How Nation’s Largest Dynamic Line Rating Deployment Unlocked Nearly 50% More Transmission Capacity for Great River Energy

Great River Energy’s dynamic line rating (DLR) project is the largest DLR deployment to date in the U.S. based on the number of sensors installed. Early results identified a 48.92% increase in power carrying capacity on one of the monitored lines. These facts, and more, make the project worthy of recognition as POWER’s 2025 T&D Award winner.

Traditional power line ratings, known as static thermal ratings, are based on conservative worst-case weather assumptions—typically high ambient temperatures, low wind speeds, and maximum solar heating. While this approach ensures safety, it significantly underutilizes transmission capacity for the majority of operating hours.

Dynamic line rating (DLR) technology offers a transformative solution by continuously monitoring actual weather conditions and conductor temperatures to determine real-time transmission capacity. By accounting for factors like wind speed, ambient temperature, and solar irradiance as they actually occur, rather than assuming worst-case scenarios, DLR can safely increase line capacity by 10% to 40% on average, with even higher gains during favorable weather conditions. For grid operators facing the dual pressures of decarbonization and reliability, DLR represents a cost-effective bridge solution that maximizes existing infrastructure while longer-term transmission expansion projects advance through planning, permitting, and constructing processes.

Great River Energy’s DLR Pilot Project

One location where weather can be quite volatile is in Minnesota. The state has well-tapped wind and solar resources, particularly in the west, but the variability of these renewable sources presented a challenge for Great River Energy, a not-for-profit wholesale electric power cooperative based in Maple Grove, Minnesota, serving 26 member-owner distribution cooperatives, supplying electricity to about 1.7 million people. “We believed that DLR could help us manage all that volatility and offer us a way to get additional capacity sooner while evaluating infrastructure upgrades,” Michael Craig, manager of Energy and Distribution Management Systems with Great River Energy, told POWER.

While Great River Energy’s transmission system is built and designed to handle the generation and load that is on it, the grid is becoming more dynamic with wind and solar generation still being added, along with data centers and other loads. Planned and unplanned outages can also add complexity, all of which can cause congestion on the system. With this as a backdrop, the cooperative embarked on a mission to assess the benefits of DLR.

Most utilities, including Great River Energy, are aware of congestion bottlenecks in their grid because those areas often require a lot of attention. With this understanding, Great River Energy easily identified a pilot line that it felt would be useful for its DLR evaluation. “The pilot line was selected because it was fairly straightforward, and we knew it would allow us to generate the data we needed to quickly validate—or debunk—our theory that DLR could be the right solution,” said Craig.

To begin the pilot program, in September 2023, Great River Energy technicians used hot sticks (live-line tools) to install four Neurons (see opening image). “The Neuron is a collection of sensors packed in an eight-pound sphere that is about the diameter of a small soccer ball. It opens like a Pac-Man for installation directly onto powered high-voltage transmission lines—from 7 kV to 550 kV—to monitor critical parameters including conductor temperature, current, sag, phase angle, ice buildup, and environmental conditions, like wind and humidity,” Tom Cleaver, vice president of North American markets with Heimdall Power, explained.

Great River Energy’s approach was almost entirely results driven, according to Craig. By March 2024—just six months into the pilot—Great River Energy was seeing such great results that it was ready to scale up. “The data was irrefutable. DLR opened an additional 48.92% capacity in our pilot transmission line, which made the decision to scale a no-brainer,” said Craig.

“Our initial goals were to increase transmission capacity in ways that were faster, less costly, and easier than building new infrastructure or reconductoring,” recalled Craig. “We moved from pilot to full deployment in less than nine months. This is really fast by industry standards, but the initial results were so compelling, especially when compared to the investment required. Also, having sensors installed on these lines didn’t stop us from doing congestion analysis and system planning, so we were—and always are—doing that work in parallel to identify areas that could need investment.”

Deploying DLR at Scale

After Great River Energy’s initial identification of congested lines, Heimdall Power conducted a more thorough line study to determine optimal Neuron placement along each line span. Strategic sensor positioning is essential to ensuring that the resulting data accounts for all the variables along a line span. Factors such as elevation change and surrounding foliage along a span can impact the real-time conditions, and thus, the capacity of a line.

“Heading into the pilot, we had already identified the additional lines we would target if the pilot proved to be successful, because we don’t pilot for the sake of piloting, we design pilots to fast-track a full deployment if the value is there,” said Craig.

From the beginning, Great River Energy’s plan had been to install all of the DLR equipment on its own using the hot stick technique, but nature had another plan. “We found ourselves on the tail end of a really wet spring season,” Craig recollected. “Installing by hot stick would have required additional labor, machine hours, and matting simply to access the selected spans. Even then, heavy trucks could have had difficulty getting in and around the selected spans.”

The team had a few choices. They could have spent extra money to extend work hours and manage field conditions to install by hot stick on the original schedule or they could have delayed deployment until the conditions improved and the ground dried up. But what emerged as the best option was using drones to do the work. “It was an easy decision,” said Craig.

In the end, 80% of the physical Neurons (40 of 50) were installed by Heimdall Power onto live lines using drones (Figure 1). The other 20% (10 physical Neurons, including the four that were part of the one-line pilot) were installed by Great River Energy’s technicians using hot sticks. Now, a total of 10 lines are being monitored—eight by 50 physical Neurons and two by 37 virtual Neurons.

1. The Neuron can be installed on powered lines using a drone. Neurons monitor key parameters directly on the line, providing users with real-time data. Courtesy: Heimdall Power

“Virtual Neurons are software-based sensors that can be deployed instantaneously, either alone or with physical Neurons, to monitor grid capacity by combining line weather data and historical DLR data,” Cleaver explained. “In practical terms, the two solutions complement one another and extend the value of each. Virtual Neurons are continuously trained with data from the physical ones to incrementally improve accuracy and forecasting over time, a feat that is impossible without real-time data from the power line itself, which is provided by the physical Neurons.”

Cleaver noted that virtual Neurons can be used alone to achieve Federal Energy Regulatory Commission (FERC) Order 881 compliance, but Great River Energy is using them in a hybrid configuration with physical Neurons to cover more of their grid in a cost-effective way. This approach also offers users the flexibility to re-deploy anywhere, anytime, enabling them to pivot quickly to capture real-time data when and where it’s most needed.

“From Heimdall Power’s perspective, software-based DLR, which is one capability our virtual Neuron can deliver, has its place in the future of grid monitoring. However, it can’t be the only thing. It should be part of a dynamic mix of tools and inputs that must include physical, real-time data from the line,” said Cleaver.

Other Considerations

While DLR is clearly a great tool for increasing power line capacity utilization, there are other factors that can cause congestion. For example, Great River Energy’s pilot line was rated at 142 MVA per its summer seasonal line rating. During the 2024 summer season, Great River Energy was theoretically able to increase capacity on the line by 48.92%. If fully realized, these gains would have boosted the line’s overall transmission capacity to an average of 211 MVA.

However, that potential is based on the transmission line/conductor only and does not factor in the next-most-limiting element in the transmission system, which could include anything from jumpers to circuit breakers. In the case of Great River Energy’s pilot line, the next-most-limiting element was rated at 173 MVA. Therefore, the realized gains were capped at 173 MVA. Still, having this information is important and can help prioritize upgrades in other areas of the system.

“This dynamic scenario is unique for each line, and for Great River Energy, varies based on its summer and winter seasonal ratings. And because heat is the most impactful variable in determining transmission line capacity—the hotter the line, the lower the capacity—summer line ratings are typically much lower than winter seasonal line ratings,” Cleaver explained. “As is true for most utilities, the summer season is when DLR is most critical. As temperatures rise so do congestion events and power outages. So, while winter ratings are helpful, summer ratings are likely a better indication of where DLR can really add value.”

It is also worth noting that approximately 2% to 3% of the time, Great River Energy’s summer seasonal ratings are higher than DLR. While gains are good, there is also value is having a true and accurate understanding of line conditions, rather than hoping calculated worst-case conditions adequately protect lines.

“There is no getting around the fact that we will need to build new infrastructure or reconductor at some point, but we knew that DLR could allow us to defer those investments, or space them out over a longer period of time. We also knew that once that new infrastructure did come online, DLR could complement those new systems, too,” Craig concluded.

—Aaron Larson is POWER’s executive editor.