/images/buttons/swirl_60.jpg/images/southwire_100x70.jpgHigh-Capacity Tie Line Uses Low-Sag Technology - 2007HiCapacityTieLineUsesLowSagTechJan2007.htmUltra-high-strength steel core delivers exotic performance with known technology.
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High-Capacity Tie Line Uses Low-Sag Technology - 2007

Ultra-high-strength steel core delivers exotic performance with known technology.

When Houston-based CenterPoint Energy needed increased tie-line capacity between a nuclear plant near Bay City, Texas, and a generating facility in Rosenberg, Texas, they looked at many options. They chose a new product from Southwire: HS285 ACSS/TW.

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.) The combination delivers high-temperature, low-sag capacity rivaling exotic composite-core designs, without the exotic cost.

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. The solution was an $80 million, 60-mile, two-circuit 345kV transmission line.

CenterPoint found that the new HS285 ACSS/TW conductors would give 55 percent more capacity than the ACSR conductors. 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 is scheduled to be in service in May of 2007.

Chuck Bennett, manager of transmission engineering for CenterPoint, says, “We originally designed our new structures for the reduced sag of standard ACSS/TW. Reduced tower height saved several hundred thousands of dollars over the ACSR option. 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, as Bennett puts it, “…at a reasonable cost, not 10 to 30 times the price.”

Where a traditional “high-strength” core delivers a tensile strength of about 235ksi, Southwire’s HS285 steel core racks up 285ksi before failure, 21 percent stronger than the usual “high-strength” core, and 36 percent stronger than a standard core.

“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 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.

Thorough testing came before acceptance

CenterPoint has a history of early adoption of advanced conductor technology, but they are also prudent about their investments. Before committing to the HS285 design, CenterPoint used the Electric Power Research Institute (EPRI) for testing that covered mechanical and thermal performance of the conductor and the support hardware. Those tests complemented testing commissioned by Southwire at National Electric Energy Testing, Research, and Applications Center of Georgia Tech (NEETRAC).

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. This is a good option to have in our toolbox.”