On December 15, 2022, FERC issued an order accepting Arizona Public Service Company’s (“APS”) revisions to its Open Access Transmission Tariff (“Tariff”) that would allow APS to begin using the Flowgate Methodology for calculating Available Transfer Capability (“ATC”) instead of its current Rated System Path Methodology. In addition, FERC denied APS’s request to waive the requirement to post its Total Transfer Capability (“TTC”) values on the Open Access Same Time Information System (“OASIS”).

On July 25, 2022, APS filed revisions to its Tariff to facilitate its transition to the Flowgate Methodology for calculating ATC. In its filing, APS explained that the proposed tariff revisions reflect the transparency and consistency concerns of Order No. 890, which requires public utilities to (1) identify which of the NERC-approved methodologies the utility would use for calculating the conversion of Available Flowgate Capability (“AFC”) values into ATC values (e.g., Area Interchange, Rated System Path, or Flowgate Methodology), (2) provide a detailed description of, including a flow diagram, of the specific mathematical algorithm used to calculate ATC and how each ATC component is derived in the operating and planning horizons, and (3) include such calculations in the utility’s tariff and post a link to the calculation on the utility’s website in Attachment C of the Tariff. In addition to APS’ proposed Tariff revisions, on July 26, 2022, APS filed a petition requesting waiver of the requirements to post TTC values on its OASIS as mandated by section 37.6 of FERC’s regulations and Order No. 890. APS explained that posting the TTC component would have no benefit to transmission customers because customers cannot use TTC values to verify the ATC values under the Flowgate Methodology. The reason for this, APS stated, is that while TTC is referenced as a component of ATC under Order No. 890, TTC is not a component of ATC for transmission providers using the Flowgate Methodology. Instead, APS stated that transmission providers that use the Flowgate Methodology use Total Flowgate Capability (“TFC”) rather than TTC, which is then modified to determine AFC, and AFC is then converted to ATC and posted on OASIS. To address concerns of transparency, APS emphasized that it would automate its TFC calculation, so that its ATC value would be updated on an hourly basis. Without a permanent waiver, APS argued that the posting requirement would be overly burdensome since employees would have to update the TTC value manually.

In its order, FERC conditionally approved APS’s proposed Tariff revisions because the revisions incorporated the necessary requirements of Order No. 890 by providing the mathematical algorithm, diagrams, and explanations for how APS calculates its Flowgate Methodology. However, FERC noted that APS failed to include the link to its calculations on its website in its revised Attachment C and directed APS to submit a compliance filing within 30 days of its order. Additionally, FERC denied APS’s petition to waive the requirement to post TTC values on OASIS. FERC explained that it will only grant temporary or partial waivers in limited circumstances where there is evidence of minimal internal service requests inquiring about ATC values, and where the entity still provides adequate information to customers on the availability of service. FERC reasoned that APS failed to provide such evidence and failed to adequately explain how converting TFC to TTC would be overly burdensome on its staff. FERC determined that because APS engages in transactions with interconnected customers that use TTC, APS is required to continue to post TTC to ensure transparency and reduce undue discrimination.

A copy of the order can be found here.