Conductor stringing systems currently employed in the power industry are almost as numerous as the organizations that string conductors. Below is an outline of the basic methods currently in use, but they are invariably modified to accommodate equipment readily available and the ideas and philosophies of the responsible supervisors.
In addition to a description of the various methods being used are comments relative to application and a listing of equipment applicable to each method.
Slack or layout method
Using this method, the conductor is dragged along the ground by means of a pulling vehicle, or the reel is carried along the line on a vehicle and the conductor is deposited on the ground. The conductor reels are positioned on reel stands or jack either placed on the ground or mounted on a transporting vehicle.
These stands are designed to support the reel 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.
This method is chiefly applicable to the construction of new lines in cases in which maintenance of conductor surface condition is not critical and where terrain is easily accessible to a pulling vehicle. The method is not usually economically applicable in urban locations where hazards exist from traffic or where there is danger of contact with energized circuits, nor is it practical in mountainous regions inaccessible to pulling vehicles.
Major equipment required to perform slack stringing includes reel stands, pulling vehicle(s), and a splicing cart.
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 reel stands using specially designed tensioners and pullers.
For lighter conductors, a lightweight pulling line may be used in place of the pilot line to directly pull in the conductor. A helicopter or ground vehicle can be used to pull or lay out a pilot line or pulling line.
The tension method of stringing is applicable where it is desired to keep the conductor off the ground to minimize surface damage or in areas where frequent crossings are encountered. The amount of right-of-way travel by heavy equipment is also reduced.
Usually, this method provides the most economical means of stringing conductor. The helicopter use is particularly advantageous in rugged or poorly accessible terrain.
Major equipment required for tension stringing includes reel stands, tensioner, puller, reel winder, pilot line winder, splicing cart, and helicopter or pulling vehicle.