The differences between 3M ACCR and other conductors are due to differences in materials. 3M ACCR's core wire is composed of all aluminum-based components. In addition, it uses a high temperature, hardened aluminum zirconium for the outer wires. This material combination offers two main advantages over other high temp, low sag conductors – ampacity and durability.
High temp, low sag conductors that rely on steel or other metals such as nickel alloy are heavier than the same diameter 3M ACCR. Therefore, even when sag performance is improved, the same capacity cannot usually be gained without compromise – rebuilding or raising towers, installing taller towers, increasing the tension, or, in some cases, putting up a smaller conductor under higher tension, which increases losses. Therefore, 3M ACCR offers the maximum capacity increase without adding the risk of modifying the structures, often reducing siting and permitting requirements.
Conductors relying on carbon polymers as the core material may not have comparable durability. Thermoset matrices are more prone to degradation if exposed to heat, ultra-violet rays (sun) or moisture, as found both by 3M and other researchers. Testing performed in the U.S. and China indicates that the core starts to degrade and show permanent deformations at temperatures as low as 150° C. At 170° C strength is reduced, and some of the reduction may be irreversible.1
Testing in the U.S. also showed mechanical failure at tensions as low as 93% of rated breaking strength, as well as under excessive bending. As a result, the maximum recommended tension loading may be as low as 80% of the catalog RBS.2 Known failures of these conductors either during installation or operation have occurred in the U.S., China, Poland, South Africa and Indonesia.
Carbon composite conductors using thermoplastic as the core matrix rely on a material with a glass transition temperature between 85 and 100° C, close to the temperature rating of ACSR. The glass transition temperature (Tg) is the temperature at which polymers transition from a hard state into a molten or rubber-like state. The impacts of a low Tg on high temperature operations of the conductor are not fully understood.3
Some high temp, low sag conductors achieve their sag performance by using a softened, or annealed, aluminum for the conductor outer wires. However, softened aluminum is harder to handle during installation and is more prone to damage than a hardened aluminum, such as used in 3M ACCR. Replacing hardened aluminum with softened aluminum also yields a loss of strength. Galvanic corrosion can be a problem if aluminum is used with materials that contain steel or carbon. Coatings or barriers are required to prevent corrosion. However, because 3M ACCR is all-aluminum-based, it is corrosion resistant without barriers that can be damaged during handling or installation.
Therefore, 3M ACCR is the only conductor on the market with its unique blend of sag and capacity performance and durability, resulting in more than a decade of reliable, successful installations. And it is the only conductor supported and backed by 3M, a company doing business for over 100 years, more than 60 in the utility industry.
3M believes that 3M ACCR is substantially similar to the competitive products on the basis of form, fit and function. Please see 3M product specifications for detailed product information. All data presented here is based on publicly available information compiled from respective manufacturers as of September 2014 and is believed to be reliable, but the accuracy or completeness is not guaranteed.
As always, before using the 3M product, you must evaluate it and determine if it is suitable for your intended application.
1See Electric Power Research Institute, "Aging Assessment of a Composite Core High-Temperature Low Sag (HTLS) Conductor," February 11, 2009. See Also Leveque, David, Anne Schieffer, Anne Mavel and Jean-Francois Maire, "Analysis of How Thermal Aging Affects the Long-term Mechanical Behavior and Strength of Polymer-matrix Composites," Composites Science and Technology, Volume 65, Isssues 3-4, March 2005, pp 395-401. See also, Kumar, Bhavesh G., Raman P. Sing and Toshio Nakamura, "Degradation of Carbon Fiber-reinforced Epoxy Composites by Ultraviolet Radiation and Condensation", Journal of Composite Materials, pp. 2713-2733, Vol. 36, No. 24, 2002. See also, Burks, B.M., D.L. Armentrout, M. Baldwin, J. Buckley, M. Kumosa, "Hybrid Composite Rods Subjected to Excessive Bending Loads," Composites Science and Technology, 69, 2009, p. 2625-2632. See also Li, Rui, Hon-yun Yu, Chang-shui Yu and Jun Cao, "Some Questions Should be Paid Attention on ACCC Application", Electrical Equipment, Volume 9, No. 5, May 2008.
2See Freimark, Bruce, et. al., "Sequential Mechanical Testing of Conductor Designs," 2009 Electrical and Substation Structures Conference, IEEE, November 8-12, 2009.
3Fortron® Design Manual FN-10, Ticona, 1999