Document name
WECC Pre/Post-Contingency Plan Guideline
Category
( ) Regional Reliability Standard
( ) Regional Criteria
( ) Policy
(X) Guideline
( ) Report or other
( ) Charter
Document date
February 21, 2014
Adopted/approved by
OIWG/Operating Committee
Date adopted/approved
2/21/2014/05/20/2014
Custodian (entity
responsible for
maintenance and
upkeep)
Operational Issues Work Group
Stored/filed
Physical location:
Web URL:
Previous name/number
(if any)
Status
( ) in effect
( ) usable, minor formatting/editing required
( ) modification needed
( ) superseded by _____________________
(X) other _____________________________
( ) obsolete/archived
W E S T E R N E L E C T R I C I T Y C O O R D I N A T I N G C O U N C I L • W W W . W E C C . B I Z
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WECC Pre/Post-Contingency Plan Guideline
Introduction
The Arizona-Southern California Outages on September 8, 2011 report identified
concerns where entities were operating in an insecure N-1 state on September 8, 2011,
and were relying on post-contingency mitigation plans that did not provide sufficient time
to mitigate the contingencies. An N-1 insecure operating state is characterized as a
state where the BES is exposed to instability, uncontrolled separation, or cascading
outages following a single contingency.
Purpose
This Guideline helps identify for entities when they need to take pre-contingency actions
to prevent post-contingency problems and when its acceptable for an entity to rely on
post-contingency actions to mitigate the impacts of a contingency after the a
contingency occurs. Additionally it recommends best practices for use by transmission
entities in the Western Interconnection to ensure that pre- and post-contingency
mitigation plans prevent unacceptable post-contingency system performance and reflect
the time necessary to take mitigating actions, including control actions, to return the
system to a secure N-1 state.
Pre/Post Contingency
Pre-contingency mitigation measures are necessary when operators are faced with
potential post-contingency conditions that result in facilities exceeding their highest
available emergency rating. To ensure that the transmission system is operated so that
instability, uncontrolled separation, or cascading outages will not occur as a result of the
most severe single contingency and credible multiple contingencies, entities should
comply with applicable versions of TOP-004, Transmission Operations, and other
applicable reliability standards.
As per the Peak Reliability SOL Methodology (based on NERC Standard, FAC-011,
R2.1), acceptable pre-contingency system performance is characterized as the
following:
•
The Bulk Electric System (BES) shall demonstrate transient, dynamic and
voltage stability.
•
All Facilities shall be within their continuous Facility Ratings and thermal limits
•
All Facilities shall be within their pre-contingency voltage limits
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•
All Facilities shall be within stability limits.
As per the Peak Reliability SOL Methodology (based on NERC Standard, FAC-011,
R2.2), acceptable post-contingency performance is characterized as the following:
•
The BES shall demonstrate transient, dynamic and voltage stability
•
All Facilities shall be within their applicable short-term Facility Ratings and
thermal limits
•
All Facilities shall be within their post-contingency voltage limits
•
All Facilities shall be within stability limits
•
Cascading or uncontrolled separation shall not occur
The Peak Reliability SOL Methodology for the Operations Horizon states if any of the
acceptable pre- or post-contingency system performance criteria stipulated in this
Methodology are not being met, an SOL is being exceeded. Conditions that expose the
system to unacceptable BES performance cannot be allowed to continue indefinitely. As
such, when the system is experiencing unacceptable pre- or post-contingency
performance, the system must be adjusted as soon as practicable, to prepare for the
next contingency.
When system studies conducted throughout the Operations Horizon (including Realtime Assessments) indicate that any of the acceptable post-contingency system
performance criteria are not being met, the Transmission Operator (TOP) shall take precontingency actions to achieve acceptable performance. These actions may include 1,
but are not limited to, the following:
•
Commit and redispatch generation
•
Make adjustments to the uses of the transmission system (e.g., schedule
curtailments/adjustments)
•
Make changes to system topology
Mitigation Plan Viability
A Pre- or Post-Contingency Mitigation Plan is viable when:
•
The TOP understands exactly what the limiting conditions/elements are.
•
The TOP knows specifically what the mitigation plan is, knows that the plan will
actually resolve the reliability issue, and has communicated the specifics of the
plan to impacted TOP’s and to the RC System Operator.
•
The mitigation plan does not adversely impact neighboring TOP and Balancing
Authority Areas.
1
Notwithstanding anything in this guideline, TOPs maintain the authority to take action up to and
including shedding firm load to ensure the reliability of the BES
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•
If the mitigation plan involves actions by neighboring TOPs and Balancing
Authorities they have indicated their support of the mitigation plan through some
form of bilateral coordination.
•
•
The RC System Operator (RCSO) has evaluated the mitigation plan and
determined that the plan resolves the reliability issue in a timely manner.
•
The TOP provides the RCSO adequate information on the time needed to
complete mitigating actions that indicates that the plan can be implemented in
sufficient time.
Even with operations planning processes and real-time tools and assessments, it is
possible that a TOP may find themselves unexpectedly in an N-1 insecure state. TOPs
should review existing operating processes and procedures to ensure that postcontingency mitigation plans reflect the time necessary to take mitigating actions,
including control actions, to return the system to a secure N-1 state as soon as possible
but no longer than 30 minutes following a single contingency. As part of this review,
TOPs should consider the effect of relays that automatically isolate facilities without
providing operators sufficient time to take mitigating measures.
Automatic Mitigating Actions
Automatic actions such as Remedial Action Schemes (RAS) or Special Protection
Systems (SPS) are appropriate for mitigating post-contingency exceedances of Facility
Ratings, bus voltage limits, or stability limits. The RAS or SPS must be available and
armed for it to be considered a viable automatic mitigation plan.
RTCA indication of any post-Contingency conditions demonstrating
unacceptable N-1 system performance
Western Interconnection entities should refer to the Peak Reliability Monitoring of RealTime SOL and IROL Exceedances Procedure, Section C that describes the appropriate
actions for operating conditions where Real-Time Contingency Analysis (RTCA)
indicates post-contingency exceedance of the highest available Facility Rating, voltage
limit, or stability limit. The procedure describes when TOPs are required to take precontingency action to prevent unacceptable post-contingency system performance.
Other Considerations
This guideline describes general expectations for mitigating pre- and post-contingency
exceedances in the Western Interconnection. There may be situations where due to
planned or forced outages, for example, the system is unable to demonstrate
acceptable post-contingency system performance without shedding load precontingency. In these situations, the TOP is expected to ensure that instability,
cascading, or uncontrolled separation shall not occur. This is demonstrated through
prior studies and using reasonable judgment in assessing the risks associated with
post-contingency exceedances. Pre- or post-contingency mitigation should take place
Page 4 of 5
through appropriate means depending on the risks and the options available to the
TOP. TOPs judgment and other considerations such as safety, equipment damage, or
regulatory or statutory requirements must always be considered.
It should be recognized that this is a Guideline and can be superseded by a Directive
from the Reliability Coordinator.
Approved By:
Approving Committee, Entity or Person
Date
Operating Committee
May 20, 2014
Operating Issues Work Group
February 21, 2014
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