Aluminum Conductor Composite Core
High Temprature Low Sag

What is ACCC® Conductor?

ACCC® conductor (Aluminum Conductor Composite Core) is a high capacity, low sag conductor which consists of a carbon fiber composite core encased in a protective fiberglass sheath that is helically wrapped with conductive aluminum strands. It was developed and patented by CTC Global and ACCC® is a registered trademark of CTC Global. Though CTC Global produces all ACCC® composite cores at its manufacturing facility in Southern California, ACCC® conductor is stranded by its regional conductor manufacturers worldwide. Currently over 30.000 km of ACCC® conductor has been installed at over 340 project sites..

What are the advantages of ACCC® Conductor compared to conventional conductors?

Conventional conductors typically consist of aluminum strands wrapped around steel core wires. The steel core provides strength so supporting structures can be placed further apart. In some cases, steel core wires are not used, but an aluminum alloy is incorporated to improve the strength of the conductor. Special alloys increase electrical resistance which increases line losses. The ACCC® conductor offers several advantages compared to conventional conductors with or without steel reinforcement: The high-strength composite core allows the incorporation of aluminum strands that provide the greatest conductivity (type 1350-O ≥ 63% IACS). Various aluminum alloys can decrease conductivity to ≤ 53% IACS (International Annealed Copper Standard). The composite core’s lighter weight (compared to steel core wire) allows the incorporation of ~28% more aluminum without a weight or diameter penalty (using compact trapezoidal strands). The composite core’s very low coefficient of thermal expansion enables the ACCC® conductor to carry additional electrical current without causing excessive line sag that occurs when conventional conductors heat up under increased electrical load. The ACCC® conductor’s additional aluminum content (and superior conductivity) substantially reduces line losses compared to any other conductor of the same diameter and weight. The ACCC® conductor’s non-metallic core also eliminates magnetic hysteresis losses that can be as high as 6% on 3 layer steel core conductor and 20% or more on single layer steel core conductor under high current conditions. The ACCC® conductor’s composite core is non-corrosive and will not cause a galvanic effect between the core and aluminum strands that can occur with conventional conductors. The ACCC® conductor’s composite core – in conjunction with the smooth surface of the trapezoidal shaped aluminum strands – helps dissipate Aeolian vibration more effectively. The dissipation of vibration allows the conductor to be installed at higher initial tensions often without the use of dampers (based on project specific analysis) which serves to extend the effective service life of the conductor. The high strength, light weight composite core enables installation over long spans which can reduce overall project costs by reducing the number (or height) of the required structures on new transmission or distribution projects. A reduction of structures can often minimize environmental impact, simplify the permitting process, and effectively reduce construction time. The ACCC® conductor’s ability to carry up to twice the current of a conventional conductor makes it ideally suited for increasing the capacity of existing transmission and distribution lines without the need to reinforce or replace existing structures. Higher capacity and reduced sag helps improve the overall reliability of the grid.

Why were composite materials selected for this product?

Carbon & glass fiber hybrid composites offer superior strength to weight ratios (they are much stronger and lighter than steel). Hybrid composite materials do not exhibit the same fatigue failure as metals, nor do they rust, rot, or corrode. Unlike metal alloys, carbon fiber composite materials do not creep over time when subjected to cyclic or continuous high tensile load conditions. They also do not yield (permanently deform) under extreme load conditions. Hybrid carbon and glass fiber composites exhibit elastic behavior and return to their original condition (length) when extreme loads dissipate.

Considering that the ACCC® composite core is elastic, but the fully annealed aluminum strands yield under relatively low strain conditions, what happens to the aluminum strands when a heavy ice or wind load subsequently diminishes?

Following a heavy ice or wind load event (as can be observed in stress-strain testing), the aluminum strands relax around the core which allows the high strength core to carry the majority of the tensile load. While the relaxed strands re-engage under progressively higher tensile load conditions, the advantage of relaxed strands is that the conductor becomes more dimensionally stable under subsequent high current conditions, thereby reducing sag. A secondary advantage is a further improvement in vibration dissipation. Non-ceramic insulators use a fiberglass composite core. Many of these products had problems with “brittle fracture.” Is the ACCC® composite core susceptible to brittle fracture? Several non-ceramic insulator designs (when they were first introduced) utilized a relatively low grade glass fiber that contained boron to reduce manufacturing costs. These products also utilized a relatively low grade resin system that absorbed moisture as the outer silicon / rubber water sheds began to age. Once the sheds aged, moisture was able to wick into the ends of the fiberglass rods, which, when exposed to a highly charged electric field, became acidic. Nitric acid subsequently attacked the boron contained within the glass fibers which caused stress corrosion resulting in brittle fracture. The ACCC® conductor’s carbon and glass fiber core uses a hydrophobic epoxy that resists moisture absorption. Wicking does not occur as core ends are encapsulated very deep within sealed dead-ends and splices, and the glass fibers do NOT contain boron. Extensive testing has confirmed that the ACCC® conductor core is not susceptible to stress corrosion or brittle fracture. Additionally, there is no electric potential to ground (as exists with insulators), so tracking, voltage puncture, and flashover cannot occur. How is the ACCC® core produced? The ACCC® composite core is produced via a pultrusion process where the carbon and glass fibers are impregnated with resin and pulled through a specially heated die to complete curing. The core is made in a continuous process and various lengths are then cut and placed on shipping reels after the entire length has been thoroughly tested.

What types of project applications are ACCC® conductors normally selected for?

The ACCC® conductor was initially developed as a “High Temperature Low Sag” conductor to mitigate thermal sag on transmission lines that were “capacity constrained” due to sag and clearance limitations that occurred when higher electrical currents caused the conductors to heat up and sag due to their high CTE. The ACCC® conductor’s low CTE composite core mitigated thermal sag. It therefore allowed existing transmission lines to be upgraded to carry additional current and is considered to be ideally suited for reconductoring projects. Due to the ACCC® conductor’s increased aluminum content, greater strength, and excellent self-damping characteristics, the ACCC® conductor is now also being utilized on new transmission and distribution lines as it offers increased electrical capacity, decreased line losses, and greater spans between fewer or lower structures. These attributes decrease permitting challenges, simplify tower placement, decrease upfront capital costs, and reduce lifecycle costs. The ACCC® conductors improved efficiency and lower line losses can also decrease fuel consumption and associated GHG emissions.

How does ACCC® compare to conventional conductors?

The ACCC® conductor’s composite core is lighter and stronger than steel or special alloy core which allows the ACCC® conductor to accommodate greater spans, with a lighter more compact design, and also allows approximately 28% more aluminum to be incorporated into any conductor design without a weight or diameter penalty. The added aluminum content decreases electrical resistance, line losses, fuel consumption (or generation requirement) and can help reduce associated emissions. While the ACCC® conductor offers the least amount of thermal sag compared to any other high temperature low sag conductor, the ACCC® conductor offers higher capacity with reduced losses compared to any other conductor available today.

What types of dead-ends and splices are used with ACCC®?

The ACCC® conductor requires specially designed dead-ends and splices. A dead-end assembly consists of a collet housing, collet, and threaded eyebolt. During installation, a lineman removes several inches of the outer aluminum strands to expose the composite core. The collet and collet housing are placed over the core and the threaded eyebolt is inserted into the collet housing (also threaded) and tightened with a pair of crescent wrenches. Tightening the eyebolt into the collet housing tightens the collet and allows it to grip the core. A conventional (though somewhat larger) aluminum sleeve is placed over the conductive aluminum strands and collet / eyebolt assembly and compressed with a conventional 60 ton press using a compression die sized for the particular conductor being installed. The compression sleeve has a jumper pad located adjacent to the eyebolt which allows a jumper to be attached with a standard NEMA four bolt pattern, or other bolt pattern as specified by the customer. Dead-ends are back pressed to prevent conductor bird-caging. Full tension splices contain two collet assemblies that are installed using the same procedure as is used with dead-ends. However, instead of tightening the collets down with the threaded eyebolt ends, a free rotating threaded coupler is used in this case. Once the collet assemblies have been attached and tightened down, a similar outer aluminum sleeve is placed over the collet assemblies and a 60 ton press is used to crimp the ends of the outer sleeve to the aluminum strands on either side of the inner collet assemblies. It is noteworthy that the added mass of dead-ends and splices allows them to operate at approximately one-half of the temperature of the conductor which helps ensure efficiency, performance, reliability, and longevity.

Can “back to back” reels of ACCC® conductor be pulled in with splices preinstalled?

While it is quite easy to pull in back to back reels of ACCC® conductor using back to back Kellum grips or “socks,” we offer specially designed splice that can be pulled in through sheave wheels. Installation crews have successfully pulled in three 12,500 foot reels, in a single pull – which represents over seven continuous miles of conductor. Please contact us for more information.

Can ACCC® conductor be used to upgrade an existing line without deenergizing the circuit?

Quanta Services has successfully reconductored several transmission lines with ACCC® conductor without shutting down the circuits. We can provide more details upon request.

Does ACCC® conductor require dampers?

ACCC® conductor dissipates vibration energy more effectively than conventional round wire conductor designs, so in certain cases dampers may be unnecessary. However, the ACCC® conductor’s greater tensile strength is often utilized to increase spans under higher tensile loads. It is therefore recommended that designers contact us or a damper manufacturer to secure recommendations specific to their project. When dampers are recommended for a specific project the exact location of damper placement is specified. Dampers are generally mounted directly on armor rod.

What type of suspension clamps should be used with ACCC® conductor?

We recommend that AGS Armor Grip® (Preformed Line Products) or similar suspension clamps be utilized. These suspension clamps employ high temperature rated rubber grommets and armor rod. When the angle of the line exceeds 30 degrees, it is recommended that a double suspension clamp be used in conjunction with a yoke plate. Other suspension clamps may be utilized when span lengths, angles, anticipated ice load, and other factors are considered.

How is ACCC® conductor installed? Are there any special requirements?

ACCC® conductor is installed using conventional tools, techniques and equipment. While the installation of ACCC® dead-ends and splices is slightly different than the installation of conventional ACSR, ACSS or AAAC fittings, the conductors are installed in a similar fashion. As with other types of conductors, it is important to follow IEEE 524 installation guidelines and select appropriately sized sheave wheels based on conductor diameter, pulling tension, and angle of the conductor’s entry in / out of the sheave wheels. As with ACSS conductor, ACCC® uses fully annealed aluminum strands that are slightly softer than non-annealed, hardened, or special alloy aluminum. Sheave wheels should be properly aligned so that scuffing of the aluminum strands does not occur and the conductor should not be dragged across the ground that could damage the aluminum strands and induce corona on an energized line. Additionally, as the ACCC® conductor’s composite core is essentially non-conductive, care must be exercised such that grounding clamps are placed directly on the aluminum strands.

Is there any advantage to pre-tensioning ACCC® conductor during installation?

Pre-tensioning ACCC® conductor can lower the conductor’s thermal kneepoint to further reduce thermal sag and quickly create an “after load” stable sag and tension condition. The thermal knee point is essentially the apex of the transition period when the aluminum strands thermally expand and relax to the point that they no longer carry any tensile load and all load is then carried by the very dimensionally stable and very strong composite core. While the conductive aluminum used for ACCC® conductor yields under very little load, pre-tensioning can be done with very little effort in a very short period of time. Typically ACCC® conductors are installed at 15 to 25% of their Rated Tensile Strength. Pre-tensioning the conductor by as little as 5 to 10% for a matter of 30 minutes can effectively relax the aluminum strands such that they no longer carry significant (or very little) tension under normal load conditions. However, should an extremely heavy ice or wind load condition occur in the future, the aluminum strands will reengage which increases the conductor’s overall tensile strength and resistance to sag. Pretension also improves the conductor’s self-damping as well as its fatigue resistance, and should be considered when permissible.

Is the ACCC® composite core flexible?

The ACCC® composite core is extremely flexible, but retains kinetic energy when bent, much like a fiberglass fishing pole. Like a fishing pole, the ACCC® core exhibits a shape memory characteristic and prefers to be straight. While this characteristic makes it very easy to handle during installation, if the ACCC® conductor is bent in a sharp angle (i.e., not around a radius), damage to the aluminum strands or core may occur. Care should be taken so this does not happen. To better understand the ACCC® conductor’s bending limitations AEP performed a simple bend test on a Drake size ACCC conductor; after being bent 10 times around a 6 inch (15 cm) radius conduit pipe bender, the only degradation noted to the 3/8 inch (9.5 mm) core was a 20 micron hole within the outer fiberglass shell as identified using fluorescent dye penetrant.

Can the ACCC® conductor be used on long spans or on spans subjected to heavy ice loads?

A vast array of ACCC® conductor sizes and designs are offered to accommodate a wide range of applications. While extreme span conductor designs are highly specialized, heavy ice load designs fall within the standard product line.

The ACCC® conductor’s core is made with carbon fiber surrounded by glass fiber. Why is the core not all carbon fiber?

The carbon fiber is surrounded with glass fiber to improve flexibility and toughness, and provide a durable protective layer to prevent galvanic coupling between the carbon fiber and aluminum strands. Galvanic coupling can happen if the aluminum strands are in “direct and substantial physical contact in the presence of an electrolyte within a certain pH range,” so even if the outer glass layer was damaged or cracked, it would be difficult to create direct and substantial physical contact between the aluminum strands and central carbon fiber core. Glass fibers as used in numerous aerospace applications for the same purpose due to their resistance to wear compared to other coatings.

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