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Appropriate Ratings April 11, 2013

OPSTF – Issue. Appropriate Ratings April 11, 2013. List of Issues:. 3(e) Ensure 5-yr Plan project completion is timely 4(a) Ensure Load Forecast and Ratings consistency 4(c) Make planning more conservative by using normal ratings for select contingencies

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Appropriate Ratings April 11, 2013

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  1. OPSTF – Issue Appropriate Ratings April 11, 2013

  2. List of Issues: 3(e) Ensure 5-yr Plan project completion is timely 4(a) Ensure Load Forecast and Ratings consistency 4(c) Make planning more conservative by using normal ratings for select contingencies 8(c) Generator unit unavailability

  3. Contributing Factors 1. Construction delays could lead to overloads in real time. 2. Planners may miss overloads that occur in operations when multiple generating units are out. 3. Operators use dynamic ratings to lower facility ratings during extremely hot weather. 4. Load forecasts used in planning may be less than load levels seen during real time operations. 5. Planning analysis assumes all facilities are in-service. 6. Actual resource dispatch is different from that modeled in planning cases. 7. Outages (forced & planned) are generally unknown when planning studies are performed.

  4. ERCOT Study • A Sept. 2012 screening study on the 2015 SP case ran credible single contingencies (G-1+N-1 & A-1+N-1 excluded). • Facility loading levels above 90% & 95% identified • Results reviewed by OPSTF w/ six TSPs providing written responses: AEN, BEPC, CNP, LCRA, ONCOR, STEC • OPSTF concluded 90% too conservative (and 97% ineffective) • The six TSP responses indicate the effect for using 95% will be to accelerate improvements by 1 to 2 years

  5. Expected Benefits • Better aligns Planning w/ RT Operational conditions • Reduces impact of long term equipment outages • Earlier construction start should ease outage scheduling • Reduces the need for planned load shedding • Having more capacity sooner will increase grid Reliability • Will likely reduce congestion while improving the use of available generation capacity

  6. Recommendation OPSTF Recommendation: • Require transmission facility loading level thresholds be set at 95 percent of facility rating • Refer the proposal to the PLWG to develop a Revision Request to change the ERCOT Planning Criteria with a time-sufficient implementation schedule • PLWG to also address whether any exceptions are appropriate

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