Board approves additional Southern Cross determinations

At the April Ercot Board meeting, Janice Ayson, ERCOT’s Lead Strategic Advisor, provided an overview of the Southern Cross project and ERCOT’s process for completing certain tasks set forth in directives from the PUCT.

The Southern Cross project was proposed by Pattern Energy and received approval from FERC in May 2014 for interconnection to ERCOT. Subsequently, the PUCT issued an order in Project No. 45624, the City of Garland’s application for a CCN to build a new 38-mile-long 345-kV transmission line connecting the proposed 2, 000 MW of the Southern Cross DC tie to ERCOT, imposing certain conditions on the proposed interconnection.

In May 2017, the PUCT directed ERCOT to complete a number of tasks set forth in 14 directives, including requiring ERCOT to study various issues related to the new DC tie and make determinations as to whether any actions needed to be taken by ERCOT in order to accommodate the new DC tie. ERCOT staff has been working with stakeholders and Southern Cross to complete the tasks set forth in the directives.

PUCT Directive 6: ERCOT Determination regarding Any Needed Transmission Upgrades

John Bernecker, ERCOT’s Manager of Transmission Planning Assessment, discussed the PUCT’s directives and associated determinations. PUCT Directive 6 required ERCOT to study and determine what transmission upgrades, if any, are necessary to manage congestion resulting from power flows over the Southern Cross DC tie. ERCOT was also required to make any necessary revisions to its standards, guides, systems and protocols and certify to the PUCT when it completed these actions.

In 2019, ERCOT conducted transmission analyses, which initially determined that upgrades would be needed to accommodate the model flows over the Southern Cross DC tie under certain system conditions. However, no transmission upgrades were ultimately necessary to manage congestion because Planning Guide Revision Request (PGRR) 077, approved in October 2020, requires ERCOT to curtail assumed DC tie flows when necessary to meet reliability criteria. Future transmission planning studies would not identify any reliability-based need for transmission upgrades following the interconnection of the tie. In addition, ERCOT’s resolution to Directive 7 showed that existing operational and market mechanisms could be used to manage congestion due to flows of the DC tie.

ERCOT staff recommended that the Board accept ERCOT staff’s determination that: 1) no transmission system upgrades are necessary to manage congestion resulting from power flows over the Southern Cross DC tie; and 2) ERCOT expects that it may need to re-dispatch generation and/or limit flows across the Southern Cross DC tie to manage constraints in real time.

Directive 8 – ERCOT Determination regarding Voltage Support

In its Directive 8, the PUCT required ERCOT to: (a) study and determine whether Southern Cross or any other entity scheduling flows across the Southern Cross DC tie should be required to provide procure voltage support service or primary frequency response; (b) implement necessary revisions to its standards, guides, systems and protocols; and (c) certify to the PUCT when it is completed these actions. The instant certification only concerns voltage support, as ERCOT’s determination concerning primary frequency response was approved by the Board on August 7, 2018.

ERCOT noted that NPRR1098 (DC Tie Reactive Power Capability Requirements) and Nodal Operating Guide Revision Request (NOGRR) 234, which were approved by the PUCT on March 31, 2022, revised protocols and operating guides to require that new or replaced DC ties have at least 0.95 power factor leading/lagging reactive power capability.

The transmission analysis conducted for Directive 6 determined that there would be voltage stability constraints associated with exports across the tie but any transmission improvements necessary to resolve those constraints would be lessened by the DC tie having the capability to provide that reactive power capability.

ERCOT staff recommended that the Board accept ERCOT staff’s determination that any DC tie facility energized after January 1, 2021 should be required to have at least 0.95 power factor leading/lagging reactive power capability; and (2) no further action is necessary to resolve Directive 8 regarding voltage support service.

The ERCOT Board unanimously approved the determinations on PUCT Directives 6 and 8 with no discussion.