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Use of Manual SCED Executions and Offsets and the Calculation of GTBD

Use of Manual SCED Executions and Offsets and the Calculation of GTBD. David Maggio ERCOT, Real-Time Market Integration. Use of Manual Executions and Offsets.

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Use of Manual SCED Executions and Offsets and the Calculation of GTBD

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  1. Use of Manual SCED Executions and Offsets and the Calculation of GTBD David Maggio ERCOT, Real-Time Market Integration

  2. Use of Manual Executions and Offsets • During the first two months following the transition to the Nodal Market, there have been periods in which ERCOT Operators have had to utilize manual SCED executions and offsets • Off-cycle SCED executions are typically used to help the following: • Exhaustion of Regulation • Frequency issues (i.e. Resource Start-up and Shut-down or a unit trip) • Congestion issues (i.e. following the activation of a new constraint) • Manual SCED offsets are typically used to help the following • Exhaustion of Regulation • Accounting for Large Schedule Changes (i.e. DC Tie Schedules)

  3. Trend of Manual Execution and Offsets Since Go-Live

  4. Use of Manual Executions and Offsets • The amount of manual SCED executions and offsets has decreased significantly since the middle of December • Improvements to the Generation-to-be-Dispatched (GTBD) calculation may decrease the need for Operators to use offsets • Using the short-term load forecast (STLF) as opposed to the medium-term load forecast (MTLF) • Considering of DC Tie schedule changes • ERCOT Operators will still likely need to take these manual actions as a result of the scenarios previously mentioned

  5. Calculation of GTBD • The Generation-to-be-Dispatched (GTBD) value is used by SCED as the Generation Requirement • The sum of Resource base-points should equal to GTBD honoring all constraint functions (Energy Offer Curves, system congestion, etc…) • GTBD is calculated as: (Sum of Generation) + K1*(10*65.3*(Scheduled Freq. – Actual Freq.) – K2*(net non-conforming load – net filtered non-conforming load) + K3*(5*Predicted Load Ramp Rate)

  6. Market Trials Tuning of GTBD • The K factors were tuned with AREVA Staff as part of market trials during the Full-System Market and Reliability testing • The factors were chosen based on what numbers appeared to give ERCOT the best frequency control • The resulting K factors used at Go-Live were: • K1 = 2 • K2 = 0 • K3 = 1.2 • The was concern about using a single 4 second snapshot of non-conforming for GTBD, so K2 was left at 0

  7. Continued Tuning of GTBD • Following the transition to the Nodal Market, some changes were to both the K factors and the calculation of GTBD • On December 10th, K1 was changed from 2 to 0 • Like K2, there was concern with using a 4 second snapshot of frequency deviation to determine a 5 minute SCED base-point • On January 26th, the GTBD calculation was changed to calculate the predicted load ramp rate using the STLF (5-minute granularity) as opposed to the MTLF (1-hour granularity) • The MTLF is not able to capture intra-hour load changes. • On January 26th, K3 was changed from 1.2 to 1.1 • This change was made as a result of the GTBD calculation change of the 26th

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