On May 19, 2022, FERC issued Order No. 881-A responding to arguments raised on rehearing of Order No. 881, which revised the pro forma OATT and FERC regulations to increase the accuracy and transparency of electric transmission line ratings. FERC ultimately sustained the result of Order No. 881, denying all requests for rehearing, but did provide a number of clarifications regarding the new requirements.

Order No. 881 adopted a number of provisions aiming to more efficiently utilize the existing transmission grid by improving transmission line ratings, which as FERC explained, were typically based on conservative assumptions about worst-case, long-term air temperature and other weather conditions that could lead to the underutilization of the transmission grid (see December 22, 2022 edition of the WER). Among other things, Order No. 881 requires public utility transmission providers to: 1) implement ambient-adjusted ratings (“AAR”) on the transmission lines over which they provide transmission service; 2) use uniquely determined emergency ratings; 3) maintain a database of transmission owners’ transmission line ratings and transmission line rating methodologies on the transmission provider’s OASIS site or other password-protected website; and 4) to share transmission line rating and transmission line rating methodologies with their respective transmission provider(s) and with market monitors in RTOs and ISOs. Several entities filed requests for rehearing and clarification regarding the new AAR requirements, including, among other things, the annual recalculation of seasonal line ratings and the new transparency requirements adopted in Order No. 881.

FERC denied all requests for rehearing, explaining that inaccurate transmission line ratings result in FERC-jurisdictional rates that are unjust and unreasonable, but did clarify that, among other things:

  • No revisions are required to the assumptions used in the existing transmission planning and development context, Critical Energy Infrastructure Information (“CEII”) requirements, or the role and authority of market monitors;
  • There is no prescribed procedure for recalculating seasonal line ratings, including determining which inputs have changed in a year, or require transmission owners to undertake unnecessary changes from year to year;
  • Transmission providers must implement AARs on all transmission lines, but have the discretion to post transmission line ratings and methodologies-related data to a password protected section of their OASIS site or another password protected website;
  • If a transmission provider establishes higher transmission line ratings, it will have to evaluate or reevaluate its applicable protection systems for that facility; and
  • Relay settings should only exceed AAR values in a minority of situations (as opposed to the majority of situations as FERC inadvertently stated).

FERC also denied a request for clarification regarding a specific line rating methodology, confirming that the appropriate proceeding for such a determination is the transmission provider’s Order No. 881 compliance filing.

A copy of Order No. 881-A is available here.