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Base Point Deviation During SCED Shortened Intervals- Presentation to SEWG

Base Point Deviation During SCED Shortened Intervals- Presentation to SEWG. Jim Galvin- Chair, Settlements and Extract Working Group 9/20/2010. Background. Market trials settlement review of Base Point Deviation has identified an anomaly in the Base Point Deviation (BPD) settlement algorithm

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Base Point Deviation During SCED Shortened Intervals- Presentation to SEWG

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  1. Base Point Deviation During SCED Shortened Intervals- Presentation to SEWG Jim Galvin- Chair, Settlements and Extract Working Group 9/20/2010

  2. Background • Market trials settlement review of Base Point Deviation has identified an anomaly in the Base Point Deviation (BPD) settlement algorithm • Current algorithm calculates BPD correctly when SCED intervals are 300 seconds (5 min) in duration • For SCED intervals less than 5 min, it is possible for a BPD to be calculated when a resource follows all instructed Base Points and ramping conditions • Goal in this presentation is to raise issue and discuss possible long term correction and interim consideration

  3. BPD- Algorithms Under-generation Over-generation

  4. Focus on AABP • Identified issue focuses on the calculation of the Adjusted Aggregate Base Point (AABP) • Base points are issued based on resource ramping capabilities • Calculation for AABP is: • Base Point for the interval (y) • Base Point for previous interval (y-1) • {y + (y-1)/2} * TLMP/900 • TLMP is total seconds for the SCED period which is divided by the total of 900 seconds in a 15-minute settlement interval

  5. Example Resource has a 10 MW per minute ramp rate and is sitting at 100 MW prior to dispatch for the next interval SCED dispatches the unit (red line) with desired BP of 150 MW SCED interval is shortened to 150 seconds (2.5 minutes) and unit follows ramp and reaches 125 MW (orange line) Next SCED interval considers ramp rate and telemetered generation and sets next base point to 175 MW (green line) Over the course of the 15-min interval, 5 total SCEDs are run and the resource follows its ramp in trying to reach the desired BP

  6. Example Settlements calculates an Aggregate Adjusted Base Point using the algorithm on previous page or 190.4 MW Time Weighted Telemetered Generation (TWTG) is calculated at 43.75 MWh for the 15-min interval, or 175 MW (Under-generation) Tolerance band is the % tolerance (5%) or 180.9 MW (45.22 MWh) ERCOT will calculate a BPD Charge of 45.22 MWh – 43.75 MWh multiplied at the RTSPP of $100, or $147.4

  7. Example- Over-generation Example shows resource ramping down with same 10 MW per minute ramp rate Unit follows its ramp and desired BP each SCED period Resource is charged a BPD charge over the tolerance of 172.9 MW (43.22 MWh) and the TWTG of 43.75 MWh at the RTSPP of $100, for a charge of $52.50

  8. Questions

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