Title: Combined Cycle Power Blocks with Multiple Voltage Interconnections
Next Group:
Next Step:
Status: Approved on 11/17/2008
Effective Dates:

or per the Nodal Protocol Transition Plan http://www.ercot.com/mktrules/protocols (12/01/08 Nodal Protocols Library)


Date Gov Body Action Taken Next Steps
07/17/2008 PRS Deferred/Tabled PRS Impact Analysis Review
09/24/2008 PRS Recommended for Approval Impact Analysis Review
11/17/2008 BOARD Approved
11/06/2008 TAC Recommended for Approval Board Consideration
10/23/2008 PRS Recommended for Approval TAC consideration
06/19/2008 PRS Recommended for Approval Impact Analysis Review
05/22/2008 PRS Referred Review by TPTF

Voting Record

Date Gov Body Motion Result
07/17/2008 PRS To table NPRR128 pending development of an Impact Analysis. Passed
09/24/2008 PRS To recommend approval of the PRS Recommendation Report as amended by ERCOT’s comments. All Market Segments were present for the vote Passed
11/17/2008 BOARD Approved NPRR128 as recommended by TAC. Passed
11/06/2008 TAC To recommend approval as recommended as approved PRS. Passed
10/23/2008 PRS To endorse and forward the PRS Recommendation Report and Impact Analysis to TAC. Passed
06/19/2008 PRS To recommend approval of NPRR128 as submitted. Passed
05/22/2008 PRS To refer NPRR128 to the TPTF for consideration. Passed

Vote tallies here reflect individual votes, not the weight of the votes by market segment. Affirmative votes are not recorded in these vote tallies. For additional details on the voting record, please consult the Recommendation or Action Report, or the official vote tally if available, as posted in the key documents.


Status: Approved
Date Posted: Apr 25, 2008
Sponsor: Calpine
Urgent: No
Description: 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.
Reason: Current 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.

Key Documents

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