/images/TDUpdate.jpg/images/southwire_100x70.jpgAdd Steel Strength - Get More Grid Throughput - 2005 testAddSteelStrengthGetMoreGridThroughputJuly2005.htmToday, boosting grid capacity usually means putting more power down the same right-of-way. So, as engineers explore routes to higher throughput, overhead conductor designs are coming under increased scrutiny.
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Add Steel Strength - Get More Grid Throughput - 2005 test

Today, boosting grid capacity usually means putting more power down the same right-of-way. So, as engineers explore routes to higher throughput, overhead conductor designs are coming under increased scrutiny. In that investigation, Southwire's recently developed HS285 ACSS (aluminum conductor, steel supported) cables look very promising, because they add cost-effective strength to the conductor.

"In most overhead spans, capacity will be limited by increasing sag as the conductor temperature goes up. Increased core strength can boost capacity by reducing sag," says Nick Ware, technical director of Southwire's Energy Division.

ACSS is an example of increasing capacity by decreasing sag

In ACSS (aluminum conductor, steel supported) conductors, sag is determined by the low expansion rate of steel, rather than the high expansion rate of aluminum. That allows higher operating temperatures and more capacity than ACSR (aluminum conductor, steel reinforced) cables.

Even with ACSS designs, sag, rather than conductor temperature, is the usual operating limit. If you could stretch the conductor tighter, you could run it hotter before it sags to the point where clearance reaches the safety limit. Conventional ACSS conductors lack the strength required to do that, unless we add additional steel area, which translates to additional weight. That's where stronger steels, such as Southwire's HS285, become a capacity-increasing option. With a little more strength in the wire and in the structures you can put more power through the right-of-way.

Steel strength is cost-effective

For most real applications today, steel is still the most cost-effective route to adding strength to cable cores. Some utilities are currently evaluating lightweight, high-strength alternatives to steel cores, but at present their reliability is still being proven.

"Southwire is watching and working in non-steel core technologies," Ware says, "but we are partial to the familiarity and reliability of the metallic core technologies." "The most promising alternative today is a composite of spaceage fiber in an aluminum matrix. It's a well thought-out product, but it's very costly compared to steel. It's probably cost-justified only in the most extreme applications. A less expensive non-metallic alternative - carbon-fiber surrounded by fiberglass - still costs significantly more than steel, and it needs further evaluation and development before broad acceptance."

For stronger overhead conductors, Southwire's HS285 steel cores provide a costeffective step forward. They also have the advantage of familiar technology with proven performance. Application design, installation, and aging characteristics are all well known.

"Today's grid upgrade mantra is, "Less sag and more capacity," says Ware. "Southwire is continuing to lead the industry in providing practical, cost-effective solutions that fit that formula."

Steel Core Strength Comparison

  • A typical steel core in a standard ACSR (aluminum conductor, steel reinforced) cable has a tensile strength of about 210ksi.
  • 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.

Superconducting Distribution Economics Looking Better

Total cost of ownership in urban areas may be bringing high-temperature superconductors closer than you think.

So you want to add about 100 MVA to a distribution substation in a downtown area. One option is to run a new high-voltage line into the substation. An overhead line? In an urban environment, permitting and rights of way are likely to be serious political problems. Underground high-voltage? That's easier politically than overhead, but the voltage levels still entail a long permitting cycle and some pretty sophisticated civil engineering. And, overhead or underground, you're going to pay downtown prices for the real estate high-voltage transformers will need.

Superconductivity option is on the way

"There's another option on the way from Southwire," says David Lindsay, Southwire program manager for superconductivity. "Pull one 5.5" diameter cable through a relatively simple directional boring and bring the load right into the substation at distribution voltage, ready to connect to a distribution bus. You'll see less permitting, less civil engineering, and no transformer footprint to pay for."

What's the trick with that cable? It's Southwire's new triaxial high-temperature superconducting power distribution medium. The cable has passed qualification testing at Oak Ridge National Laboratory, and is in manufacturing for a 200-meter, 13.2 kV, 3000 Amp (steady state load) demonstration project in Columbus, Ohio.

Manufacturing expertise makes it practical

High-temperature superconductive cables are simple enough in principle. Encase a bismuth-based ceramic material in a silver-alloy tape, pump liquid nitrogen at -321° F (-198° C) around it, and run current through it. The trick is being able to manufacture and install your design.

"Southwire brings advanced cable construction expertise to the superconducting party," says Lindsay. "We're developing designs that we can manufacture and install on a commercial scale. We have been running three factories in Carrollton, Georgia on a high-temperature superconducting link since the beginning of 2000. The new Triax design drives down costs by using about half the high-value materials of earlier designs."

In the new design, all three phases are layered concentrically on one core. That gives a 5.5" diameter cable that delivers the ampacity of about twenty-seven 2,000 kcmil copper conductors. The cable is compatible with standard faultprotection systems for distribution circuits and buses. It easily handles fault currents seen with normal circuit-breaker operation, including automatic recloses.

The triaxial cable is also built to withstand pulling stresses during installation into duct banks. Running at liquid-nitrogen temperatures, the thermal conductivity of the surrounding earth doesn't affect ampacity. And, the concentric configuration of the phases in the Triax cable minimizes EMF effects in steel ducts and nearby steel utilities such as water pipes. Both those points simplify installation design.

Total cost of distribution can drive the economics

"When you look at the total project cost for adding power to urban distribution circuits, high-temperature superconductivity starts to sound nearer to economic reality than you may have thought," says Lindsay. "We're aiming at energizing the demonstration line in mid-2006. That's one step closer to a commercial installation."

Easy Savings on Steel Strand

Adding steel strand to a consolidated order can cut the cost of this utility staple.

Whether it's guy wire, messenger cable or overhead lightning protection, when you place a separate order for steel strand wire you could be spending more money than you need to. Steel strand from Southwire may save you those extra dollars.

"Ordering from multiple suppliers costs utilities money," says Norman Adkins, Vice President, Energy Division. "Multiple orders take more time for the ordering itself, more time to receive shipments, more time to check and process invoices. There's also less opportunity to take advantage of combined-order discounts and consolidated freight rates. Adding steel strand to a Southwire wire and cable order can eliminate those costs."

Get the steel strand specification you need

Southwire can supply steel strand wire in diameters from 1/4" to 1/2", in 3-, 7- and 19-wire constructions, depending on the diameter. Five strength grades are available:

  • Common
  • Siemens Martin
  • Utilities
  • High Strength
  • Extra High Strength .

The strength grades give a wide range of breaking strengths. For example, in a 3/8" diameter, seven-wire construction, Common grade provides a 4,250-pound minimum breaking strength, Utility grade delivers 11,500 pounds, and Extra High Strength 15,400 pounds.

Southwire can provide steel strand with class A, B, and C galvanized coatings, where class C provides approximately three times the coating material that class A does. Galfan coating is also available. Aluminum-rich Galfan coatings deliver corrosion protection that is superior to traditional galvanizing.

Use steel strand as guy wire or messenger cable

Steel strand wire used for guying structures or as a messenger for electrical conductors must have a high elastic limit, excellent tensile strength, durable resistance to corrosion, and good fatigue properties. You can count on Southwire for top-quality steel strand wire that meets all applicable RUS specifications and ASTM standards.

Use steel strand as overhead lightning protection

Steel strand is also used as an overhead ground wire or static wire on transmission towers to prevent lightening strokes from reaching the conductors. Static wires must be large enough so that lightening surges won't burn through the cable - in most cases, at least 3/8" in diameter.

Overhead static wire is available from Southwire with no joints or strand splices in the completed strand, per ASTM-A363. This specification helps insure that lightening current travels safely to ground without resistance or interruption.

Choose from several packaging options

Steel strand wire is available from Southwire in

  • 250 ft and 500 ft coils
  • 1,000 ft, 2,500 ft and 5,000 ft reels
  • Custom lengths to meet your job requirements

"In addition to standard products, Southwire can also provide steel strand to meet your special requirements or specifications," Adkins says. "This is another addition to Southwire's support of our utility customers."

For more information on steel strand from Southwire, including specific product details, contact your Southwire representative.