Unlocking the Grid with Advanced Transmission Technologies (ATT)

Advanced Transmission Technologies (ATTs) are infrastructure, hardware, and software options that cost-effectively increase the capacity and resilience of the transmission grid. While these technologies have been commercialized and have an established track record, they are not yet default solutions considered by most U.S. transmission owners. ATTs can be broken out into three broad categories including: (1) Grid Enhancing Technologies; (2) High-Performance Conductors; and (3) Other ATTs.

Grid-Enhancing Technologies (GETs)

GETs are hardware and/or software that dynamically increase the capacity, efficiency, reliability, and/or safety of existing power lines. These technologies are installed faster and at a lower cost than greenfield transmission development.

From…
Legacy Solutions
Used since 1900s

Historically, utilities have used one set of assumptions for how fast the line is heated by the power flowing through it and the heat is spread to the air to determine the capacity of the transmission line, known as static line ratings. By summer 2025, utilities are required to use forecasted temperature to adjust the static rating for each line.

Power flow control (PFC) solutions have been available for decades, from series reactors and series capacitors to Phase Shifting Transformers. However traditional PFC solutions must be custom-built, have long lead and delivery times, and require considerable substation space which all drives significant solution cost. Additionally, these solutions were designed to control large volumes of power flows, and do not provide the dynamic real-time control required for today’s grid.

In the past, grid operators have managed reconfigurations manually. Sometimes grid operators develop “Remedial Action Plans” and “Operating Guides” that include reconfigurations to address specific scenarios such as line outages. However, operators and planners usually don’t systematically look at reconfigurations to reduce system costs because it has been too time-consuming and difficult.

To…
Advanced Transmission Technologies
Commercialized since 2000s

Dynamic Line Ratings (DLR) use sensors, software, or both, to measure environmental factors or line behavior to forecast and calculate the true transmission capacity. For example, today’s line ratings often assume a wind speed of 2 feet per second (barely a breeze), but the average wind speed across most of the US is over 10 ft per second at the height of transmission lines, which means that the lines are typically cooler than assumed and can safely transmit more power. The benefits of DLRs are:

• Boosts line capacity by at least 10% for almost 90% of the time.

• Increases capacity by an average of 30-50% with favorable climate and geography.

Advanced Power Flow Control (APFC) refers to power electronic-based devices that can actively change the way power flows through the transmission system, providing dynamic control to push power off overloaded circuits or pull power onto underutilized lines. APFC is designed to be a modular, voltage-agnostic, cost-efficient solution as more APFC devices can be easily and quickly added to existing deployments over time or relocated between sites. The primary advantages of APFC are:

• Ease congestion or mitigate an outage by redirecting power flows.

• Improved grid stability by controlling voltage.

• Modular, smaller designs, which enable scaling or redeployment.

Topology Optimization software can operate as the grid’s navigation app – when there’s too much traffic on one power line, it can find alternative, reliable routes for the power. Available power sources, where power is needed, and the status of grid infrastructure all feed into the software to determine the best use of the network based on available switches and reroute power around bottlenecks. Often, those changes are not intuitive, and this sophisticated software allows grid operators to identify and test reconfigurations quickly. Topology Optimization can:

• Use reconfigurations to reduce congestion or mitigate outages.

High-Performance Conductors (HPCs)

HPCs are modern conductor technologies that have greater performance characteristics when compared to traditional aluminum-conductor steel-reinforced (ACSR) conductors, including increased capacity, higher efficiency, and lower thermal sag.

From…
Legacy Solutions
Used since 1900s

Aluminum-conductor steel-reinforced (ACSR) conductors have been and generally still are the default conductor choice for the grid. In the 1970s a new type of conductor called aluminum-conductor steel-supported (ACSS) conductors was developed and is increasingly used today. For both conductors, the electricity flows through the aluminum conductor and heats the line over time because of resistance in the metal. The steel core keeps the line strong, but with enough heat it will soften and start to sag. This limits how much electricity can be transmitted safely and without damaging the power line.

To…
Advanced Transmission Technologies
Commercialized since 2000s

Carbon/Composite Core Conductors, also known as Advanced Conductors or High-Temperature Low-Sag Conductors, are overhead, bare conductors that use a trapezoid-shaped wire of annealed aluminum to carry electrical current and use a carbon or composite core for support. The conductors have been used commercially for 20 years and are deployed in over 60 countries across five continents. Carbon and composite core conductors have three key advantages over traditional ACSR and ACSS conductors:

• Can double the capacity of the transmission line.

• 30% or more efficient.

• 50% less sag.

Superconductors use a class of metallic compounds that exhibit negligible resistance when cooled using liquid nitrogen, enabling very low losses and high power-flow capacities. High-temperature superconductors were developed in the 1980s and have been installed in Europe, Asia, and the U.S. over the past 20 years. Superconductors have four key advantages over traditional ACSR conductors:

• Five-fold increase in capacity for Alternating Current and 10 times for Direct Current.

• No thermal sag or underground deployment.

• At least 50% more energy efficient than ACSR conductors.

• Can transfer high capacity at lower voltages avoiding substation build and costs.

Other ATTs

Other ATTs includes Storage-as-transmission (i.e., Battery Energy Storage Systems), which is an ATT solution that falls outside of the first two categories. Note that this category is non-exhaustive.

To…
Advanced Transmission Technologies
Commercialized since 2000s

Storage as Transmission are batteries within the grid which can defer or offset transmission capacity expansion, support peak load management, and/or provide other grid services to enhance system resilience and reliability. Batteries can help control power flow or shift power flows over time by storing power on either side of the transmission line to deliver later. The benefits of storage-as-transmission include:

• Providing incremental and faster solutions to changes in power flows or mitigation of congestion.

• Providing a more efficient or cost-effective transmission solution, or bridge service helping to maintain reliability while larger upgrades are under construction.

• Supporting reliable grid operation through ancillary services that maintain voltage and frequency at a lower cost than transmission or generation additions.

From…
Legacy Solutions
Used since 1900s

Traditionally, expanding the capacity of the grid to deliver power would entail building a new transmission line, upgrading an existing line or adding generation to provide the needed ancillary benefits, such as voltage support.