Dynamic Line Ratings: An Innovative Tool for Increasing Grid Capacity

Dynamic Line Ratings (DLR) are an innovative approach to operating transmission lines that allow electric utilities to utilize the true maximum safe capacity that can be transmitted through the lines (ampacity). Carrying more power on existing infrastructure allows utilities to save on transmission upgrades, reduce congestion, and ultimately save consumers money.

DLR is made possible by different methodologies that measure the various properties in the field such as ambient weather conditions and temperature of the conductors on a transmission line. Data on conductor conditions and the surrounding environment are collected and used to calculate the DLR for the line.

DLR has the potential to significantly improve the efficiency and reliability of the power grid. Implementations of the technology require no new construction and can be operational and provide benefits to the grid in months. As the electricity demand continues to grow from electrification, DLR will be an important piece of the puzzle for operators to adequately meet demand.

History of DLR

DLR is an established technology that has been around for longer than you may have thought. The first research on DLR was conducted in the 1990s. This research was focused on developing methods for calculating the thermal rating of transmission lines based on real-time weather conditions.

The first pilot projects for DLR were conducted in the early 2000s. These projects successfully demonstrated the potential benefits of DLR, leading to the development of commercial DLR systems in the mid-2000s. DLR technology has continued to mature in recent years aided by sophistication in hardware and software and is now being deployed by utilities around the world.

Line Ratings

To break down DLR, we first need to examine the principles of a conductor. All transmission lines have a thermal limit (maximum operating temperature) that determines the amount of power that can flow through the conductor.

The conductor is heated from power loading on the line and solar radiation. At the same time, the line can be cooled by the ambient air, wind, and radiative cooling. As the conductors heat up, the metal expands causing them to sag, becoming closer to the ground. As conductors cool down, they contract and return to their original position. Too much sag can result in the conductor coming into contact with vegetation or other objects, becoming damaged, failing, or sparking a wildfire.

Line ratings are thus used to prevent the damage and failure of transmission lines. The current standard method to determine the limit of a line is to use conservative assumptions about a line’s conductor type, average weather conditions, wind speed/direction, ambient temperatures, and solar conditions for summer and winter. These standard ratings are called Static Line Ratings (SLR). These ratings generally prevent failures of transmission systems, but are static in nature, meaning that they do not account for changes in the environmental conditions except on a seasonal basis.

Mixing a static assumption with a dynamic environment can lead to issues and deficiencies. SLRs tend to leave an unnecessarily wide berth when the weather is cool, the solar radiation is low, or the wind is higher than expected, leaving essential grid capacity unused. Other times, SLRs can overestimate a line’s capacity in times of low wind, high solar intensity, and high ambient temperatures, increasing the risk of excessive sag or damage.

Two different types of ratings address these issues — Ambient Adjusted Ratings and Dynamic Line Ratings.

Ambient-Adjusted Ratings (AARs) are often adjusted daily or hourly using ambient temperature weather modeling but still make assumptions about local wind speeds. They are calculated with the following variables:

• Ambient temperature
• Presence of Solar Radiation
• Conductor Properties, Emissivity, and Absorptivity
• Conductor Maximum Operating Temperature

Dynamic line ratings use field-monitored data and represent the true line rating — making no assumptions. They use sensors to collect real-time data about the conductor temperature, sag, and the contributing factors to conductor conditions; air temperature, solar radiation, and wind speed and direction on the transmission line. Armed with this crucial information grid operators can utilize the additional capacity to optimize system operations.

There are a number of different methods for calculating DLR. Some of the most common methods include:

• Thermal monitoring: This method uses sensors to measure the temperature of the conductors on a transmission line. The data from the sensors is then used to calculate the dynamic line rating for the line.
• Thermal modeling: This method uses a computer model to simulate the thermal behavior of a transmission line. The model takes into account the weather conditions, the conductor type, and the line configuration.
• Hybrid methods: These methods combine thermal monitoring and thermal modeling. This allows for more accurate and reliable dynamic line ratings.

The Difference:

While they sound similar, DLR and AAR work differently.

DLR is more accurate — Under DLR approaches, the use of real-time weather and wind speed data (beyond the ambient temperature data used in AAR approaches) allows DLRs to even more accurately reflect transfer capability.

DLR can occasionally be lower (safer) than AAR — DLRs will occasionally identify that the near-term weather and/or other conditions are actually more extreme than the assumptions under other methodologies, and will therefore result in a line rating that is lower than a static, seasonal, or AAR rating would have allowed. Sometimes less is more — DLR’s additional data inputs avoid overstated ratings, reducing operational risk.

Deploying DLR sensors brings additional benefits — DLR improves operational and situational awareness by helping transmission operators to better understand real-time transmission line conditions and potential anomalies, such as possible clearance violations. Sensor-validated DLR allows an extra layer of protection, accuracy, and deep learning, compared to software-only models.

Current usage of DLR

DLR is a widely-accepted tool, validated by organizing bodies such as IEEE and CIGRE. DLR is currently being installed around the world — according to the WATT Coalition, DLR has been installed in at least 12 countries, with more being added each year.

DLR has been proven to alleviate several problems the modern grid is facing, including:

• Increasing the capacity of new and existing transmission lines
• Reducing congestion on the power grid, saving consumers money
• Improving the reliability of power supplies
• Integrating renewable energy sources into the grid
• Incorporating Commercial & Industrial load growth

Read more: This MIT Study simulated Dynamic Line Ratings across the ERCOT Grid, the results were impressive

The Impacts of DLR

DLR has the potential to have a significant impact on the power grid. By increasing the capacity of transmission lines by up to 40%, DLR can help to reduce congestion on the grid and improve the reliability of power supplies.

DLR can also help to integrate renewable energy sources into the grid by adding additional capacity, which is important as the demand for renewable energy continues to grow. DLR is particularly compatible with wind energy, as there is a relationship to wind speeds, turbine output, and the cooling of conductors — when the wind blows, wind farms are more likely to be curtailed, but can be mitigated by higher line ratings during the wind. Additionally, DLR can occasionally be lower than SLR, which allows grid operators to avoid thermal damage to lines and incidents associated with too much sag

Overall, DLR is a technology that has the potential to significantly improve the capacity and reliability of the power grid. Dynamic Line Ratings are an essential piece of the puzzle when it comes to increasing the capacity of the transmission system to enable enough electrons to fuel a net zero future.

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