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System Strength/Short Circuit Current Minimum Requirement

System Strength/Short Circuit Current Minimum Requirement. June 5, 2014. Background. In parallel with the ERCOT PREZ Study, Sharyland has been evaluating the transmission system performance in the Panhandle region, specifically:

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System Strength/Short Circuit Current Minimum Requirement

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  1. System Strength/Short Circuit Current Minimum Requirement June 5, 2014

  2. Background In parallel with the ERCOT PREZ Study, Sharyland has been evaluating the transmission system performance in the Panhandle region, specifically: • Including generation resources meeting Section 6.9 of the ERCOT Planning Guides • Completed assessments for the Panhandle Region including: • steady state voltage security • transient voltage stability • system strength assessments • Issue: • The ERCOT Panhandle region does not have synchronous generators/machines or loads, which provide system strength to the grid via short circuit current ratio (SCR) • For wind generation control systems to work properly, a strong SCR is necessary • Synchronous condensers can provide improved system strength to mitigate the issues – but what should be the criteria for SCR for a bus and a region? • Criteria should apply to both Planning and Operations limits

  3. Weighted Short Circuit Ratio (WSCR) • ERCOT staff has proposed a minimum Weighted Short Circuit Ratio (WSCR) of 1.5 for the Panhandle region • WSCR would become a default minimum criteria – but not proposed as a Protocol or Planning Guide requirement • There are no known WSCR minimums elsewhere - Also important to differentiate between WSCR and the SCR requirements at the POI for turbine vendors • Sharyland utilized a Composite Short Circuit Ratio (CSCR) approach to evaluate “optimal” amount of synchronous condensers required for in the Panhandle • Both CSCR and WSCR approaches observed to yield similar results • Sharyland deems it important to investigate the “technical basis/justification” for the WSCR threshold – synchronous condenser requirements are very sensitive to the target • Using results from system strength studies performed by Sharyland, a target of 1.2 for CSCR/WSCR seems appropriate maintain control stability and 3 GW of wind exports do not require Synchronous Condensers • Using a 1.5 CSCR/WSCR requires 250 MW of Synchronous Condensers at 3 GW of wind exports

  4. Proposal for ROS Consideration • ROS to assign a working group to address the following: • Review the WSCR methodology developed by ERCOT • Determine the appropriate target/criteria for minimum POI SCR and Regional WSCR

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