/images/buttons/swirl_60.jpg/images/southwire_100x70.jpgNew Industry Standards are Guiding Designs and Interconnections - 2009standardsGuideDesign.htmIndustry leader Southwire actively works on critical industry standards.
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New Industry Standards are Guiding Designs and Interconnections - 2009

Industry leader Southwire actively works on critical industry standards.

International guidelines for HV laminate sheaths due this year
CIGRE - the International Council On Large Electric Systems - is less well known in the U.S. than ASTM or ICEA. CIGRE recommendations typically lead to requirements implemented by the IEC. David Lindsay, Southwire's director of distribution engineering is the U.S. delegate to CIGRE study committee B1, which deals with insulated cables.

CIGRE working group B1.25 is reviewing guidelines for design and testing of cables using laminated metallic sheaths at 36 kV and above. In a laminated sheath, a copper or aluminum metallic tape is bonded to a copolymer layer that in turn bonds to a jacket extruded over the cable assembly. The working group's brochure on Advanced Design of Laminated Metallic Coverings is scheduled to be available in late 2009.

"Southwire has wide experience with laminated sheaths, and we are positioned to design and build extruded-dielectric HV cables in compliance with CIGRE recommendations, IEC requirements and all relevant North American standards," says Thomas Wilki, Southwire director of underground high voltage transmission. "We look forward to working with the forthcoming guidelines."

New Standards Define High-Strength Steel Cores
Higher-strength steel core wire allows Southwire to design conductors with higher rated breaking strengths. This means conductors can be installed at higher initial tensions, which reduces operating sag. (NOTE: Southwire engineers caution that increasing installation tension may increase the risk of Aeolian vibration, especially for ACSR conductors.) For 2009, two new standards from the ASTM relate to higher-strength conductor cores:

  • ASTM B957 - 08, Standard Specification for Extra-High-Strength and Ultra-High-Strength Zinc-Coated (Galvanized) Steel Core Wire for Overhead Electrical Conductors, is for core wire used in ACSR and AACSR. "Southwire does not recommend this steel coating in ACSS conductors, because the higher operating temperature of ACSS can deteriorate the zinc coating," says Mark Lancaster, manager of overhead transmission engineering.
  • ASTM B958 - 08, Standard Specification for Extra-High-Strength and Ultra-High-Strength Class A Zinc-5% Aluminum-Mischmetal Alloy-Coated Steel Core Wire for Use in Overhead Electrical Conductors, can be used in several conductor types, including ACSR and ACSS. The Mischmetal coating offers two advantages: it has superior corrosion resistance (better than Class C galvanized) and is stable at much higher operating temperatures than galvanized steel.

"Southwire has offered an ultra-high-strength steel core - HS285 - for several years," Lancaster, who is vice-chairman of the ASTM B01 committee, says. "HS285 delivers an ACSS product with approximately the same strength and installation tensions as traditional ACSR, but with much less sag under thermal loading."

Southwire's standard core wire coating for ACSS conductors is mischmetal, which gives Southwire's ACSS a continuous rating of 250°C - the highest in the industry.

Spacer cable standards will simplify interconnections
Although Covered Aerial Medium Voltage (CAMV) systems have been in use for years under the name of Spacer Cable, there is currently no industry standard for the covered conductors nor for the specialized spacer hardware that carries the conductors. Kim Nuckles, Southwire senior project engineer, is now chair of the Insulated Cable Engineers Association (ICEA) working group on Spacer Cable.

"Industry standards will simplify compatibility and interconnection among components from different manufacturers," says Nuckles. "We started work on a standard for the covered conductors themselves in mid-2008, and we hope to have a reviewed draft ready for acceptance balloting by late 2009. That's good progress. If the balloting goes smoothly, we could have an accepted standard in place by early 2010."