Transcript Stability Study Issues

Stability Study Issues
CMWG
August 27, 2008
Beth Garza
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?
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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.
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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.
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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 [email protected] 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.
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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?
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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.
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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.
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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 Offline. 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…
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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.
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2.2.6 Power System Stabilizers / Nodal Operating Guides
(1) 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.
(2) 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.
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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.
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2.2.6 Power System Stabilizers / Nodal Operating Guides
(4) 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.
(5) 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 inservice. Final PSS settings shall be provided to ERCOT and the TSP within
30 days of commissioning.
(6) 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.
(7) 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.
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