VR2 Conductor Installation Guide

1.0 INTRODUCTION

This guide provides recommendations on procedures and equipment used during VR2 conductor installation. VR2 conductor can be installed using techniques and equipment similar to that used when installing standard round conductor. These general guidelines, together with those suggested in the IEEE Guide to the Installation of Overhead Transmission Line Conductors (IEEE 524TM –2003), will provide the basic information required to install VR2 conductor.

2.0 VR2 CONDUCTOR STRINGING METHODS

There are several stringing methods available for VR2 conductors; however the method chosen must be appropriate for the installation requirements. A brief description of these stringing methods is described below.

2.1 Slack Method

The VR2 conductor reels are mounted on stands or jacks and are free to rotate with only enough braking force to prevent overrun backlash or loops. The VR2 conductor is pulled off the reel by a vehicle that stops at each structure where the conductor is lifted and placed in a traveler mounted on the structure.

2.2 Layout Method

This method is similar to the slack method except the lead end of the VR2 conductor is tied off and the reel is mounted on a vehicle which travels down the line paying out the conductor as it goes.

2.3 Semi-Tension Method

This method follows the general procedure of tension stringing, except no tensioner is used. Minimal ground clearance is maintained by applying slight braking force to the conductor payout reel. Caution: The reels are not designed to withstand elevated tensions or high braking forces; therefore the conductor tension must be kept sufficiently low to prevent damage to the conductor or reel.

2.4 Tension Stringing Method

The tension stringing method is the most common installation method. This method consists of a pulling line threaded through a stringing sheave on each structure of the pulling section and connected to a swivel and pulling grip attached to the leading end of the conductor to be installed. The conductor is pulled through the sheaves of the stringing section as the pulling rope is wound onto the drum of a drum type puller, located at the pulling end of the stringing section. The pulling tension is regulated by the bullwheel tensioner located at the conductor pay out end of the stringing section between the conductor reel and the first structure. Only
minimum braking force is applied to the payout reel to prevent over-run in the event of a sudden stop. This installation method keeps the conductor clear of the ground and other obstructions that could damage the conductor. Pulling tension should never exceed the sagging tension for the installation.

2.4.1 Tension Stringing Equipment

Tensioners

When tension stringing VR2 conductor, a multi-groove tandem bullwheel tensioner is recommended. The
alignment of the bullwheels should be offset by approximately ½ the groove spacing to allow proper tracking
of the conductor around the bullwheels. Either the offset or tilted type bullwheel configuration shown above
may be used. The two primary considerations when selecting a bullwheel tensioner are groove radius and
bullwheel bottom of groove diameter. Proper groove radius and bullwheel diameter are specified in IEEE 524.
The maximum conductor diameter for VR2 cable is twice the diameter of one component conductor.

• The groove radius must be large enough so that the conductor, when laid flat, will fit into the bottom third of the groove.
• The bullwheel sheave diameter must be large enough to avoid excessive bending of the conductor. The recommended minimum bullwheel bottom of groove diameter should not be less than 35 times the maximum conductor diameter.
• The two-tensioner bullwheels must be closely synchronized to minimize conductor assembly separation as it traverses the bullwheels. Also, the tensioner’s braking system must allow for smooth, consistent tensioning of the conductor from stop to full payout speed and back to stop.
• For standard VR2 conductor (individual conductors with a right hand direction of lay and a left hand direction of lay for the twisted assembly) the direction of wrap across the bullwheel should be from left to right.
• One (1) or two (2) wraps of the conductor around the bullwheel should be sufficient for normal pulls.
No more than three (3) wraps on the bullwheel are recommended for typical installations.

2.4.2 Tension Stringing

Proper positioning of the stringing equipment is crucial for a good installation. The tensioner should be aligned with the sheave at the first structure and in line with the pull section. It is recommended that the angle of the conductor between the ground and sheave at the first structure be approximately 15 degrees, and should never exceed 25 degrees. Practically speaking, the tensioner should be positioned back from the first pole or structure a distance of three or four times the vertical height of the entrance stringing sheave. For example, for a 15-degree angle, if the first sheave is at a height of 25 feet then the tensioner should be set back at least 100 feet from the structure. This practice will minimize the bending radius of the conductor and contact force between the conductor and the sheave, reducing the tendency of the conductor to separate.

The payout reel should be positioned in line with and behind the tensioner. The conductor payout reel should be positioned 50 to100 feet behind the tensioner to allow the conductor to adjust from the circular wrap on the reel to a straight orientation before entering the bullwheel tensioner. Care should be taken to avoid excessive bending around small fairlead rollers on the tensioner. The braking tension on the payout reel should be set only high enough to prevent overrun when the pull is stopped.

Excessive payout tension may distort or damage the conductor. If a guide roller is required to guide the conductor over other reels or obstructions, the guide roller or sheave should have a bottom grove diameter approximately 14 times the maximum diameter of the conductor.

3.0 SHEAVE REQUIREMENTS

The recommended minimum sheave bottom groove diameter should be 14 times the maximum diameter of the VR2 conductor. The entrance sheave and angle sheaves, for angles greater than 15 degrees, should be larger. Proper size will be evident by smooth passage of the conductor through the sheaves, minimizing conductor bending and damage. Unlined sheaves are preferred.

• Minimum groove radius: 0.55 times the maximum diameter of VR2 conductor.
• As discussed previously, the groove radius must be large enough so that the conductor, when laid flat, will fit into the bottom third of the groove.

Refer to IEEE 524TM –2003 for more sheave related recommendations.

4.0 STRINGING VR2 CONDUCTOR

The conductor is shipped from the manufacturing plant with two metal band clamps on each end of the conductor. One clamp is near the end of the conductor and another clamp is located five (5) to ten (10) feet from the ends. It is important to keep both clamps on each end of the conductor during stringing to prevent relative movement of the component conductors, which may cause bagging. The conductor pulling grip (Kellem grip) should be installed over the banded cable. If the pulling grip will not fit over the conductor band clamps, additional band clamps should be
installed on the conductor before the clamps installed at the factory are removed.

5.0 TENSIONING VR2 CONDUCTOR

During tensioning and or mid-span splicing of VR2 conductors an equalizer sling must be used to maintain equal tension in each conductor.

• Separate grips must be placed on each of the component conductors. The two grips are then connected through a snatch block with a sling, as shown below:

• Pulling is done against the snatch block. This pulling assembly is often called an equalizer sling. This insures that both conductors take an equal share of the pulling load, which prevents unequal tension and helps maintain the relative positions of the component conductors. This will also tend to correct any change in relative component conductor position that may have occurred during the stringing process.

6.0 SAGGING VR2 CONDUCTOR

Presently accepted sag methods for standard conductors are satisfactory for VR2 conductor. Use sag values supplied by the Utility or by Southwire Company.

7.0 DEADENDING

There are a variety of different styles of deadend hardware available. Bolted type quadrant and compression type deadend clamps work well. However, always consult with the accessory manufacturer for the correct selection and installation procedure for the hardware.

8.0 SPLICING
VR2 conductor is joined by separately splicing the component conductors, with approximately 5 feet between the splices. Care should be taken to maintain equal tension on the component conductors to prevent them from separating.

9.0 INSTALLATION PRECAUTIONS
VR2 conductor consists of two component conductors twisted together with a lay that varies with conductor size. However, the lay may vary due to twist migration and conductor rotation during installation. In extreme situations this may result in separation of the component conductors, commonly called a bag. This rotation may be caused by factors including installation method, sheave diameter, tension and pole spacing. It is helpful to identify the point where bagging first begins to correct the source of the problem.

Slight separation of the component conductors is normal as it is paid off the reel and sometimes during stringing. Tension equalization between the conductors during the stringing operation should correct the problem.

If conductor bagging remains after stringing, these bags can typically be worked out during conductor tensioning. With the equalizer sling attached, bump the VR2 conductor with a rope to cause relative conductor movement. This should allow the bags to pull out.

In the event of major conductor bagging, bags can be cut out and the component conductor spliced.

This publication is a collection of items of general information related to the subject of VR2 conductor. It is not intended to be nor should it be used as authority for design, construction, use or installation. The design, construction, use and installation of VR2 conductor should only be undertaken by competent professionals in light of currently accepted design and engineering practices.

While great care has been employed to ensure that the applications, tables, standards and references and other information contained herein are free of errors, absolutely no warranties, either expressed or implied, are made as to the accuracy or completeness of any such tables and formulas contained herein.

THOSE PREPARING AND/OR CONTRIBUTING TO THE PUBLICATION SPECIFICALLY DISCLAIM ANY WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED. THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE HEREBY SPECIFICALLY DISCLAIMED BY SOUTHWIRE AND ALL OTHER PARTIES INVOLVED IN THE CREATION, PRODUCTION, OR DELIVERY OF THIS PUBLICATION.

Neither Southwire nor anyone else who has been involved in the creation, production or delivery of this publication shall be liable for any direct, indirect, consequential, or incidental damages arising out of the use, the results of the use, or inability to use such publication, even if Southwire has been advised of the possibility of such damages or claim. Some states do not allow the exclusion or limitation for consequential incidental damages, so the above limitation may not apply to you.