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Project Profile: CenterPoint Energy

PROJECT OVERVIEW

Project: Hillje Project                                       Electrical Contractor: InfoSource                         


Location: Houston, Texas                               Product Used: Southwire ACSS/TW HS285®               


Project Owner: CenterPoint Energy              In-Service Date: July 2007


High-Capacity Tie Line Uses Low-Sag Technology

When Houston-based CenterPoint Energy needed to upgrade a tie line between two major generating stations, their choice was a new product from Southwire that delivers high-temperature, low-sag capacity rivaling exotic composite-coredesigns – without the exotic cost. The wire CenterPoint chose puts an ultra-high-strength steel core inside an ACSS/TW conductor architecture. (See box for details of the HS285 ultra-high-strength ACSS/TW architecture)

CenterPoint’s challenge was to bring more power to the greater Houston area. They needed increased transmission capacity between a nuclear plant near Bay City, Texas, and a generating facility in Rosenberg, Texas. The solution was an $80 million, 60-mile, two-circuit 345kV transmission line. The question was how to implement the circuits.


High-Temperature, Low Sag HS285 Won Over Many Options

CenterPoint analyzed 60 different design combinations, factoring in distance between structures, land-use impacts, construction issues and total installed costs. Circuit options included: two conductors using ACSR (aluminum conductor, steel-reinforced); three conductors using standard ACSS/TW (aluminum conductor, steel-supported, trapezoidal wires); and two conductors using Southwire’s new HS285 ultra-high-strength ACSS/TW high-temperature, low-sag design.

CenterPoint found that the new HS285 ACSS/TW conductors would give 55 percent more capacity than the ACSR conductors with a project cost premium of only about four percent. That made the decision clear. Forty miles of the line will use new structures to carry two 1433.6 kcmil ACSS/TW HS285 conductors. That installation was energized in July 2007.

Chuck Bennett, Manager of Transmission Engineering for CenterPoint, says, “We would have used HS285 for the entire project, but testing time and early product availability didn’t quite meet schedule requirements for the first phases. For the same scheduling reasons, we originally designed our new structures for the reduced sag of standard ACSS/TW. Reduced tower height saved several hundreds of thousands of dollars over the ACSR option, but even then we didn’t make full use of HS285 economies. HS285 will reduce maximum sag by yet another three to four feet.”


HS285 rivals composite-core designs

The new HS285 is an enhanced version of Southwire’s ACSS/TW. Like standard ACSS/TW, HS285 is rated for continuous operation at 250°C. An ultra-high-strength steel core puts HS285 sag performance on a par with recently developed composite cores “…at a reasonable cost, not 10 to 30 times the price,” according to Bennett.

The ultra-high-strength steel core material borrows heavily from existing steel technology to develop high tensile strength without loss of elongation, ductility or stress corrosion properties.

The HS285 core is protected by a Galfan coating that contains 95 percent zinc and about five percent aluminum, with a small addition of rare earth elements, primarily cerium and lanthanum. The Galfan coating protects the steel core at operating temperatures that would shorten the life of traditional galvanizing.

“The advanced HS285 steel core lets us get more strength with tested and known technology,” says Nick Ware, Vice President, Technical for Southwire’s Energy Division. “The higher strength of HS285 ACSS/TW lets us pull the cable tighter at installation. That helps sag performance and allows shorter, less expensive support structures.”

In addition to cost advantages, another  advantage of HS285 over exotic composite conductors is that it uses the same installation techniques as standard ACSS. HS285 is commercially available with lead times in line with conventional ACSR conductors. 


CenterPoint Sees Future Uses

Bennett says, “We have a long history with the ACSS/TW cable architecture. We have been using ACSS/TW since 2000, and have installed over 3,000 miles of it.”

CenterPoint sees HS285 ACSS/TW conductors as an economical solution for increasing capacity needs. The additional mechanical strength will also meet new needs The 2007 National Electrical Safety Code will require higher mechanical loading design criteria, and the Texas PUC may be considering higher hurricane storm-loading criteria. “This is a good option to have in our toolbox,” says Bennett.

 

If you need increased capacity in a new line, Southwire HS285 is the multi-purpose tool you need. Call your Southwire representative or visit http://www.southwire.com/ today to learn more.