Stability Study Issues

1. Stability Study Issues CMWG August 27, 2008 Beth Garza

2. Outstanding issues • What efforts has ERCOT taken to validate PSS assumptions? • Should ERCOT publish which units have a PSS? • Should ERCOT develop stability limits under additional scenarios? • What can be done to increase the stability limit? • Who is responsible for PSS tuning? CMWG / BGarza

3. What efforts has ERCOT taken to validate PSS assumptions? • All QSEs with Resources were recently surveyed about the status of their Power System Stabilizer • The request for information was initially distributed via Notice W-A101907-02 on November 2, 2007. • Information for all but a handful of generators was available to ERCOT by the end of March 2008. • Information provided to ERCOT via this survey includes: • Confirmation of the existence and/operability of a PSS • Determination of whether tuning was performed • Where they exist, copies of tuning studies • This information has already been included in ERCOT’s Planning and Operations models. CMWG / BGarza

4. Should ERCOT publish which units have a PSS? • There are multiple and conflicting Protocol references that may be used to provide direction on this issue. • ERCOT proposes to issue a Market Notice stating our intention to publish the list of Generators and indicating whether they do or do not have a PSS. • Resource Entities concerned that this would violate the protected status of this information would be asked to justify their position. CMWG / BGarza

5. DRAFT Proposed Notice LONG DESCRIPTION: Several Market Participants in the Congestion Management Working Group (CMWG) have requested that ERCOT post on the Market Information System (MIS) Public Area which Generation Resources have and do not have a Power System Stabilizer (PSS). ERCOT does not consider the presence of a PSS to be Protected Information under Section 1.3.1.1, Items Considered Protected Information, of the ERCOT Protocols. However, before posting such information, ERCOT would like to determine whether any Resource Entity considers the presence of a PSS to be Protected Information under Section 1.3.1.1 of the ERCOT Protocols. Resource Entities shall describe why the presence of a PSS would be considered Protected Information (i.e., Resource specific design data). All responses will be considered by ERCOT in making a final determination on whether to post the information on the MIS Public Area. ACTION REQUIRED: Resource Entities only need to respond to this Notice if they believe that the presence of a PSS on a Generation Resource should be considered Protected Information under Section 1.3.1.1 of the ERCOT Protocols. Resource Entities shall email a detailed response to their ERCOT Account Manager or to ClientRelations@ercot.com by 5:00 P.M. on __________, 2008. ADDITIONAL INFORMATION: A follow-up Notice will be issued to Market Participants indicating a final determination on the issue. CMWG / BGarza

6. Should ERCOT develop stability limits under additional scenarios? • The Dynamics WG is scheduled to provide an annual update to their base case during Q4 2008. • Prior to performing an updated study with the new dynamics base case, ERCOT proposes to distribute proposed Study Scope to Stakeholders for comment. • CMWG, DWG, others? CMWG / BGarza

7. What can be done to increase the stability limit? Current and expected practice: • All generators operate with a well-tuned PSS • Evaluations performed as part of the CREZ studies have only validated that ‘expected’ transfers in 2012 are transient stable. • No stability transfer studies have been performed for years beyond 2012. New efforts: • Add PSS at suitable locations to damp inter-area oscillations. • Add new transmission to decrease the ‘electrical distance’ between units in ERCOT. Oncor has already performed a quick stability study dated 08132008 that provides estimated impacts related to new transmission. CMWG / BGarza

8. Who is responsible for PSS tuning? • Resource Entities are responsible for tuning the PSSs • Nodal Operating Guides more clearly address responsibilities related to PSSs than current Operating Guides. CMWG / BGarza

9. Operating Guides 2.2.4 Automatic Voltage Regulators and Power System Stabilizers Reference: Protocol Section 6.5.7.2, QSE Responsibilities (In Part) …(4)Each QSE’s Generation Resource providing VSS shall operate with the unit’s Automatic Voltage Regulator (AVR) set to regulate generator terminal voltage in the voltage control mode unless specifically directed to operate in manual mode by ERCOT, or when the unit is going On- or Off- line. If the QSE changes the mode, other than under ERCOT direction, then the QSE shall promptly inform ERCOT. Any QSE-controlled power system stabilizers will be kept in service unless specifically permitted to operate otherwise by ERCOT. QSEs’ control centers will monitor the status of their regulators and stabilizers, and shall report abnormal status changes to ERCOT… CMWG / BGarza

10. Operating Guides / 2.2.4 Generator Automatic Voltage Regulators (AVR) and power system stabilizers (PSS) will be kept in service whenever possible. Generation Resources (GR) shall notify their Qualified Scheduling Entity (QSE) who in turn will promptly notify the ERCOT Control Area Authority when a voltage regulator or stabilizer is taken out of service due to equipment maintenance or failure and when it is returned to normal operation. ERCOT is responsible for notifying the appropriate TO of such AVR and PSS status changes. QSEs shall supply AVR and PSS status logs to ERCOT upon request. Performance tests shall be conducted on Automatic Voltage Regulators every five years or if equipment characteristics are knowingly modified. The test reports should include the minimum and maximum excitation limiters, volts/hertz settings, gain and time constants, type of voltage regulator control function, date tested, and voltage regulator control setting. Excitation systems, including power system stabilizers, shall also be tested every five (5) years. CMWG / BGarza

11. 2.2.6 Power System Stabilizers / Nodal Operating Guides • Generation Resources with a Power System Stabilizer (PSS) for which settings have been determined by the Generation Resource or by ERCOT shall keep the PSS in service when the Generation Resource is in normal operating range. Generation Entities shall notify their QSEs, who in turn will notify ERCOT of the circumstances when a stabilizer is unavailable due to maintenance or failure and when the stabilizer returns to normal operation. ERCOT is responsible for notifying the appropriate TO of such PSS status changes. QSEs shall supply PSS status logs to ERCOT upon request per Protocol Section 6.5.5.1, Changes in Resource Status. • Synchronous Generation Resources greater than 10 MW installed after January 1, 2008 shall install a PSS and place the PSS in service within 180 days after unit commissioning. The Generation Resource shall determine PSS settings to dampen modes with oscillations within the range of 0.2 Hz to 2 Hz. The PSS settings shall be tested and tuned for adequate damping during PSS commissioning. Final PSS settings shall be provided to ERCOT and the TSP within 30 days of commissioning. CMWG / BGarza

12. 2.2.6 Power System Stabilizers / Nodal Operating Guides (3) For synchronous Generation Resources greater than 10 MW installed on or before January 1, 2008. (a) If a PSS has been installed for the Generation Resource, the Generation Resource may voluntarily determine settings to dampen modes with oscillations within the range of 0.2 Hz to 2 Hz, subject to the following limitation. The PSS on any Generation Resource for which PSS settings had been determined and the PSS had been commissioned prior to January 1, 2008 must remain in-service with the previously determined settings, unless the Generation Resource is directed by ERCOT to modify the settings. The PSS settings shall be tested and tuned for adequate damping prior to placing the PSS on line. The Generation Resource shall notify ERCOT (1) whether or not a PSS has been installed; and (2) whether or not PSS settings have been determined and the PSS has been or will be placed in-service. If the PSS has been or will be placed in-service, the Generation Resource will provide the stabilizer settings to ERCOT and the TSP within 30 days of commissioning. (b) If a PSS has been installed but has not been placed in service, ERCOT may determine and provide the Generation Resource with recommended PSS settings. Within 180 days of ERCOT providing recommended PSS settings to the Generation Resource or at a time mutually agreeable to ERCOT and the Generation Resource, the Generation Resource shall test and tune the PSS to dampen modes with oscillations within the range of 0.2 to 2 Hz or as specified by ERCOT, and place the PSS in-service. Final PSS settings shall be provided to ERCOT and the TSP within 30 days of commissioning. CMWG / BGarza

13. 2.2.6 Power System Stabilizers / Nodal Operating Guides • If an excitation system on a synchronous Generation Resource greater than or equal to 10 MW is upgraded or replaced after January 1, 2008, the Generation Resource shall install a PSS, determine PSS settings to dampen modes with oscillations within the range of 0.2 to 2.0 Hz, and place the PSS in-service. The settings shall be tested and tuned for adequate damping during excitation system commissioning. Final PSS settings shall be provided to ERCOT and the TSP within 30 days of commissioning. • If ERCOT determines a change in PSS settings for a synchronous Generation Resource would improve overall system performance, ERCOT shall coordinate with the Generation Resource owner to determine appropriate settings. Within 180 days of determining appropriate settings, the Generation Resource owner shall test and tune the PSS to dampen modes with oscillations as requested by ERCOT and place the PSS in-service. Final PSS settings shall be provided to ERCOT and the TSP within 30 days of commissioning. • Generation Entities shall conduct performance tests on Power System Stabilizers which have settings or verify PSS performance through comparison with operational data at least every five years, or if equipment characteristics are knowingly modified, within 30 days of the modification. • The results of the most recent PSS test shall be supplied to ERCOT and the Transmission Service Provider within 30 days of a request from ERCOT. CMWG / BGarza

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