Upon completion of this module you will be able to distinguish between and have a general understanding of Conventional and Tension Stringing methods.
Over the years, different equipment for stringing operations has been developed for the line trade. The original stringing methods seem quite crude in today's modern standards evolving from a team of horses and the crew pulling conductors to the high tech work methods of tension stringing. The ever increasing presence of hazards and obstacles has made it necessary to develop these methods in order to avoid unnecessary interference during stringing operations.
Slack stringing, also referred to as Conventional Stringing, has been the traditional method of low voltage stringing. It can be carried out safely in the vicinity of live lines provided proper precautions are taken. Under certain conditions, however, it becomes necessary to Tension String in the new circuit Similarities exist in setting up the work sites and all associated work practices in order to complete the task safely.
Before you move on in this module a definition of the two methods of stringing must be understood.
Tension stringing is the procedure for stringing conductor where there is positive and continuous control of conductor sag. This method is capable of moving conductors in both directions, ahead or backwards, utilizing a pulling machine and a tension machine(s).
Note: A bull wheel or capstan hoist and brake on a reel trailer or reel stand does not constitute tension-stringing equipment.
Certain criteria must be met to execute the work safely. These criteria are similar in conventional stringing as well as tension stringing. Deviation from these work practices may create a hazardous work situation, which may ultimately lead to an accident.
Job planning is of the utmost importance prior to the beginning of the job. Careful planning and a site visit before stringing the new conductors is essential, as each new stringing job brings with it new problems and different situations. Those people directly responsible for the job should be involved to ensure a quality job plan is in place and all steps and requirements are covered and met
During a site visit the following items should be considered:
- Condition of existing poles, hardware and conductor
- Height of existing line
- Existing guying and anchors
- Length of spans, angles and hills
- Open and/or isolation points (temporary and permanent)
- Public safety
- Vehicle accessibility and site selection for equipment
- Vicinity of live circuits
Inspect the pole line for correct framing and guying. Check the existing pole line anchor rods for their condition and make certain that the anchors and guy steel are adequate for the new conductor tensions. Make sure that the existing framing and hardware is in good condition.
The vicinity of live circuits must be checked when stringing operations are to be carried out Specific precautions must be taken if adequate clearances cannot be maintained and the circuit must be covered up or isolated and de-energized. When conductors are being strung in the vicinity of energized circuits, the most important aspect of the job is to ensure proper grounding procedures are followed. These grounding procedures will be discussed later in this module.
Lockout and Tagout Procedures must be adhered to during any stringing operations in the proximity of energized apparatus. The possibility of an inadvertent contact with live electrical devices must be minimized with the use of "R-Switch" protection combined with approved work practices. Any existing isolated lines in proximity to the stringing operation if possible should be de-energized and tagged in accordance with the Lockout and Tagout Procedures.
Work Area Protection (Public) must be established in accordance with local bylaws and the Highway Traffic Control Laws. Site preparation for stringing operations is critical in maintaining extra barriers.
Work Area Protection (Utility Personnel) is critical in establishing a safe work environment during any stringing operation. Considerable emphasis is placed on isolation techniques and grounding procedures when using hydraulically driven tension machines.
Select sites for reel stands and equipment in advance, bearing in mind access for vehicles, hard level ground, and property availability. The reel stands should be set back from the first pole a minimum distance of three times the height of the first set of travelers.
Road, railway and water crossings require extra planning due to approval from various authorities. Railway crossings require a written request and permission a few days in advance before the conductors may be strung over the crossing. Road or highway crossings require cooperation with the municipal or provincial police for traffic control.
Rider poles may be installed adjacent to railway; road or water crossings when stringing operations seriously disrupt the flow of traffic. This may not be a requirement when tension stringing.
Various equipment used for conventional stringing operations will also be used for tension stringing applications. They will include pulling ropes, running boards, pulling grips (Kellem), swivels and appropriate rollers.
Pulling grips or Kellem grips are a fast and easy method of joining pulling ropes to conductors. They are only slightly larger than the conductor and allow smooth passage of the connections of the pulling line and conductor through the traveler. They may be used in single conductor pull applications or multi-conductor stringing operations.
The Kellem grip presently recommended for line work is the "Multiple Strength Pulling Grip," (see Figure 1) which is easily identified by its construction of a single weave section at the open end of the grip, double weave in the center portion and triple weave at the metal shoulder of the grips. The metal shoulders protect the end of the conductor and equalize strand loading.
Figure 1
Check the Kellem grips on the pulling rope or bull rope as it is being constantly pulled backwards through rollers. A "hollow braid" pulling rope may require a length of wire or guy steel as a core in the section where the grip fastens, to preventing the collapse of the rope.
Punch-Lock Bands shall be installed on all open ends of Kellem grips 1" from the end. This is to prevent the edges of the grip from catching on the edges of the roller thereby pulling it off the conductor if it must be moved in the reverse direction. It is also recommended that the front end of the grip be taped to prevent the conductor from protruding through the aluminum shoulders on the grip. Figures 2a - d indicate the correct procedures to install Punch-Lock bands.
Figure 2a Figure 2b
Flgure2c Figure 2d
Swivels are necessary to join the Kellem grips on the pulling line and the conductor preventing the buildup of torsional tensions. When pulling conductor, the torque builds up rapidly as a result of the pull on the stranded rope by the pulling equipment. Swivels are necessary at all running board connections to aid in the prevention of the running board rotating and tangling the conductor. See Figure 3. During conventional stringing swivels may not always be required but under tension conditions it is highly recommended.
Figure 3
Finger lines are installed through the rollers with both ends tied off at the base of the pole. It is usually 1/4" to 3/8" rope used to pull in the pilot line.
Pilot lines are used to pull in the larger pulling rope for tension stringing operations. It is usually 3/8" to 5/8" in diameter. Pilot lines are often used during conventional stringing attaching it to the conductor and pulling it through the stringing block or traveler.
When selecting a rope for either a finger line or pilot line it shall have good insulating qualities and be of adequate strength for the tension being applied to it.
Pulling ropes of adequate size must be used during stringing operations. These are of high quality synthetic material, varying in length to the job and sized to the tensile strength of the tensions involved. Pulling ropes in conjunction with a Pulling machine is an effective way to string conductor.
Pulling ropes when not in use should always be covered with a tarp in order to lessen the damage to the rope from the sun's ultra violet rays.
Stringing blocks or rollers should have certain properties common to conventional stringing and tension stringing procedures.
- The throat of the rollers should be of sufficient width to allow the passage of conductor grips.
- The sheave should be hard aluminum or magnesium as this material prevents conductor damage.
- The rollers should have good bearings, which are designed to withstand a static load equal to the roller's ultimate strength. Bearings must be kept greased and free of contaminates.
- The ratio of the diameter of the sheave to the conductor diameter should be in the range of 15-20 to 1.
- The frame should extend above the sheave to prevent the conductor or pulling line from coming out of the sheave.
- The roller should have a smooth rounded frame at the throat to minimize damage to the conductor if it contacts the frame.
- The roller should be capable of accepting some form of a grounding device.
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Examples of various stringing blocks and their applications are found in Figure 4.
Vertical 22 ½ º 45º 67 ½ º 90º
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Running boards are generally not used for conventional stringing operations but are commonly used for tension stringing when pulling in multi-conductors. The running board is designed to correct its position relative to the travelers either in a corner or on a tangent pole and seat the conductors in the conductor sheaves.
Figure5
Automatic splices should not be used for tension or slack stringing applications. Even though they provide a fast, easy method of joining two conductor ends, the sleeves are stiff and bulky. They do not pass easily through rollers, especially on corners and may snag in a roller or fail due to the internal jaws becoming misaligned or the sleeve body cracking.
Conductor reels (see Figures 6a and 6b) must be inspected to ensure they are in good condition. The preferred reel for tension stringing is steel, but if wooden reels are used, ensure that only new conductor is used and is properly wound.
Inspect a wooden reel for rotting around the hub and ensure that the reel bridle on the axle of the stringing equipment fits in snugly to avoid the reel from disengaging and becoming free wheeling.
Figure 6a Figure 6b
Grounding of conductor reels varies depending on the type of equipment being used. The reel stand site must have good grounding possibilities such as an existing system neutral, temporary or permanent ground rods. In conventional stringing operations utilizing reel stands, connect the conductor ends where they come through the side of the reel using no less than # 2 AWG copper to the studs on the side of the reels. See Figure 7.
The studs are fastened to a steel plate installed on the reel, which makes contact with the steel axle. The reel stand is then connected to a ground using no less than # 2 AWG copper.
Figure 7
Grounding the Conductor, Reel And Stand
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With some types of hydraulic tension machines, a bonding lead can be connected from the tail of the conductor through the side of the reel to the grounding lug of the drive arm of the tensioner. An internal collector ring on the shaft provides an electrical path through a set of brushes and a copper lead to an external ground lug on the tensioner.
A portable grounding lead can then be installed between the ground lug and the bonding lead around the perimeter of the gradient mat.
Conventional stringing is permissible when there are no electrical or physical hazards or the hazard of uncontrolled loss of tension of the conductor has been adequately considered, physical precautions have been taken, and a suitable procedure has been put into effect. As mentioned before, conventional stringing methods would apply in cases where positive control of the conductor sag is not a requirement.
There are several methods and variations of methods for conventional stringing on distribution lines. It may involve dragging the conductor out on the ground by some means of a pulling vehicle. When the conductor is dragged past a supporting structure or pole, the pulling is stopped. The conductor is then hoisted aloft to the lineworker who in turn sets it on the insulators in loose ties for sagging purposes.
Pulling the conductor through rollers using a pilot line attached to a finger line is the alternative variation of conventional stringing.
The conductor reels are positioned on reel stands either placed on the ground or a vehicle. See Figure 9. The conductor stands are designed to support the reel on an axle or arbor. Some form of a braking device is often required to prevent the reel from over spinning.
Figure 9
It is often done for a short pull where both ends are within easy sight of the crew. Conventional stringing methods are mainly applicable to construction of new lines. It is not a practical method of stringing where there is danger of contact to energized conductors or where traffic conditions restrict the function of the crew.
TENSION BRAKE DEVICES (for CONVENTIONAL STRINGING)
Various types of tension brakes are available on the market that are both mechanical and hydraulic. These braking devices provide some degree of sag control during conventional stringing operations. They do not, however, have the capability of reversing the direction of pull and therefore are not to be confused with tension stringing methods.
Numerous types of reel brakes are used strictly for conventional stringing operations. They may be the "bogey" wheel type. See Figure 10. This is a unit that mounts on the reel trailer or truck. The conductor traveling through a series of bogey wheels is controlled by friction with the force being increased by a hand-adjusting crank.
Figure 10
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Smooth even control of the conductor backlash or overrunning can be maintained by the use of reel stands with a disc brake assembly that can be easily adjusted during stringing operations. See Figure 11. The reel stands can be the older style laying directly on the ground or mounted on a trailer or flatbed truck.
Figure 11
Other types of braking systems could be the brake band adjusted by a spring to vary the degree of braking action. See Figure 12. This unit can be mounted on all types of conductor reels.
Figure 12
There are other various types of mechanical friction devices that are not commonly used today due to its inefficient braking action. Keep in mind that complications often arise when using poor quality braking devices.
Hydraulic braking devices are also available which incorporate same principles as the mechanical disc brake system but are activated and controlled with a small hydraulic unit mounted directly on the trailer or plumbed in and activated by an auxiliary source of hydraulic power such as an digger derrick.
PULLING DEVICES (FOR CONVENTIONAL STRINGING)
Various types of pulling devices are incorporated during conventional stringing procedures as mentioned earlier in the module. The use of the boom tip winch for pulling conductor during stringing should be discouraged. The internal mechanism of the boom tip winch is not designed to withstand continuous operation during prolonged stringing operations. It may become overheated internally and fail resulting in total loss of control of the conductor.
The use of the collapsible take-up reel or commonly referred to as a butterfly wheel should be limited to slack stringing operations because of the possibility of increased tensions during conventional stringing utilizing some form of braking devices.
Conductors can be pulled by the means of a capstan head either in conjunction with a truck mounted deck winch or by special application hoists such as the Chance Stringer Systems. The Chance devices attach directly to a pole and come in various modes of power being gas, electric and hydraulic. Many combinations of accessories as well as pulling capacities make this device rather economical and portable. The Chance System is similar in setup and operation as the Timberland Poleboss System.
The Poleboss is a lightweight and compact hydraulic system that is ideal for installation of distribution conductors. It can also be used as a pilot rope pulling system in conjunction with tension stringing equipment for the purposes of tension stringing. The Poleboss pulling system consists of:
The Poleboss Puller (see Figure 13) with two ratchet straps and two hydraulic hose connections that provide a maximum pull of 1000 lbs. An adjustable relief valve allows the operator to set the maximum line pull to a safe limit where a snag of the rope will stall the drive and prevent over pull damage.
Figure 13
PoIeboss PuIIer
The Payout Spindle (see Figure 14) with one ratchet strap incorporates a hotstick adjustable overspin brake. The drum contains 3,280 feet of 3/8 braided ropes with a breaking strength of 5800 lbs with a safety factor of 5.8 to 1.
Figure 14
Payout Spindle
Trailer mounted pullers and truck mounted pullers are the most expensive and are generally used for large stringing operations. These pulling machines will be discussed later in this module under tension stringing. By combining a pulling machine with the pole mounted tensioners as mentioned above produces an effective means of conventional stringing practices.
The job of stringing conductors under tension involves complex planning and coordinating the crews actions. Compromising any work procedures and safety rules places all of the crew in jeopardy. Breaking down job steps will help us focus in on key functions of crew members and job actions Once the line has been built, old conductor secure, down guys in place and any other pie-stringing requirements are complete the following steps are to be considered:
- Inspect the line for pulling in new rope and conductor.
- Install the pilot line.
- Set up puller and tension machines.
- Pull in the pulling rope.
- Pull in the conductor.
- Sag conductor.
- Tie in/clamp in the conductor.
- Temporary deadend the conductor.
- Clean up.
Pre-stringing line inspection will establish the puller/ tensioner locations and any road crossings which will hamper the job. Check the pole height, clearances to energized circuits, travelers or stringing blocks are level. The finger lines will assist in pulling in the pilot line so check that they are in place. All guy requirements whether temporary or permanent should have been installed. Cover-up requirements should be either installed now or planned for the actual day of stringing. If possible make sure that the travelers are not centered directly over an existing under build circuit
Install the pilot line using any one of a number of systems. They may include the "Poleboss System" manufactured by Timberland, (see Figure 15) the KB. Chance "Stringer System" or the "Spider II System" manufactured by Sherman & Reilly Inc. These systems consist of a positive braking controller and a storage reel of rope. The storage reel must be kept clean and dry to avoid contamination.
Figure 15
The brake on the controller or payout spindle (Figure 14) allows the reel to pay out the pilot line when the rope is pulled and engages when the rope becomes slack. The braking action eliminates any back winding and holds tension during the installation of the pilot line.
Steps to follow for the installation of the pilot line are:
1. Mount a reel unit per phase on the lead or first pole in front of the tensioner.
2. Pull out each pilot rope under controlled braking and pass it through the stringing blocks on each pole.
3. At the puller end attach temporary helpers on the pilot line to hold in position.
4. When ready to install the pulling rope, remove the reel from the pole and install it on the tensioner.
5. Attach the pilot rope to the pulling rope, remove the temporary helper from the corresponding pilot line and pull it in under controlled tension.
In certain situations the pilot line is installed a few days prior to the actual setting up of the puller and tensioner machines as depicted in Figure 15, in which case only the above steps 1,2 and 3 will be performed.
Setting up of the puller is a critical part of the actual stringing process. Generally the puller would be positioned at the end of a pull where the most obstacles are. This is so you are not pulling all of the conductor over the toughest part of the pull.
All machines should be set back a distance of three times the height of the first roller. If the machine is more than 50 off centerline then the first pole should be guyed.
Three steps to follow for the puller set-up are:
1. Position puller and level using planking and jacks.
2. Anchor the puller to large vehicle or install a temporary anchor and guy.
3. Ground the puller in accordance with section 410.1 of the Pike Electric, Inc. Safety Manual.
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Figure 16
Figure 17
Note: Proper anchoring of pulling and tension machines is extremely important. In some cases it may be necessary to anchor tension and pulling machines three ways to prevent them from overturning where there are higher tensions on the machines.
Depending on specific manufacturers the controls on puller/tensioner machines may vary. On more common equipment the following controls perform specific functions.
1. Hydraulic gauge showing hydraulic pressure.
2. Line pull control which regulates hydraulic pressure. Increasing or decreasing the hydraulic pressure determines stall or snag capabilities.
3. Brake control either applies or releases the spring brake by hydraulic pressure.
4. Direction control lever increases or decreases hydraulic pressure whereby increasing or decreasing the speed of pull. This control also determines the direction of pull whether payout or pull in mode.
5. Direction lever stop is a mechanical failsafe device or interlock which must be manually raised to allow the direction control lever to be operated.
6. Level wind direction control (optional) operates the level wind post sideways.
7. Level wind speed control (optional) regulates the speed of the sideway movement of the post.
8. Front jack control (optional) operates the hydraulic jack mounted at the front of the unit.
Figure 18
A pre-operational check ensures that the tensioner and puller machines are working. Follow these steps to complete the check.
1. Start the engines with hydraulic system disengaged.
2. Allow the engines to warm, check and if necessary adjust the hydraulic fluid level in the reservoir.
3. Engage the hydraulic pump and allow the fluid to warm up.
4. Set the jacks to level the machines and bypass their system to prevent inadvertent movement.
5. Check and adjust if necessary the hydraulic fluid level.
6. Check that the reels and brakes are functioning properly by putting the reels in motion both forward and backward and testing both the "manual" and "automatic" brakes. An engine operating at idle speed does not sufficiently power the hydraulic system and may let the brake drag.
R-Switch Work Protection is a must prior to beginning any pull of the stringing rope.
Pulling line installation is accomplished with the pilot line drum installed on a tension machine and the pulling machine feeding the pulling line. See Figure 19. This procedure is listed as follows:
1. Attach the pilot line drum on to the tension machine drive shaft making sure the rope pays from the top of the drum.
2. Attach the pulling line to the pilot line using a Kellem grip and swivel sized to suit both ropes and the tension.
3. Set the tensioner, with the pilot line attached to "Pull In" mode.
4. Begin winding in the pilot line, maintaining tension on the pulling line.
Note: Be careful not to exceed 300 pounds of line pull while installing the pulling rope. Damage to the pilot line drum, the rope or personal injury may result if overloading the drive system. ‘Ibis maximum line pull is reached at different hydraulic pressures depending on the type of equipment and the amount of rope on the reel. Less hydraulic pressure for an empty reel and more pressure for a full reel.
5. Set the puller to "Pay Out" as the tension comes onto the pulling line.
6. When the pulling line reaches the tensioner, stop the machine and apply the brakes.
7. Grip off the pulling line to maintain tension.
Figure 19
With the pulling line in place, the pilot line drum can be removed from the tensioner, a reel of conductor installed and the running board attached on single conductor pulls a running board is not required.
If pulling multi-conductors and using gang rollers check to see the position of the pulling rope is in the center of the traveler for the running board to pass through with ease. Identify field conductor and corresponding tension machine with fluorescent paint or a flag for easy reference.
The wire reels must be grounded and the axle bridles properly installed as in Figure 20.
Figure 20
Note: Check the condition of the reels carefully if using wooden reels as a considerable amount of force is exerted on the hubs from the axle bridle. If it becomes dislodged due to improper installation or fatigue then the reel will become freewheeling causing serious consequences.
410.1 Pike Electric, Inc. Safety & Training Manual
3. Running grounds shall be used in wire pulling operations when working in close proximity to energized circuits or circuits that may become energized. The running ground and the wire pulling equipment shall be connected from the conductor being pulled to the system neutral prior to the operation of the wire pulling equipment. (Any deviation from the above shall be approved by the immediate supervisor or employee in charge. Penalty shall be imposed on the employee in charge at the location.)
4. When operating a wire puller or tensioner in any area where the conductor being pulled could become energized, the puller or tensioner shall be isolated from other pieces of equipment by using an insulated rope, nylon sling, or other insulated material.5. Mobile equipment grounds shall be placed on the common neutral from the aerial bucket by using an approved live line shotgun stick.
Figure 21
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Pulling in the conductor in a multi-conductor pull is accomplished by the following steps:
1. Begin with the center phase tension machine and slowly start to take up slack until the weight of the pulling line at the tensioner is taken up and the helper or safety grip begins to slacken and stop.
2. Remove the safety grip from the pulling line at the tensioner end.
3. Take up slack in the road phase tensioner just until the center phase reel begins to turn and stop. Remove the safety grip from the pulling tire.
4. Move to the field phase tensioner and take up slack until both the center and road phase reel begin to move and stop. Remove the safety trip from the pulling line.
5. Check the hydraulic tension gauges. All three-tension machines should be set at approximately the same hydraulic pressure.
Note: In the case of a single conductor pull using one puller and one tensioner, (see Figure 22) steps 3, 4 and 5 will be eliminated and the speed of the pull may increase slightly.
6. Notify the puller operator to begin the pull.
7. Once tension at the puller has been applied stop the puller and remove the safety grip at the puller end.
8. Begin the pull under the direction of a crewmember designated to follow the running board. Release the brake control and increase the hydraulic pressure until the pulling rope begins to move. The puller should have hydraulic pressure in the system slightly above the tensioner to overcome drag.
Note: It may be necessary to adjust the hydraulic pressure several times from the initial setting as the pulling rope builds up on the reel. Always maintain hydraulic pressure at the puller slightly above the hydraulic pressure at the tensioner as this will ensure the puller stalls if any snag occurs on the rope or conductor.
9. When the pulling rope passes through the last traveler the pull is stopped by the puller operator. On some manufacturers move the direction control lever to the neutral position and apply the brake.
The speed at which the running board travels on multi-conductor pulls should be no more than 5 mph.
Figure 22
Note: During stringing operations, no worker shall be aloft on any pole while the conductor and pulling rope are in motion. Before any work is done on the conductors, temporary grounds must be installed for personal protection.
Paying out or loosening a pulling rope or conductor may be required while it is under tension. This process back reels conductor at the puller end by hydraulic pressure being greater at the tensioner or load end.
Ending the pull:
1. Install temporary grips or permanent deadends at the puller end and leave enough tail for splicing if required.
Figure 23
2. Release tension on the pulling line and disconnect it from the running board or swivel.
3. Sag the conductor at the tensioner end using the machine to take up slack. This can be either a pre-sag condition or final sag.
4. When the conductors are at sag and gripped off at both ends, release the tension and cut the conductor.
Clamping in or tying in the conductor can be accomplished only after grounds are applied on the new conductor and any existing circuit if it has been isolated and is in close proximity.
nging.
