PROJECT OVERVIEW

Project: New overhead transmission line in ice-prone region

Product Used: Southwire VR2 VibrationResistant twisted pair design

In-Service Date: February 2008

VR2 Makes Twisted Pair Conductor Installations Easy.

Where the winds blow free across the open spaces of the Midwest, aeolian vibration, ice storms and ice galloping are serious problems for overhead transmission and distribution lines.

When a large Midwest utility company was looking to utilize a better ice galloping preventative conductor for its electric operations, the company turned to a newly released product from Southwire: VR2 Vibration Resistant twisted pair cables. In the company’s installation, VR2 made twisted pair conductor installation easier than the old twisted pair cable design.

VR2 Design Eliminates Bagging

Traditional vibration-resistant cable constructions have a history of being temperamental during installation. VR2, a new design from Southwire, solves the problem.

For the utility company, severe ice storms are a fact of life. The company estimated that restoration costs after a major ice storm in February of 2007 were in the neighborhood of $70 million. “We saw anywhere from 1-2 ½ inches of ice on conductors,” says a project manager with the company.

Standard ice-galloping answer: twisted pair cables
For years, the standard preventive measure for aeolian vibration and ice galloping is to install cables made up of two individual stranded conductors twisted together. Southwire’s traditional version of this twisted pair construction was called VR or Vibration Resistant cable.

“Ice can add six or seven times the conductor weight to a line, and ice galloping breaks wires and pulls down poles,” says the project manager. “Twisted conductors tend to accumulate less ice, because of its design which allows ice to fall off once it starts to accumulate.”

Bagging problems slow installation
The problem with traditional twisted pair designs is that they can be temperamental to install. When two-conductor cables are pulled off the reel, or through sheaves, sometimes the cable will try to un-twist. The conductors separate, and one of them may sag away from the other and form loops called “bagging”. Fixing bagging issues is time-consuming and labor-intensive for crews.

Company received Southwire technical support
In the summer of 2007, the utility crews encountered bagging problems when stringing traditional twisted pair cable. The utility company turned to Southwire for technical support on installation techniques. Southwire engineers worked with the crews to improve stringing practices, advising them on factors such as the size of the sheaves being used. Still, the installation modifications did not completely resolve the bagging problem. That is when the company turned to Southwire for a possible change in the twisted pair design.

Then came a new product: VR2

At the same time, Southwire engineers were working on a new construction design for twisted pair cable. The new product was VR2, a Southwire exclusive using a patentpending construction technique that eliminates bagging. When the company heard about it, they wanted to try it. In early 2008, the first reels of VR2 arrived at the work site.

The company installed the VR2 conductors on a .65-mile
stretch of 69 kV horizontal post insulator. To evaluate
the new design, the company installed VR2 side-by-side
with traditionally-constructed twisted pair conductor
on different phases of the three-phase line. VR2 cable
is third from the left in the photo above. The traditional construction
continued to exhibit bagging problems. The new VR2 went up without a hitch. “The difference was like night and day,” says the project manager.

VR2 gives easy installation, regular appearance
A company travel crew foreman says, “We pull the wire in under tension. The old wire might start to come apart between the reel and the pole, or while it was going down the line. We’d have to put up people in bucket trucks to shake out the loops. The new wire just came in perfectly.”

He adds, “You could stand under the pole and listen to the wire moving through the sheaves. With the old wire, you could hear the twists passing through the sheaves at odd intervals. With the new wire, you could hear it clinking through the sheaves very regularly.”

Even after the installation, the VR2 difference is apparent. The foreman says, “With the old wire, even after we shake out the loops, you can drive down the road and see the irregularity in the twist of the conductor. The VR2 is completely regular. This new wire is good stuff.”

VR2 is now Southwire standard construction “The company has installed about 120,000 feet of VR2 so far, in sizes 1/0 and 4/0,” says Michael Lowry, sales manager for Southwire’s central region. VR2 is another example of Southwire innovation with immediate benefits in the field. All of Southwire’s twisted pair cables will be using the new VR2 construction.”