This article answers key FERC 881 questions: when it was issued, what it changes, and how line ratings impact grid reliability.
When Was FERC Order 881 Issued: History
FERC Order 881 was issued on December 16, 2021, by the Federal Energy Regulatory Commission (FERC). According to the commission, the purpose of this rule is to utilize the transmission grid in the United States efficiently. This step improves the accuracy and transparency of the Bulk Electric System (BES) Across North America.
The question is how will this order provide the changes that FERC predicts. To understand this, you must know how line ratings evolve in the bulk electrical system. Traditionally, conservative static assumptions were used. Static line ratings, known as “nameplate ratings,” are often based on worst-case scenarios, the highest temperatures, and low wind speeds. This safety-first theory prevents overheating, which can cause brownouts or blackouts, and excessive sagging of the electrical lines, which could lead to public hazards.
The Problems with Static Line Ratings
The problems with the worst-case scenario described in the previous paragraph are threefold and do not account for the weather’s dynamic nature. Temperatures fluctuate, and resistance lowers in colder temperatures. This lower resistance means higher electrical conductivity, allowing electricity to flow more easily. Electric lines expand and sag during warmer temperatures; you can often see the sag most dramatically in areas with cold nighttime and hot daytime temperatures, such as Texas, California, New Mexico, and Arizona. However, even if the sagging isn’t as noticeable, sag increases resistance by increasing the distance that electricity travels. More resistance = slower energy flow.
Another problem with Static Line Ratings is that they do not address wind. Everyone in Oklahoma knows that “when the wind goes sweeping down the plains” isn’t just a catchy lyric. Folks in Chicago are so familiar with the wind that their city is known worldwide as “The Windy City.” But sometimes the wind is friendly to electrical lines, cooling the temperature. Conversely, in desert areas of the USA, the lack of wind can cause the heat to become even more oppressive, increasing resistance and slowing the flow of electricity.
The third issue with Static Line Ratings is that they fail to address solar irradiance, which is the amount of solar power received in a specific area at a given time. This intensity of the sunline is affected by the sun’s angle, the distance the sun is from the Earth, and atmospheric conditions such as clouds and haze that can scatter solar radiation, reducing the irradiance. In the summer, longer days and the earth’s tilt toward the sun affect solar irradiance. Winter days, shorter and further away from the sun, experience less solar energy.
Next Steps: Seasonal Line Ratings
Slightly more dynamic and able to handle seasonal fluctuations in temperature are Seasonal Line ratings. Condition assumptions for summer and winter being vastly different in temperature is an extremely common-sense way to upgrade from the more conservative Static Line ratings worst-case scenario methodology. However, the Seasonal Line ratings only consider temperatures and use conservative temperature assumptions, often 95 degrees in the summer and 32 degrees in the winter. Additionally, transmission owners historically have relied on 5 to 10-year historical highs and lows for their calculation; this can be a concern for the overall warming trends seen in recent years.
What are Ambient Adjusted Ratings?
Ambient Adjusted ratings are calculations based on temperature and solar heating (night vs. day). Using ambient air temperature forecasting, ambient adjusted ratings can help balance supply with demand, often a significant pain point in extreme temperatures. FERC and other regulatory agencies worldwide, along with electrical engineers from companies, have developed the concept of Ambient-Adjusted Ratings. Two pain points of Static Line Ratings that Ambient adjusted ratings consider are temperature and solar heating. Knowing that there is less solar irradiance allows for more electrical flow through lines. Ambient Adjusted ratings consider that the lower the temperature, the more flow is possible. Ambient Adjusted Ratings allow flexibility that the worst-case scenario restrictions of Static Line Ratings do not. This improved consideration means more energy flowing through the lines and better grid reliability. This reliability can lead to cost savings as poor gid conditions lead to higher maintenance and decreased customer satisfaction.
The future of Ratings: How do Dynamic line ratings work?
While not a current requirement for transmission owners, dynamic line ratings (DLRs) are the future. DLRs allow for the most significant degree of system control. DLRs work by using real-time ambient conditions such as air temperature, wind conditions (direction and speed), and solar irradiance intensity (not just day or night, but cloudy or clear, etc.), among other things. Sensors on transmission lines collect and send data on temperature, wind speed, and direction and can sense solar radiations, giving large amounts of data more frequently (e.g., hourly or every 15 minutes). This data can be analyzed using advanced algorithms to determine the line’s capacity. These analytics determine the maximum safe current, and the transmission operators can adjust the flow. Dynamic line ratings essentially negate the weaknesses of Static line rantings discussed. DLR calculations, however, can be costly, including the cost of equipment and data management, especially data storage.
Advanced Facility Ratings Technology
FERC 881’s sweeping changes to Facility Rating Management are mandated by July 2025. In the new operating rules, seasonal rations must be defined for all four seasons. These seasons will vary by climate, so three equal months for each seasonal rating would not be required. Instead of basing ratings on historical highs and lows, Ambient Adjusted Ratings (AARs) must consider the static rating assumptions, modified hourly by ambient temperature and solar irradiance. FERC 881 requires AARs to be adjusted anytime the temperature changes by 5 degrees or more since the last adjustment.
With IPS®, the assumptions for the static ratings can be adjusted in any way the client wishes. Our System includes limits imposed by the protection system for all overcurrent and distance protection through our IPS® Safe Load Calculation Module. Advanced Facility Ratings Management (AFRM) collects rating information from Enterprise Asset Management, Network Model Management (NMM), and any allowable external system currently used. The software calculates and aggregates facility ratings using the network connectivity model Common Information Model (CIM). AFRM calculates ambient adjusted and seasonal ratings based on the weather service provider’s data, then manages and stores all the relevant rating data based on internal and regulatory requirements. It can integrate the data into operational information systems, such as SCADA/EMS, and business systems, including regulatory reporting. AFRM becomes a central hub for rating information inside the utility.
The software can interface with your external data sources and turn all your raw data into actionable information. This allows you to work smarter, budget wisely, and deliver on the demands of the governing regulatory bodies and the power grid today and in the future. Book a Demo with us today!
