Advanced Facility Ratings Management – FERC Order 881

Often, static ratings reflect a manufacturer’s “nameplate ratings,” reflecting worst-case assumptions. While the assumptions used to determine the static ratings of transmission lines vary by operator, they are typically assumptions such as an ambient temperature of 40 degrees Celsius (104 degrees Fahrenheit), wind speeds and directions of .61 meters (2 feet) per second with a 90-degree wind to conductor angle, and clear skies with sunlight at midday. In the IPS® system, these assumptions can be adjusted according to the customer’s requirements. For all rated values, the system includes limits imposed by the protection system for overcurrent and distance protection. These limit values are calculated in the system by the IPS®SLC (Safe Load Calculation) module.

Traditionally, seasonal assessments are calculated similarly to static ratings but with different assumptions about environmental conditions for summer and winter. In support of FERC 881, users will define all four seasons, although not necessarily three months each. Assigning ambient temperature assumptions (typically based on 5- or 10-year historical maximums) for each season, this is generally used for planning purposes. In the future, seasonal assessments will also consider solar irradiance (day and night). Emergency Ratings may also be established for seasonal evaluations.

For FERC 881, you must provide AARs on an hourly basis with a 10-day forecast for all applicable equipment documented in the Facility Rating Methodology used. IPS is integrating weather data to provide real-time weather data by location and all historical data needed to meet the FERC 881 requirement of 5 years. AARs will account for static design assumptions that are modified hourly by ambient temperature and solar irradiance. FERC 881 requires that AARs be recalculated whenever the temperature changes to 5 degrees or more since the last calculation. IPS allows any desired temperature range down to 1 degree.