With all of the recent discussion around “HTLS conductor” & “advanced reconductoring”, it is more important than ever to understand/properly define the different types of overhead conductor technologies in existence today.
Steel core conductor has been the go-to solution for electric utilities for many years now. ACSR was invented over 100 years ago & ACSS over 50, and while they still have a place within utility networks, composite core or “advanced” conductors will forever change the way utilities approach the need for a more capable and dependable grid.
There is a reason the most demanding applications have relied on carbon fiber composites (aerospace, military, and medical to name a few). These materials have an intrinsically low coefficient of thermal expansion (roughly 10x lower than conventional steel) and impressive specific properties in tension (twice as strong as steel for 1/4 of the density). These attributes make composites ideally suited to perform as the strength member for overhead conductor within transmission and distribution networks.
The thermal properties/strength-to-weight ratio of composite conductor core allows for twice the current carrying capacity of conventional steel core conductors and an added ~28% more aluminum content, the conductive substance, without a weight or overall diameter penalty. They are also installed using industry standard guidelines (IEEE-524) & equipment.
Below is an overview of the four technologies that exist today.
Carbon/Glass Fiber Hybrid
- Design Concept: The carbon/glass hybrid design combines the mechanical advantages of carbon fibers with the flexibility and cost-effectiveness of glass fibers. This approach delivers a balanced solution suitable for most field conditions, offering a strong cost-to-capacity ratio that has made it the most widely deployed composite core technology worldwide.
- Versatility: Hybrid cores can be tailored to meet specific operational requirements by adjusting fiber types or matrix materials. These adjustments allow for a range of performance capabilities, including varying ampacity and mechanical strengths. This adaptability has been a key factor in its broad adoption and consistent performance.
- Proven Track Record: With over a decade of qualification through ASTM B987, this technology has established itself as a reliable and trusted solution for utilities seeking to improve grid capacity and efficiency. Manufacturers like Epsilon Composite have developed highly versatile offerings in this category, supporting both standard and customized applications.
All Carbon Fiber with Aluminum Encapsulation
- Design Concept: This solution incorporates carbon fiber cores encased in aluminum, providing a higher elastic modulus compared to hybrid designs. Its mechanical rigidity makes it particularly effective in mitigating sag caused by radial ice loads, making it well-suited for cold climates.
- Thermal Considerations: To maintain optimal performance, these cores are designed for operating temperatures below 160°C, as higher temperatures can result in epoxy resin off-gassing. This off-gassing can compromise the aluminum encapsulation and reduce galvanic corrosion protection. Attention to material quality is critical, as lower-grade products have exhibited off-gassing at even lower temperatures.
- Applications: As a complementary solution to hybrid designs, this technology excels in environments where mechanical rigidity is prioritized over thermal constraints. Epsilon Composite has successfully deployed this design in various projects, offering reliable performance tailored to specific regional and climatic needs.
Multi-Strand Composite Core
- Design Concept: Multi-strand composite cores consist of several carbon fiber strands coated with galvanic protection layers. This design provides some level of load-path redundancy and offers a familiar, stranded appearance similar to traditional metallic cores, making it more intuitive for some field applications.
- Performance Challenges: A significant consideration for this design is the risk of damage caused by increased stress or abrasion at the interface of the strands. Due to small points of contact between strands, high localized pressure can lead to wear, structural degradation, or reduced reliability over time, especially in demanding operational conditions.
- Structural Considerations: Often referred to as a "black metal design," this approach essentially replicates metallic conductor concepts without fully optimizing the structural advantages of composite materials. While the multi-strand layout offers flexibility, it may sacrifice axial tensile strength and long-term durability due to off-axis fiber orientation and internal abrasion risks.
Metal Matrix Composite
- Design Concept: Metal matrix composites consist of alumina fibers embedded in an aluminum matrix, resulting in a unique material that offers slightly higher thermal ratings compared to polymer matrix composites.
- Performance Challenges: The key drawback of this technology lies in its structural fragility. The homogeneity of the metal matrix design can lead to failure under stress, particularly during installation or in high-tension applications. Numerous incidents of breaking conductors have been reported, underscoring the need for careful handling and installation procedures.
- Economic Constraints: Beyond fragility, the cost of metal matrix composites is often cited as a limiting factor. At approximately twice the cost of polymer matrix equivalents, these materials are challenging to justify for widespread deployment without significant performance improvements.
- Applications: While promising for niche scenarios where thermal capabilities are paramount, these composites face practical barriers due to fragility and high CAPEX requirements.
Conclusion
Advanced conductor technologies are reshaping the future of energy transmission, offering utilities new ways to enhance grid performance while meeting increasing demands for reliability and efficiency. Each solution brings unique advantages and considerations, requiring thoughtful evaluation to match the right technology to specific project needs.
By fostering dialogue and collaboration, the industry can continue advancing toward a more capable and resilient grid.