Celanese Corp. (Dallas, Texas, USA) and Southwire Co. LLC (Carrollton, Ga., USA), North America’s largest wire and cable producer, have introduced a new option for utility transmission lines, the C7 Overhead Conductor, featuring a multi-stranded composite core of Celstran continuous fiber-reinforced thermoplastic rods (CFR-TPR) from Celanese.
The Celanese- and Southwire-developed transmission conductor delivers nearly double the capacity and exhibits less sag than the same diameter aluminum conductor steel-reinforced (ACSR) conductor. The design using high performance thermoplastic composites allows for minimum thermal and mechanical sag at higher power transfer, and the stranded Celstran CFR-TPR core means there is no single point of failure for the overhead conductor.
Mark Lancaster, director of overhead transmission engineering at Southwire, says the technology behind C7 was more than six years in the making and represents a step-change in overhead wire and cable design and engineering. The goal, he says, was to develop a product for utilities looking to increase right-of-way capacity without the expense of erecting new infrastructure. Line sag, he says, is the largest limiting factor in how much current can be passed through a utility line. "We wanted to increase capacity of the right of way over the same equipment." The result is a product that not only increases capacity, but provides cost-avoidance benefits by obviating the need for new towers and poles — as might be normally expected with traditional lines. In addition to new installations, the C7 conductor offers performance benefits and a strong value proposition for re-conductoring applications as well, allowing for higher performance and emergency service rating of lines.
The C7 Overhead Conductor comes in a variety of constructions using Al-Zr and O-Temper Aluminum. One standard configuration uses seven 3.2-mm/0.13-inch diameter strands (or more, depending on cable diameter) of aerospace-grade carbon fiber composite. Each strand is pultruded with a matrix of Fortron PPS from Celanese and then capped with a layer of PEEK material to provide protection from galvanic corrosion and a high abrasion resistance. The bundled strands, overwrapped by Southwire with an aluminum conductor, provide a redundancy of structural support in high-load conditions. In addition, notes Lancaster, the carbon fiber core operates at a generally lower temperature, which maximizes energy throughput and minimizes capacity loss. On top of that, the thermoplastic carbon fiber composite strands from Celanese can operate at high temperatures without damaging the line.
Finally, notes Lancaster, C7's success as a replacement products depends on the ability of line installers to use the same tools and equipment as they would with a cable made with traditional material. "Install and repair strategies had to be the same," he says, "so that our customers can seamlessly integrate it into their work environment."
The C7 Overhead Conductor provides seven key advantages:
- Minimal thermal expansion — Lowest level available in a composite core for minimal sag increase at high power transfer
- Light weight — High strength-to-weight ratio
- Multi-element core — No single point of failure, unlike monolithic constructs
- Flexible and robust — Installs like traditional conductor without the need for special training and equipment
- Celanese engineered material — The only all-thermoplastic composite core in the world, with high-temperature performance (180°C to 225°C)
- Multiple conductor designs — Tailored for installation requirements, from light to heavy ice loads, normal to long spans, and numerous conductor constructions
- Use of conventional connectors — Traditional, crew-friendly, two-piece compression fittings
“Designed for utilities that want greater flexibility, reliability and ease of installation, the C7 Overhead Conductor uses Celstran CFR-TPR composite technology that involves an innovative combination of carbon fiber and a heat-resistant Fortron PPS [polyphenylene sulfide] matrix that is capped with a layer of high-performance PEEK [polyetheretherketone],” says Michael Ruby, global composites business manager at Celanese. “This combination of materials provides distinct performance and lifecycle economic advantages compared to alternative High Temperature Low Sag (HTLS) technology and conventional conductors.”
“Southwire has a 60-year history of quality and innovation when it comes to supplying utilities with transmission solutions,” says Lancaster. “Our goal in creating the Southwire C7 Overhead Conductor was to give customers an alternative to our standard ACSR and HS285 transmission line solutions that offered flexibility, reliability and ruggedness to stand up to a variety of difficult environments.”