NPRR #128 · Revision Request
NPRR128 Combined Cycle Power Blocks with Multiple Voltage Interconnections
ReasonCurrent nodal Protocol language defines each configuration of a combined cycle power block to be a single Resource so long as all of the power block’s individual generators are connected to the transmission system at the same nominal voltage level. This requirement is not necessary to the functionality of the ERCOT nodal systems and has unintended consequences on the market and on owners of facilities where generators in the same physically coupled power block have generators connected at different voltages. These facilities must have the generators registered on separate RARFs, which ultimately leads to numerous infeasibilities in Real- Time dispatch and results in capacity being stranded out of the market. (Example: a 2x1 power block, with one combustion turbine (CT) and the steam turbine (ST) connected at 138 Kv, and the remaining CT connected at an adjacent 345 Kv bus must be registered in the market with two RARFs. The ST can only be rated at maximum loading with both CTs on-line but the RARF for that 1x1 configuration can only show half of the ST’s capability since the other CT is registered separately.) The feasibility of Real-Time dispatch is impacted negatively in the sense that the units must move in the same directions up and down a common energy offer curve in response to Security-Constrained Economic Dispatch (SCED) assigned base points because they are physically interdependent. (Example: The 1x1 will have its own configuration in the RARF and flagged in the Current Operating Plan (COP) with its own energy offer curve and the 1x0 CT on 345 Kv will also have its own energy offer curve. SCED base points could conceivably be issued that would have each of the configurations moving in opposite directions on their respective energy offer curves, which would be infeasible due to the physical coupling of all the machines.) It’s also worthy of noting that a combined cycle power block with all generators connected at the same bus can very well end up on different buses at different voltages and resulting Locational Marginal Prices (LMPs) if that common bus has a bus tie breaker that has to be opened at any given time.The machines impacted by the current nodal Protocol language were interconnected to the ERCOT System in good faith and in compliance with the then rules of ERCOT’s Standard Generator Interconnect Agreement (SGIA). Stakeholders have gone to great lengths to ensure that the new market design does not disenfranchise or devalue existing assets or agreements so there is significant precedent for correcting this inequity, particularly when it has no value to the functionality of the ERCOT Market Management System (MMS) and other central systems.
Created2008-05-22
Approved2008-11-17
Sections Affected
6.5.5.2
Summary
This Nodal Protocol Revision Request (NPRR) eliminates the unnecessary restriction that requires all generators in a combined cycle power block to be connected to the bulk electric system at the same voltage level. This change must be made for similarly situated combined cycle units to effectively participate in the very important nodal 168-hour test. Re-done resource asset registration forms (RARFs) must also be constructed and validated prior to implementing these changes.
Action Log 7 milestones
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May 22
PRSReferred→ Review by TPTF
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Jun 19
PRSRecommended for Approval→ Impact Analysis Review
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Oct 23
PRSRecommended for Approval→ TAC consideration
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Nov 6
TACRecommended for Approval→ Board Consideration
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Nov 17
BOARDApproved
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Sep 24
PRSRecommended for Approval→ Impact Analysis Review
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Jul 17
PRSDeferred/Tabled→ PRS Impact Analysis Review
Amendments
| Date | Body | Motion | Result |
|---|---|---|---|
| Sep 24 '08 | PRS | To recommend approval of the PRS Recommendation Report as amended by ERCOT’s comments. All Market Segments were present for the vote | Passed |
Documents 14
Meetings That Took It Up 7
| Date | Meeting | Committee | Status |
|---|---|---|---|
| Nov 6 '08 | TAC Meeting | TAC | Concluded |
| Oct 23 '08 | PRS Meeting | PRS | Concluded |
| Sep 24 '08 | PRS Meeting | PRS | Concluded |
| Jul 17 '08 | PRS Meeting | PRS | Concluded |
| Jun 27 '08 | Credit Work Group Meeting | CREDITWG | Concluded |
| Jun 19 '08 | PRS Meeting | PRS | Concluded |
| May 22 '08 | PRS Meeting | PRS | Concluded |