On December 16, 2021, the Commission issued its final rule on transmission line ratings that reforms both the pro forma Open Access Transmission Tariff (“OATT”) and the Commission’s corresponding regulations in an effort to improve the accuracy and transparency of transmission line ratings. The Commission stated that this rule will more efficiently utilize the transmission grid and help lower costs for consumers.
In August 2019, the Commission staff issued a whitepaper entitled “Managing Transmission Line Ratings,” which included background on common transmission line rating approaches, current practices in Regional Transmission Operators (“RTOs”) and Independent System Operators (“ISOs”), a review of pilot projects, and a discussion of potential improvements. On September 10 and 11, 2019, the Commission held a technical conference to discuss what transmission line ratings and related practices might constitute best practices and what, if any, Commission action would be needed in these areas. The Commission followed up the technical conference with a Notice of Proposed Rulemaking on November 19, 2020.
The Commission’s final rule requires all transmission providers, both inside and outside of organized markets, to use ambient-adjusted ratings as the basis for evaluating near-term transmission services to increase the accuracy of near-term line ratings. Previously, line ratings were based on conservative assumptions about worst-case scenarios. The final rule does not mandate the adoption of dynamic line ratings but establishes four ways to address the inaccurate representation of system transfer capability. First, the final rule requires the implementation of ambient-adjusted ratings and seasonal ratings. Second, the final rule requires all RTOs/ISOs to establish and implement systems and procedures necessary to allow transmission owners to electronically update transmission line ratings at least hourly. Third, the final rule requires transmission providers to use uniquely determined emergency ratings for contingency analysis in the operations horizon and in post-contingency simulations of constraints. Finally, the final rule requires transmission owners to share transmission line ratings and transmission line rating methodologies with their respective transmission providers and, in RTOs/ISOs, with their respective market monitors, and to maintain a database of line ratings and rating methodologies on the provider’s Open Access Same-Time Information System site, or on another password-protected information site.
As Chairman Glick emphasized in the December Commission meeting in which the final rule was issued, “[i]f we are going to meet the needs of the grid of the future while keeping customer rates just and reasonable and maintaining grid reliability, we need to squeeze everything out of our existing grid. Today’s final rule is a huge step forward in making more efficient use of our transmission system and saving money for customers.”
The final rule also notes that FERC has opened a proceeding in AD22-5-000 to explore the potential for further action on dynamic line ratings.
Transmission providers must submit compliance filings within 120 days of the effective date of the rule.