Overhead Conductor Installation Guide Recommended Practices First Edition 3.2 Semi-Tension Method This method is similar to tension stringing except in this method the conductor is pulled directly off the pay-off reel and into the spans. Minimal ground clearance is maintained by applying gentle braking force to the let-off reel. It is important to recognize that the amount of braking force must be kept to an absolute minimum level. Excessive braking force cannot only damage the remaining conductor on the reel, but it can also damage or collapse the reel itself. This method must not be used for the installation of TransPowr® ACSS, ACSS/TW or multilayer transmission size conductors. 3.3 Layout Method This method is similar to the slack method except the lead end of the conductor is tied off and the reel is mounted onto a vehicle or trailer which travels down the line section, paying out the conductor as it goes. The conductor is then lifted and placed into a stringing sheave at each structure. This method must not be used for the installation of TransPowr® ACSS, ACSS/TW or multilayer transmission size conductors. 3.4 Slack Method This method consists of mounting the conductor reel on stands or jacks, leaving it free to rotate with just enough braking force on the reel to prevent over-run, backlash or loops. A vehicle, to which the conductor is attached, is driven past each structure while pulling out the conductor. At each structure, the conductor is lifted and placed into a stringing sheave. A stringing sheave may also be referred to as a traveler, block, dolly, sheave, stringing block, or stringing traveler. The vehicle continues to the end of the line section being installed. This method must not be used for the installation of TransPowr® ACSS, ACSS/TW or multilayer transmission size conductors. 4 TENSIONER TYPES Bullwheel tensioners rely on friction between the bullwheel and the conductor to create tension in the conductor. To increase the area in contact between the two, multi-groove bullwheel tensioners are used. In order to wrap the conductor into the grooves, two wheels in tandem are used. Two different bullwheel tensioner types—offset and tilted—are used to transition the conductor from the back wheel to the front wheel. Bare aluminum conductors are built with a right-hand lay on the outside layer, so the bullwheel tensioner, regardless of the type, must be a right-hand lay design. As recommended by IEEE Standard 524, the conductor enters the tensioner from the top left-most groove of the front bullwheel and exits from the top right-most groove of the back bullwheel. All grooves of the bullwheels must be used. Combination Bullwheel Tensioner/Pay-off Trailers and V-Groove Tensioners are also suitable for the installation of small conductor sizes. These tensioner types are discussed in more detail in Sections 4.4 and 4.5. 4.1 Offset Multi-Groove Bullwheel Tensioner Figure 1 illustrates an offset multi-groove bullwheel tensioner. The front and back bullwheels stand vertical but are offset by half a groove’s width. It is important that the radius of the grooves, and the bullwheel diameter at the bottom of the grooves, be sized correctly. The offset multi-groove bullwheel tensioner has been used successfully for many years.
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Overhead Conductor Installation Guide
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