On March 19, 2009, FERC issued a Notice of Proposed Rulemaking (“NOPR”) to approve six Modeling, Data and Analysis (“MOD”) Reliability Standards that would require certain users, owners and operators of the transmission system to develop consistent methodologies for the calculation of ATC. NERC originally submitted such standards to the Commission on August 29, 2008 and November 21, 2008. In the NOPR, the Commission described each Reliability Standard being proposed:

MOD-001-1 – Available Transmission System Capability Reliability Standard

In Order No. 890, the Commission did not require a uniform methodology for calculating ATC. However, as set forth by the Commission in the NOPR, differences in implementation of ATC methodologies and a lack of coordination between transmission service providers have resulted in ATC being overestimated, causing transmission systems to be oversold and interconnection reliability limits to be exceeded.

Proposed MOD-001-1 would require transmission service providers and transmission operators to select and implement one of three methodologies for calculating ATC for each path for each time frame (hourly, daily or monthly) for the facilities in its area.

The three proposed methodologies are as follows:

  • MOD-028-1 – Area Interchange Methodology – This methodology would require a determination of incremental transfer capability via simulation, from which total transfer capability can then be mathematically derived. Total transfer results are generally reported on an area to area basis.
  • MOD-029-1 – Rated System Path Methodology – This methodology would include an initial total transfer capability, determined via simulation. As with the area interchange methodology, capacity benefit margin, transmission reliability margin, and existing transmission commitments are subtracted from the total transfer capability, and postbacks and counterflows are added, to derive ATC.
  • MOD-030-1 – Flowgate Methodology – This third methodology for calculating ATC begins with an identification of key facilities as flowgates. Total flowgate capabilities are determined based on facility ratings and voltage and stability limits. The impacts of existing transmission commitments are then determined by simulation. To determine the available flowgate commitments, the transmission service provider or operator must subtract the impacts of existing transmission commitments, capacity benefit margin, and transmission reliability margin, and add the impacts of postbacks and counterflows. Available flowgate capability can then be used to determine ATC.

MOD-008-1 – Transmission Reliability Margin Methodology

The Transmission Reliability Margin Methodology standard requires entities to prepare and keep current implementation documents that provide for the calculation of Transmission Reliability Margin, which is the transmission transfer capability set aside to mitigate risks to operations, such as deviations in dispatch, load forecast, outages, and similar other conditions. Proposed MOD-008-1 does not specify a particular approach for calculating this margin.

MOD-004-1 – Capacity Benefit Margin Methodology

The Capacity Benefit Margin Methodology standard requires entities to prepare and keep current implementation documents that provide for the calculation of Capacity Benefit Margin, which is transmission transfer capability set aside to allow for the import of generation upon the occurrence of a generation capacity deficiency.

The Commission also proposed to direct NERC to perform an audit of the various implementation documents developed by transmission service providers to confirm that the complete ATC methodologies are sufficiently transparent to enable the Commission to verify each transmission provider’s calculations. The audit must be completed within 180 days after the effective date of the Reliability Standards, as approved by the Commission in a final rule.

Comments are due 60 days after publication of the NOPR in the Federal Register. The NOPR is available at: http://www.ferc.gov/whats-new/comm-meet/2009/031909/E-5.pdf.