In the world of high-voltage line transmission, advanced reconductoring is getting a second look. These high-temperature, low-sag composite conductors could be a valuable tool in creating a cleaner and higher-capacity grid.

The most common U.S. conductor for power transmission is aluminum conductor steel reinforced (ACSR)—conductive aluminum strands around a steel core. The less common conductors are known as “advanced conductors,” which replace steel for a stronger but smaller composite-based or carbon core. Refined over the last 20 years and counting, these advanced conductors could assist with grid decarbonization that will require higher-­capacity lines to meet vehicle and building electrification, growing gigawatts of alternative power, manufacturing reshoring and more. 

The Electric Power Research Institute (EPRI), Palo Alto, Calif., has been studying advanced conductors, including performing laboratory testing. These advancements include aluminum conductor carbon core (ACCC), aluminum conductor polymer reinforced (ACPR) and stranded composite cores such as aluminum conductor fiber reinforced (ACFR). Sometimes described as propriety conductors, they are in limited use by U.S. utilities. The goal is to get them more readily deployed. While parts of Europe and Southeast Asia have adopted advanced conductors readily, U.S. utilities, state regulators and others may need to learn more before committing more fully. 

The merits

“These advanced conductors can operate at higher temperatures than the majority of conductors that we have on our existing power system,” said Gary Sibilant, EPRI program manager. “Traditional conductors are limited to temperatures of 100°C and lower. Advanced conductors can operate, depending on the type, from 150°C to 250°C.” 

Carbon cores are in the upper temperature range. Higher-­temperature conductors provide more current flow. 

“You can transmit more power down the existing corridor. It’s the power from current and voltage (P = I x V) equation. You increase the current, you increase the power that you can transmit,” he said. 

Another key advantage to developing reconductoring is alluded to in Sibilant’s mention of “power down the existing corridor.” You are replacing existing transmission lines with reconductored ones. 

“You don’t have to get permits for new corridors for your transmission lines. You’re using an existing corridor of which you have all the permits,” he said. 

At most, a utility might need to get a maintenance permit. Such permits are considered routine.

Other benefits of advanced conductors include reduced thermal expansion and conductor weight, and installed tension (notable for carbon and ceramic composite core conductors).

In addition, standards are emerging for advanced conductors. An established standard includes ASTM’s Standard B-987-20, “Standard Specification for Carbon Fiber Thermoset Polymer Matrix Composite Core (CFC) for use in Overhead Electrical Conductors.” Other standards will be needed, Sibilant said.

“Transmission wires have a finite length. You must join lines by connectors, whether regular conductors or advanced conductors,” he said. “We know that the weak point in the system is where the joint occurs. We’re developing connectors standards working with the American National Standards Institute and the National Electrical Manufacturers Association.”

Leading U.S. companies in the manufacture of advanced conductors include 3M with its ACCR, CTC Global’s ACCC, TS Conductor’s aluminum encapsulated carbon core (AECC) and Southwire’s C7. 

Pay now, save later

“Being newer technology, advanced reconductoring can be more expensive upfront,” Sibilant said. “But then you factor the benefits of transmitting more power down existing rights-of-way. As utilities gain more power, they can sell more power. Depending on the conductor, you could be running one-and-a-half to twice the current, expanding capacity where you need it. Such lines also don’t physically expand as much, so they don’t sag or get closer to the ground like traditional lines.” 

That also means less line maintenance (tensioning). There are steel-core lines with fully annealed aluminum strands that can handle higher temperatures, he said, but line sag is a problem.

“At EPRI, we are evaluating the long-term performance of advanced conductors and connectors at our test facility in Charlotte, N.C.” Sibilant said. “We have a test bed where we simulate about 40 years’ worth of electrical and mechanical aging. To validate and ensure their performance, the conductors are put through thermal cycling, heating and cooling while they are under tension. Some of the testing can include weather-related effects such as a core’s performance against fire or atypical temperatures.” 

Advanced conductors using carbon core or composites can nearly double line capacity and create a transmission line that offers far less sag.

Sibilant explained that EPRI testing protocols can become industry standards, citing the example of a performance protocol for line connectors. 

“We’re also developing specifications that utilities can use when purchasing these conductors,” he said. “A project engineer can then ask, did the advanced reconductoring product undergo this testing?”

Transmission capacity 

Zachary Zimmerman is the research and policy manager for Grid Strategies LLC, a power sector consulting firm based in Washington, D.C. Engaged in regulatory and economic analysis, the firm works with a variety of different companies. 

“Studies show that we need to double, maybe triple our transmission capacity over the next 15 to 20 years to meet growing demand,” Zimmerman said. “Advanced reconductoring could play a big role. Lines with advanced conductors could offer advantages in new construction, too. You could reduce the number of towers or have shorter towers associated with these new lines due to the strength of the advanced conductor, which lowers the sag. You also have less power loss.”

Zimmerman added that advanced reconductoring hasn’t typically been considered in transmission planning but a large part that could lie with a need for more education with transmission planners. 

“A switch to a carbon or composite core gives you a lighter line and a smaller core,” he said. “The cores are stronger so you can pack more aluminum on the line. It’s also annealed aluminum, which has more conductivity and is more efficient than hard aluminum. There is a slight upfront price differential between a CSR, CSS and an advanced conductor transmission line, but you must think about the net benefits. When comparing the construction of new transmission line, reconductoring is projected to be at maybe half the cost.”

Zimmerman now sees Southern California Edison as maybe having the biggest plans in terms of using advanced conductors. 

Not a niche application

“Unfortunately, most of the utility industry thinks of advanced reconductoring as a niche application,” Zimmerman said. “Some utilities have adopted advanced conductors, but as a spot solution within certain corridors (e.g., river crossings). For better impact, we need to accelerate its adoption.”

He mentioned that the Inflation Reduction Act and the Infrastructure Investment and Jobs Act are now offering a significant amount of funding that states and utilities can access. That has brought renewed attention to advanced conductors, in part for their potential in handling additional renewable energy for the grid. 

“In this second round of funding, the [U.S. Department of Energy] has placed a big emphasis on new technologies that include advanced reconductoring,” Zimmerman said.

Part of the appeal is the ability to integrate additional amounts of renewable energy through reconductoring. That could help remediate stranded renewable energy that has no on-ramp to the grid. 

“With the need for expanding transmission capacity, advanced reconductoring is a great medium-term solution that can bring additional transmission capacity on much more quickly,” Zimmerman said. “I would add that the new transmission lines that we will still need to build should be done simultaneously with reconductoring existing transmission lines. That way we don’t lose time in the planning, siting and permitting needed for new transmission corridors.”

Recent research

The Energy Institute at Haas, affiliated with the University of California, Berkeley’s Haas School of Business, revised its “Accelerating Transmission Expansion by Using Advanced Conductors in Existing Right-of-Way” in February 2024. The report’s findings, summarized in part, read, “We find that large-scale reconductoring with advanced composite-core conductors can cost-effectively double transmission capacity within existing right-of-way, with limited additional permitting.” 

Using reconductoring in the U.S. power system, the Energy Institute’s modeling showed reconductoring can help meet 80% of new interzonal transmission needed to reach over 90% clean electricity by 2035 (given restrictions on greenfield transmission build-out). 

In efforts to decarbonize the grid, advanced conductors are considered a game changer. Applying advanced reconductoring in existing corridors is, in essence, creating a “new” higher-capacity transmission line at half the cost.

“With $180 billion in system cost savings by 2050, reconductoring presents a cost-effective and time-efficient, yet underutilized, opportunity to accelerate global transmission expansion,” according to the report. “The development of advanced composite-core conductors has opened new possibilities for rapid transmission capacity expansion through reconductoring.”

Additional advantages

The Energy Institute found, through the work of EPRI, the International Council on Large Electric Systems and others, additional advantages of advanced conductors. Varying by conductor model, they included “improved resistance and resilience to bending failure, oxidation, UV waves, galvanic corrosion, and general environmental damage.” 

Advancements were cited, including an embedded optical fiber for real-time monitoring of line temperature and elongation, as well as insulation-based solutions for line wildfire protection.

In the 2024 report, the Energy Institute shared that a Lower Rio Grande Valley reconductoring project in southeastern Texas (American Electric Power) represented the longest advanced reconductored line in the world. The project doubled transmission capacity using CTC Global’s ACCC advanced conductor. AEP needed to address rapid population growth in southeastern Texas and greater-than-modeled seasonal peak demands that led to rolling blackouts during the 2011 south Texas ice storm. The utility did consider new line construction, but the potential of permitting delays and right-of-way acquisition were deterrents to the time-sensitive project.

Zimmerman and Sibilant emphasized that advanced reconductoring, while game changing, should be viewed as one of several initiatives that could be used to help decarbonize the grid. Its timing, however, may be good.

“Utilities are coming around to the fact that we are going to need significant investment in the transmission system to address the changing resource mix, the increase in load, different coming regulations and more,” Zimmerman said. “Advanced reconductoring can help change the game.”